diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4a8ce44d4..506d3d2ac 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -25,8 +25,10 @@ jobs:
     steps:
     - name: Set up environment
       uses: actions/checkout@v1
-      with:  # no need for the history
-        fetch-depth: 1
+      with:
+        # Fetch all commits so that versioneer will return something compatible
+        # with semantic-version
+        fetch-depth: 0
     - name: Set up Python ${{ matrix.python }}
       uses: actions/setup-python@v1
       with:
diff --git a/dandi/cli/cmd_download.py b/dandi/cli/cmd_download.py
index 2e4d7ebc8..373461542 100644
--- a/dandi/cli/cmd_download.py
+++ b/dandi/cli/cmd_download.py
@@ -55,7 +55,7 @@
 )
 @click.argument("url", nargs=-1)
 @map_to_click_exceptions
-def download(url, output_dir, existing, jobs=6, format="pytout"):
+def download(url, output_dir, existing, jobs, format):
     """Download a file or entire folder from DANDI"""
     # First boring attempt at click commands being merely an interface to
     # Python function
diff --git a/dandi/cli/formatter.py b/dandi/cli/formatter.py
index 6dc28253a..dd851531b 100644
--- a/dandi/cli/formatter.py
+++ b/dandi/cli/formatter.py
@@ -45,9 +45,10 @@ def __init__(self, out=None):
         self.records = []
 
     def __exit__(self, exc_type, exc_value, traceback):
-        import yaml
+        import ruamel.yaml
 
-        self.out.write(yaml.dump(self.records))
+        yaml = ruamel.yaml.YAML()
+        yaml.dump(self.records, self.out)
 
     def __call__(self, rec):
         self.records.append(rec)
diff --git a/dandi/cli/tests/test_ls.py b/dandi/cli/tests/test_ls.py
index 19f29fd4b..d04f52f61 100644
--- a/dandi/cli/tests/test_ls.py
+++ b/dandi/cli/tests/test_ls.py
@@ -2,6 +2,7 @@
 import pytest
 
 from ..command import ls
+from ...utils import yaml_load
 
 
 @pytest.mark.parametrize("format", ("auto", "json", "json_pp", "yaml", "pyout"))
@@ -17,10 +18,9 @@ def test_smoke(simple1_nwb_metadata, simple1_nwb, format):
 
         load = json.loads
     elif format == "yaml":
-        import yaml
 
         def load(s):
-            obj = yaml.load(s, Loader=yaml.BaseLoader)
+            obj = yaml_load(s, typ="base")
             assert len(obj) == 1  # will be a list with a single elem
             return obj[0]
 
diff --git a/dandi/conftest.py b/dandi/conftest.py
index 8a791c1e7..e07338088 100644
--- a/dandi/conftest.py
+++ b/dandi/conftest.py
@@ -1 +1 @@
-from .tests.fixtures import *
+from .tests.fixtures import *  # noqa: F401, F403
diff --git a/dandi/consts.py b/dandi/consts.py
index 2e1da5f96..eab3d3fbe 100644
--- a/dandi/consts.py
+++ b/dandi/consts.py
@@ -75,9 +75,7 @@
 dandiset_metadata_file = "dandiset.yaml"
 dandiset_identifier_regex = "^[0-9]{6}$"
 
-dandi_instance = namedtuple(
-    "dandi_instance", ("girder", "gui", "redirector", "dandiapi")
-)
+dandi_instance = namedtuple("dandi_instance", ("girder", "gui", "redirector", "api"))
 
 known_instances = {
     "local-girder-only": dandi_instance(
@@ -118,7 +116,7 @@
 # Chunk size when iterating a download (and upload) body. Taken from girder-cli
 # TODO: should we make them smaller for download than for upload?
 # ATM used only in download
-MAX_CHUNK_SIZE = os.environ.get("DANDI_MAX_CHUNK_SIZE", 1024 * 1024 * 8)  # 64
+MAX_CHUNK_SIZE = int(os.environ.get("DANDI_MAX_CHUNK_SIZE", 1024 * 1024 * 8))  # 64
 
 #
 # Some routes
diff --git a/dandi/dandiapi.py b/dandi/dandiapi.py
index e123c1aad..930c56794 100644
--- a/dandi/dandiapi.py
+++ b/dandi/dandiapi.py
@@ -9,16 +9,6 @@
 lgr = get_logger()
 
 
-class HTTPError(requests.HTTPError):
-    """An HTTP error occurred.
-
-    Following Girder's recommendation of having its HttpError deprecated,
-    this is just a helper to bring that HTTPError into our space
-    """
-
-    pass
-
-
 # Following class is loosely based on GirderClient, with authentication etc
 # being stripped.
 # TODO: add copyright/license info
@@ -56,10 +46,13 @@ def session(self, session=None):
         """
         self._session = session if session else requests.Session()
 
-        yield self._session
-
-        self._session.close()
-        self._session = None
+        try:
+            yield self._session
+        finally:
+            # close only if we started a new one
+            if not session:
+                self._session.close()
+            self._session = None
 
     def _request_func(self, method):
         if self._session is not None:
@@ -141,8 +134,8 @@ def send_request(
         )
 
         # If success, return the json object. Otherwise throw an exception.
-        if result.status_code not in (200, 201):
-            raise HTTPError(
+        if not result.ok:
+            raise requests.HTTPError(
                 f"Error {result.status_code} while sending {method} request to {url}",
                 response=result,
             )
@@ -234,9 +227,7 @@ def get_asset(self, dandiset_id, version, uuid):
     def get_dandiset(self, dandiset_id, version):
         return self.get(f"/dandisets/{dandiset_id}/versions/{version}/")
 
-    def get_dandiset_assets(
-        self, dandiset_id, version, location=None, page_size=None, include_metadata=True
-    ):
+    def get_dandiset_assets(self, dandiset_id, version, location=None, page_size=None):
         """A generator to provide asset records
         """
         if location is not None:
@@ -297,13 +288,11 @@ def get_dandiset_assets(
                     r["modified"] = ensure_datetime(uploaded_mtime)
             yield r
 
-    def get_dandiset_and_assets(
-        self, dandiset_id, version, location=None, include_metadata=True
-    ):
+    def get_dandiset_and_assets(self, dandiset_id, version, location=None):
         """This is pretty much an adapter to provide "harmonized" output in both
-        girder and dandiapi clients.
+        girder and DANDI api clients.
 
-        Harmonization should happen toward "dandiapi" BUT AFAIK it is still influx
+        Harmonization should happen toward DADNDI API BUT AFAIK it is still influx
         """
         # Fun begins!
         location_ = "/" + location if location else ""
@@ -320,9 +309,7 @@ def get_dandiset_and_assets(
         # Get dandiset information
         dandiset = self.get_dandiset(dandiset_id, version)
         # TODO: location
-        assets = self.get_dandiset_assets(
-            dandiset_id, version, location=location, include_metadata=include_metadata
-        )
+        assets = self.get_dandiset_assets(dandiset_id, version, location=location)
         return dandiset, assets
 
     def get_download_file_iter(
diff --git a/dandi/dandiset.py b/dandi/dandiset.py
index b00379722..c9b0c11cd 100644
--- a/dandi/dandiset.py
+++ b/dandi/dandiset.py
@@ -1,11 +1,10 @@
 """Classes/utilities for support of a dandiset"""
 
 import os
-import yaml
 from pathlib import Path
 
 from .consts import dandiset_metadata_file
-from .utils import find_parent_directory_containing, yaml_dump
+from .utils import find_parent_directory_containing, yaml_dump, yaml_load
 
 from . import get_logger
 
@@ -42,7 +41,7 @@ def _load_metadata(self):
             with open(self._metadata_file_obj) as f:
                 # TODO it would cast 000001 if not explicitly string into
                 # an int -- we should prevent it... probably with some custom loader
-                self.metadata = yaml.safe_load(f)
+                self.metadata = yaml_load(f, typ="safe")
         else:
             self.metadata = None
 
@@ -70,15 +69,9 @@ def update_metadata(self, meta):
             lgr.debug("No updates to metadata, returning")
             return
 
-        # We will use ruaml to load/save it
-        # Seems to be too tricky to add new entries, etc so we will
-        # just resort to explicitly adding the header while saving
-        # import ruamel.yaml
-        # yaml = ruamel.yaml.YAML()  # defaults to round-trip if no parameters
-        # given
         if self._metadata_file_obj.exists():
             with open(self._metadata_file_obj) as f:
-                rec = yaml.safe_load(f)
+                rec = yaml_load(f, typ="safe")
         else:
             rec = {}
 
diff --git a/dandi/download.py b/dandi/download.py
index 8dca651c5..6c39d7b2a 100644
--- a/dandi/download.py
+++ b/dandi/download.py
@@ -20,7 +20,7 @@
 )
 from .dandiset import Dandiset
 from .exceptions import FailedToConnectError, NotFoundError, UnknownURLError
-from .utils import flattened, is_same_time
+from .utils import flattened, is_same_time, get_instance
 
 import humanize
 from .support.pyout import naturalsize
@@ -44,7 +44,7 @@ class _dandi_url_parser:
         #   - 'only' - would interrupt if no redirection happens
         # server_type:
         #   - 'girder' - the default/old
-        #   - 'dandiapi' - the "new" (as of 20200715 state of various PRs)
+        #   - 'api' - the "new" (as of 20200715 state of various PRs)
         # rewrite:
         #   - callable -- which would rewrite that "URI"
         "DANDI:": {"rewrite": lambda x: "https://identifiers.org/" + x},
@@ -69,7 +69,7 @@ class _dandi_url_parser:
         "/(?P<version>([.0-9]{5,}|draft))"
         "(/files(\\?location=(?P<location>.*)?)?)?"
         f"(/files(\\?_id={id_grp}(&_modelType=folder)?)?)?"
-        "$": {"server_type": "dandiapi"},
+        "$": {"server_type": "api"},
         # https://deploy-preview-341--gui-dandiarchive-org.netlify.app/#/dandiset/000006/draft
         # (no API yet)
         "https?://.*": {"handle_redirect": "only"},
@@ -77,12 +77,12 @@ class _dandi_url_parser:
     # We might need to remap some assert_types
     map_asset_types = {"dandiset": "folder"}
     # And lets create our mapping into girder instances from known_instances:
-    map_to = {"girder": {}, "dandiapi": {}}
-    for girder, gui, redirector, dandiapi in known_instances.values():  # noqa: F402
+    map_to = {"girder": {}, "api": {}}
+    for girder, gui, redirector, api in known_instances.values():  # noqa: F402
         for h in (gui, redirector):
             if h:
                 map_to["girder"][h] = girder
-                map_to["dandiapi"][h] = dandiapi
+                map_to["api"][h] = api
 
     @classmethod
     def parse(cls, url, *, map_instance=True):
@@ -165,7 +165,7 @@ def parse(cls, url, *, map_instance=True):
                                 settings["map_instance"], ", ".join(known_instances)
                             )
                         )
-                    known_instance = known_instances[settings["map_instance"]]
+                    known_instance = get_instance(settings["map_instance"])
                     # for consistency, add
                     server = getattr(known_instance, server_type)
                     if not server.endswith("/"):
@@ -205,7 +205,7 @@ def parse(cls, url, *, map_instance=True):
                     i.split("+")[1] for i in groups["multiitem"].split("/") if i
                 ]
                 asset_type = "item"
-        elif server_type == "dandiapi":
+        elif server_type == "api":
             asset_type = groups.get("asset_type")
             dandiset_id = groups.get("dandiset_id")
             version = groups.get("version")
@@ -270,123 +270,33 @@ def download(urls, output_dir, *, format="pyout", existing="error", jobs=1):
     import pyout
     from .support import pyout as pyouts
 
-    class ItemsSummary:
-        def __init__(self):
-            self.files = 0
-            self.t0 = None  # when first record is seen
-            self.size = 0
-            self.has_unknown_sizes = False
-
-        def __call__(self, rec, prior=None):
-            assert prior in (None, self)
-            if not self.files:
-                self.t0 = time.time()
-            self.files += 1
-            size = rec.get("size")
-            if size is not None:
-                self.size += size
-            elif rec.get("path", "") == "dandiset.yaml":
-                # again -- so special. TODO: make it a proper file
-                pass
-            else:
-                self.has_unknown_sizes = True
-            return self
-
     # dandi.cli.formatters are used in cmd_ls to provide switchable
     pyout_style = pyouts.get_style(hide_if_missing=False)
 
     rec_fields = ("path", "size", "done", "done%", "checksum", "status", "message")
     out = pyout.Tabular(style=pyout_style, columns=rec_fields, max_workers=jobs)
 
-    # Establish "fancy" download while still possibly traversing the dandiset
-    # functionality.
-    from .support.iterators import IteratorWithAggregation
-
-    items_summary = ItemsSummary()
-    it = IteratorWithAggregation(
-        # unfortunately Yarik missed the point that we need to wrap
-        # "assets" generator within downloader_generator
-        # so we do not have assets here!  Ad-hoc solution for now is to
-        # pass this beast so it could get .gen set within downloader_generator
-        None,  # download_generator(urls, output_dir, existing=existing),
-        items_summary,
-    )
-
-    def agg_files(*ignored):
-        ret = str(items_summary.files)
-        if not it.finished:
-            ret += "+"
-        return ret
-
-    def agg_size(sizes):
-        """Formatter for "size" column where it would show
-
-        how much is "active" (or done)
-        +how much yet to be "shown".
-        """
-        active = sum(sizes)
-        if (active, items_summary.size) == (0, 0):
-            return ""
-        v = [naturalsize(active)]
-        if not it.finished or (
-            active != items_summary.size or items_summary.has_unknown_sizes
-        ):
-            extra = items_summary.size - active
-            if extra < 0:
-                lgr.debug("Extra size %d < 0 -- must not happen", extra)
-            else:
-                extra_str = "+%s" % naturalsize(extra)
-                if not it.finished:
-                    extra_str = ">" + extra_str
-                if items_summary.has_unknown_sizes:
-                    extra_str += "+?"
-                v.append(extra_str)
-        return v
-
-    def agg_done(done_sizes):
-        """Formatter for "DONE" column
-        """
-        done = sum(done_sizes)
-        if it.finished and done == 0 and items_summary.size == 0:
-            # even with 0s everywhere consider it 100%
-            r = 1.0
-        elif items_summary.size:
-            r = done / items_summary.size
-        else:
-            r = 0
-        pref = ""
-        if not it.finished:
-            pref += "<"
-        if items_summary.has_unknown_sizes:
-            pref += "?"
-        v = [naturalsize(done), "%s%.2f%%" % (pref, 100 * r)]
-        if done and items_summary.t0 is not None and r and items_summary.size != 0:
-            dt = time.time() - items_summary.t0
-            more_time = dt / r if r != 1 else 0
-            more_time_str = humanize.naturaldelta(more_time)
-            if not it.finished:
-                more_time_str += "<"
-            if items_summary.has_unknown_sizes:
-                more_time_str += "+?"
-            if more_time:
-                v.append("ETA: %s" % more_time_str)
-        return v
-
+    out_helper = PYOUTHelper()
     pyout_style["done"] = pyout_style["size"].copy()
-    pyout_style["size"]["aggregate"] = agg_size
-    pyout_style["done"]["aggregate"] = agg_done
+    pyout_style["size"]["aggregate"] = out_helper.agg_size
+    pyout_style["done"]["aggregate"] = out_helper.agg_done
 
     # I thought I was making a beautiful flower but ended up with cacti
     # which never blooms... All because assets are looped through inside download_generator
     # TODO: redo
-    kw = dict(assets_it=it)
+    kw = dict(assets_it=out_helper.it)
     if jobs > 1 and format == "pyout":
         # It could handle delegated to generator downloads
         kw["yield_generator_for_fields"] = rec_fields[1:]  # all but path
 
     gen_ = download_generator(urls, output_dir, existing=existing, **kw)
 
-    # TODO: redo frontends similarly to how command_ls did it
+    # TODOs:
+    #  - redo frontends similarly to how command_ls did it
+    #  - have a single loop with analysis of `rec` to either any file
+    #    has failed to download.  If any was: exception should probably be
+    #    raised.  API discussion for Python side of API:
+    #
     if format == "debug":
         for rec in gen_:
             print(rec)
@@ -436,7 +346,7 @@ def download_generator(
     # We could later try to "dandi_authenticate" if run into permission issues.
     # May be it could be not just boolean but the "id" to be used?
     # TODO: remove whenever API starts to support drafts in an unknown version
-    if server_type == "dandiapi" and asset_id.get("version") == "draft":
+    if server_type == "api" and asset_id.get("version") == "draft":
         asset_id, asset_type, client, server_type = _map_to_girder(url)
         args = asset_id, asset_type
     elif server_type == "girder":
@@ -444,7 +354,7 @@ def download_generator(
             server_url, authenticate=False, progressbars=True  # TODO: redo all this
         )
         args = asset_id, asset_type
-    elif server_type == "dandiapi":
+    elif server_type == "api":
         client = DandiAPIClient(server_url)
         args = (asset_id["dandiset_id"], asset_id["version"], asset_id.get("location"))
     else:
@@ -491,7 +401,7 @@ def download_generator(
             if server_type == "girder":
                 down_args = (asset["id"],)
                 digests = digests_from_metadata
-            elif server_type == "dandiapi":
+            elif server_type == "api":
                 # Even worse to get them from the asset record which also might have its return
                 # record still changed, https://github.com/dandi/dandi-publish/issues/79
                 down_args = args[:2] + (asset["uuid"],)
@@ -541,9 +451,129 @@ def download_generator(
                     yield dict(resp, path=path)
 
 
+class ItemsSummary:
+    """A helper "structure" to accumulate information about assets to be downloaded
+
+    To be used as a callback to IteratorWithAggregation
+    """
+
+    def __init__(self):
+        self.files = 0
+        # TODO: get rid of needing it
+        self.t0 = None  # when first record is seen
+        self.size = 0
+        self.has_unknown_sizes = False
+
+    def as_dict(self):
+        return {a: getattr(self, a) for a in ("files", "size", "has_unknown_sizes")}
+
+    def __call__(self, rec, prior=None):
+        assert prior in (None, self)
+        if not self.files:
+            self.t0 = time.time()
+        self.files += 1
+        size = rec.get("size")
+        if size is not None:
+            self.size += size
+        elif rec.get("path", "") == "dandiset.yaml":
+            # again -- so special. TODO: make it a proper file
+            pass
+        else:
+            self.has_unknown_sizes = True
+        return self
+
+
+class PYOUTHelper:
+    """Helper for PYOUT styling
+
+    Provides aggregation callbacks for PyOUT and also an iterator to be wrapped around
+    iterating over assets, so it would get "totals" as soon as they are available.
+    """
+
+    def __init__(self):
+        # Establish "fancy" download while still possibly traversing the dandiset
+        # functionality.
+        from .support.iterators import IteratorWithAggregation
+
+        self.items_summary = ItemsSummary()
+        self.it = IteratorWithAggregation(
+            # unfortunately Yarik missed the point that we need to wrap
+            # "assets" generator within downloader_generator
+            # so we do not have assets here!  Ad-hoc solution for now is to
+            # pass this beast so it could get .gen set within downloader_generator
+            None,  # download_generator(urls, output_dir, existing=existing),
+            self.items_summary,
+        )
+
+    def agg_files(self, *ignored):
+        ret = str(self.items_summary.files)
+        if not self.it.finished:
+            ret += "+"
+        return ret
+
+    def agg_size(self, sizes):
+        """Formatter for "size" column where it would show
+
+        how much is "active" (or done)
+        +how much yet to be "shown".
+        """
+        active = sum(sizes)
+        if (active, self.items_summary.size) == (0, 0):
+            return ""
+        v = [naturalsize(active)]
+        if not self.it.finished or (
+            active != self.items_summary.size or self.items_summary.has_unknown_sizes
+        ):
+            extra = self.items_summary.size - active
+            if extra < 0:
+                lgr.debug("Extra size %d < 0 -- must not happen", extra)
+            else:
+                extra_str = "+%s" % naturalsize(extra)
+                if not self.it.finished:
+                    extra_str = ">" + extra_str
+                if self.items_summary.has_unknown_sizes:
+                    extra_str += "+?"
+                v.append(extra_str)
+        return v
+
+    def agg_done(self, done_sizes):
+        """Formatter for "DONE" column
+        """
+        done = sum(done_sizes)
+        if self.it.finished and done == 0 and self.items_summary.size == 0:
+            # even with 0s everywhere consider it 100%
+            r = 1.0
+        elif self.items_summary.size:
+            r = done / self.items_summary.size
+        else:
+            r = 0
+        pref = ""
+        if not self.it.finished:
+            pref += "<"
+        if self.items_summary.has_unknown_sizes:
+            pref += "?"
+        v = [naturalsize(done), "%s%.2f%%" % (pref, 100 * r)]
+        if (
+            done
+            and self.items_summary.t0 is not None
+            and r
+            and self.items_summary.size != 0
+        ):
+            dt = time.time() - self.items_summary.t0
+            more_time = dt / r if r != 1 else 0
+            more_time_str = humanize.naturaldelta(more_time)
+            if not self.it.finished:
+                more_time_str += "<"
+            if self.items_summary.has_unknown_sizes:
+                more_time_str += "+?"
+            if more_time:
+                v.append("ETA: %s" % more_time_str)
+        return v
+
+
 def _map_to_girder(url):
     """
-    "draft" datasets are not yet supported through dandiapi. So we need to
+    "draft" datasets are not yet supported through our DANDI API. So we need to
     perform special handling for now: discover girder_id for it and then proceed
     with girder
     """
@@ -576,7 +606,7 @@ def _map_to_girder(url):
     return asset_id, asset_type, client, server_type
 
 
-def skip_file(msg):
+def _skip_file(msg):
     return {"status": "skipped", "message": str(msg)}
 
 
@@ -590,7 +620,7 @@ def _populate_dandiset_yaml(dandiset_path, metadata, overwrite):
     yield {"message": "updating"}
     lgr.debug(f"Updating {dandiset_metadata_file} from obtained dandiset " f"metadata")
     if op.lexists(dandiset_yaml) and not overwrite:
-        yield skip_file("already exists")
+        yield _skip_file("already exists")
         return
     else:
         dandiset = Dandiset(dandiset_path, allow_empty=True)
@@ -618,7 +648,7 @@ def _download_file(
     Parameters
     ----------
     downloader: callable returning a generator
-      A backend (girder or dandiapi) specific fixture for downloading some file into
+      A backend (girder or api) specific fixture for downloading some file into
       path. It should be a generator yielding downloaded blocks.
     size: int, optional
       Target size if known
@@ -631,7 +661,7 @@ def _download_file(
         if existing == "error":
             raise FileExistsError(block)
         elif existing == "skip":
-            yield skip_file("already exists")
+            yield _skip_file("already exists")
             return
         elif existing == "overwrite":
             pass
@@ -651,7 +681,7 @@ def _download_file(
                 # but mtime is different
                 if same == ["mtime", "size"]:
                     # TODO: add recording and handling of .nwb object_id
-                    yield skip_file("same time and size")
+                    yield _skip_file("same time and size")
                     return
                 lgr.debug(f"{path!r} - same attributes: {same}.  Redownloading")
 
@@ -692,6 +722,7 @@ def _download_file(
                     msg = {"done": downloaded}
                     if size:
                         if downloaded > size and not warned:
+                            warned = True
                             # Yield ERROR?
                             lgr.warning(
                                 "Downloaded %d bytes although size was told to be just %d",
diff --git a/dandi/exceptions.py b/dandi/exceptions.py
index ce64b587d..c004be2a0 100644
--- a/dandi/exceptions.py
+++ b/dandi/exceptions.py
@@ -23,3 +23,40 @@ class FailedToConnectError(RuntimeError):
     """Failed to connect to online resource"""
 
     pass
+
+
+class LockingError(RuntimeError):
+    """Failed to lock or unlock a resource"""
+
+    pass
+
+
+class CliVersionError(RuntimeError):
+    """ Base class for `CliVersionTooOldError` and `BadCliVersionError` """
+
+    def __init__(self, our_version, minversion, bad_versions):
+        self.our_version = our_version
+        self.minversion = minversion
+        self.bad_versions = bad_versions
+
+    def server_requirements(self):
+        s = f"Server requires at least version {self.minversion}"
+        if self.bad_versions:
+            s += f" (but not {', '.join(map(str, self.bad_versions))})"
+        return s
+
+
+class CliVersionTooOldError(CliVersionError):
+    def __str__(self):
+        return (
+            f"Client version {self.our_version} is too old!  "
+            + self.server_requirements()
+        )
+
+
+class BadCliVersionError(CliVersionError):
+    def __str__(self):
+        return (
+            f"Client version {self.our_version} is rejected by server!  "
+            + self.server_requirements()
+        )
diff --git a/dandi/girder.py b/dandi/girder.py
index 594210985..2aefdf66b 100644
--- a/dandi/girder.py
+++ b/dandi/girder.py
@@ -1,7 +1,8 @@
-import os
-import os.path as op
+import contextlib
 import json
 import keyring
+import os
+import os.path as op
 import random
 import sys
 import time
@@ -12,8 +13,9 @@
 import girder_client as gcl
 
 from . import get_logger
-from .consts import MAX_CHUNK_SIZE, known_instances_rev
+from .exceptions import LockingError
 from .utils import ensure_datetime, flattened, flatten, remap_dict
+from .consts import known_instances_rev, MAX_CHUNK_SIZE
 
 lgr = get_logger()
 
@@ -30,6 +32,8 @@ class GirderNotFound(Exception):
     pass
 
 
+# TODO: remove if we start to expose this as a Python library which could
+# be longer lived than just a CLI
 @lru_cache(1024)
 def lookup(client, name, asset_type="collection", path=None):
     """A helper for common logic while looking up things on girder by name"""
@@ -488,6 +492,29 @@ def get_dandiset_and_assets(
             ),
         )
 
+    @contextlib.contextmanager
+    def lock_dandiset(self, dandiset_identifier: str):
+        presumably_locked = False
+        try:
+            lgr.debug("Trying to acquire lock for %s", dandiset_identifier)
+            try:
+                self.post(f"dandi/{dandiset_identifier}/lock")
+            except gcl.HttpError:
+                raise LockingError(f"Failed to lock dandiset {dandiset_identifier}")
+            else:
+                presumably_locked = True
+
+            yield
+        finally:
+            if presumably_locked:
+                lgr.debug("Trying to release the lock for %s", dandiset_identifier)
+                try:
+                    self.post(f"dandi/{dandiset_identifier}/unlock")
+                except gcl.HttpError:
+                    raise LockingError(
+                        f"Failed to unlock dandiset {dandiset_identifier}"
+                    )
+
 
 def _harmonize_girder_dandiset_to_dandi_api(rec):
     """
diff --git a/dandi/organize.py b/dandi/organize.py
index 987ebc69e..e88896e80 100644
--- a/dandi/organize.py
+++ b/dandi/organize.py
@@ -13,7 +13,7 @@
 from .exceptions import OrganizeImpossibleError
 from . import get_logger
 from .pynwb_utils import get_neurodata_types_to_modalities_map, get_object_id
-from .utils import ensure_datetime, flattened
+from .utils import ensure_datetime, flattened, yaml_load
 
 lgr = get_logger()
 
@@ -467,7 +467,7 @@ def populate_dataset_yml(filepath, metadata):
             pass
 
     with open(filepath) as f:
-        rec = yaml.load(f)
+        rec = yaml_load(f)
 
     if not rec:
         rec = {}
diff --git a/dandi/register.py b/dandi/register.py
index 870304898..6b4c3d9b6 100644
--- a/dandi/register.py
+++ b/dandi/register.py
@@ -3,14 +3,15 @@
 
 from . import get_logger
 from . import girder
-from .consts import dandiset_metadata_file, known_instances, routes
+from .consts import dandiset_metadata_file, routes
 from .dandiset import Dandiset
+from .utils import get_instance
 
 lgr = get_logger()
 
 
 def register(name, description, dandiset_path=None, dandi_instance="dandi"):
-    dandi_instance = known_instances[dandi_instance]
+    dandi_instance = get_instance(dandi_instance)
     if not dandiset_path and op.exists(dandiset_metadata_file):
         dandiset = Dandiset.find(os.getcwd())
         if dandiset:
diff --git a/dandi/support/iterators.py b/dandi/support/iterators.py
index ed608f614..f08c756b2 100644
--- a/dandi/support/iterators.py
+++ b/dandi/support/iterators.py
@@ -100,6 +100,9 @@ def worker():
 
         # yield from the queue (.total and .finished could be accessed meanwhile)
         while True:
+            if self.reraise_immediately and self._exc is not None:
+                break
+
             # race condition HERE between checking for self.finished and
             if self.finished and queue.empty():
                 break
@@ -109,8 +112,6 @@ def worker():
                 yield queue.get(timeout=0.001)
             except Empty:
                 continue
-            if self.reraise_immediately and self._exc is not None:
-                break
         t.join()
         if self._exc is not None:
             raise self._exc
diff --git a/dandi/support/tests/test_cache.py b/dandi/support/tests/test_cache.py
index 5bb5c40d3..139a8c6cb 100644
--- a/dandi/support/tests/test_cache.py
+++ b/dandi/support/tests/test_cache.py
@@ -185,9 +185,9 @@ def func(path):
         # must be running during conda build which blows up paths with
         # _placehold_ers
         pytest.skip("seems to be running on conda and hitting the limits")
-    assert outputs[0].stdout.strip().decode() == f"Running script.py.DONE"
+    assert outputs[0].stdout.strip().decode() == "Running script.py.DONE"
     for o in outputs[1:]:
-        assert o.stdout.strip().decode() == f"DONE"
+        assert o.stdout.strip().decode() == "DONE"
 
     cache.clear()
 
diff --git a/dandi/support/tests/test_digests.py b/dandi/support/tests/test_digests.py
index 0792fa8f4..fa410e983 100644
--- a/dandi/support/tests/test_digests.py
+++ b/dandi/support/tests/test_digests.py
@@ -19,7 +19,9 @@ def test_digester(tmp_path):
         "md5": "202cb962ac59075b964b07152d234b70",
         "sha1": "40bd001563085fc35165329ea1ff5c5ecbdbbeef",
         "sha256": "a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3",
-        "sha512": "3c9909afec25354d551dae21590bb26e38d53f2173b8d3dc3eee4c047e7ab1c1eb8b85103e3be7ba613b31bb5c9c36214dc9f14a42fd7a2fdb84856bca5c44c2",
+        "sha512": "3c9909afec25354d551dae21590bb26e38d53f2173b8d3dc3eee4c047e7a"
+                  "b1c1eb8b85103e3be7ba613b31bb5c9c36214dc9f14a42fd7a2fdb84856b"
+                  "ca5c44c2",
     }
 
     f = tmp_path / "0"
@@ -28,7 +30,9 @@ def test_digester(tmp_path):
         "md5": "93b885adfe0da089cdf634904fd59f71",
         "sha1": "5ba93c9db0cff93f52b521d7420e43f6eda2784f",
         "sha256": "6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d",
-        "sha512": "b8244d028981d693af7b456af8efa4cad63d282e19ff14942c246e50d9351d22704a802a71c3580b6370de4ceb293c324a8423342557d4e5c38438f0e36910ee",
+        "sha512": "b8244d028981d693af7b456af8efa4cad63d282e19ff14942c246e50d935"
+                  "1d22704a802a71c3580b6370de4ceb293c324a8423342557d4e5c38438f0"
+                  "e36910ee",
     }
 
     f = tmp_path / "long.txt"
@@ -37,5 +41,7 @@ def test_digester(tmp_path):
         "md5": "81b196e3d8a1db4dd2e89faa39614396",
         "sha1": "5273ac6247322c3c7b4735a6d19fd4a5366e812f",
         "sha256": "80028815b3557e30d7cbef1d8dbc30af0ec0858eff34b960d2839fd88ad08871",
-        "sha512": "684d23393eee455f44c13ab00d062980937a5d040259d69c6b291c983bf635e1d405ff1dc2763e433d69b8f299b3f4da500663b813ce176a43e29ffcc31b0159",
+        "sha512": "684d23393eee455f44c13ab00d062980937a5d040259d69c6b291c983bf6"
+                  "35e1d405ff1dc2763e433d69b8f299b3f4da500663b813ce176a43e29ffc"
+                  "c31b0159",
     }
diff --git a/dandi/support/tests/test_iterators.py b/dandi/support/tests/test_iterators.py
index 4d9d37f99..15549b0e4 100644
--- a/dandi/support/tests/test_iterators.py
+++ b/dandi/support/tests/test_iterators.py
@@ -15,7 +15,8 @@ def sleeping_range(n, secs=0.01, thr=None):
 
 
 def test_IteratorWithAggregation():
-    sumup = lambda v, t=0: v + t
+    def sumup(v, t=0):
+        return v + t
 
     it = IteratorWithAggregation(sleeping_range(3, 0.0001), agg=sumup)
     # we should get our summary available after 2nd iteration and before it finishes
diff --git a/dandi/tests/data/dandiarchive-docker/docker-compose.yml b/dandi/tests/data/dandiarchive-docker/docker-compose.yml
index ef0a109c3..5b825e21f 100644
--- a/dandi/tests/data/dandiarchive-docker/docker-compose.yml
+++ b/dandi/tests/data/dandiarchive-docker/docker-compose.yml
@@ -42,7 +42,7 @@ services:
     ports:
       - "8079:8080"
     environment:
-      GIRDER_URL: http://girder:8080
+      GIRDER_URL: http://localhost:8081
       GUI_URL: http://localhost:8086
       ABOUT_URL: http://www.dandiarchive.org
 
diff --git a/dandi/tests/fixtures.py b/dandi/tests/fixtures.py
index 6b9f4640d..ef46e83a9 100644
--- a/dandi/tests/fixtures.py
+++ b/dandi/tests/fixtures.py
@@ -18,6 +18,7 @@
 
 lgr = get_logger()
 
+
 # TODO: move into some common fixtures.  We might produce a number of files
 #       and also carry some small ones directly in git for regression testing
 @pytest.fixture(scope="session")
diff --git a/dandi/tests/skip.py b/dandi/tests/skip.py
index 9cfd959ec..93f10b8e5 100644
--- a/dandi/tests/skip.py
+++ b/dandi/tests/skip.py
@@ -96,7 +96,7 @@ def windows():
 #     return msg, missing_deps
 
 # The following code is modified from the original ReproMan source:
-### BEGIN MODIFIED CODE
+# ### BEGIN MODIFIED CODE
 
 
 def no_docker_commands():
@@ -121,7 +121,7 @@ def is_engine_running():
     return "docker engine not running", not is_engine_running()
 
 
-### END MODIFIED CODE
+# ### END MODIFIED CODE
 
 
 def no_network():
diff --git a/dandi/tests/test_download.py b/dandi/tests/test_download.py
index e31c6d95a..5ae5732d5 100644
--- a/dandi/tests/test_download.py
+++ b/dandi/tests/test_download.py
@@ -20,10 +20,10 @@ def _assert_parse_girder_url(url):
     return a, aid
 
 
-def _assert_parse_dandiapi_url(url):
+def _assert_parse_api_url(url):
     st, s, a, aid = parse_dandi_url(url)
-    assert st == "dandiapi"
-    assert s == known_instances["dandi"].dandiapi + "/"
+    assert st == "api"
+    assert s == known_instances["dandi"].api + "/"
     return a, aid
 
 
@@ -62,25 +62,29 @@ def test_parse_dandi_url():
     # new (v1? not yet tagged) web UI, and as it comes from a PR,
     # so we need to provide yet another mapping to stock girder
     assert _assert_parse_girder_url(
-        "https://refactor--gui-dandiarchive-org.netlify.app/#/file-browser/folder/5e9f9588b5c9745bad9f58fe"
+        "https://refactor--gui-dandiarchive-org.netlify.app/#/file-browser"
+        "/folder/5e9f9588b5c9745bad9f58fe"
     ) == ("folder", ["5e9f9588b5c9745bad9f58fe"])
 
     # New DANDI web UI driven by DANDI API.  Again no version assigned/planned!
     # see https://github.com/dandi/dandiarchive/pull/341
-    url1 = "https://deploy-preview-341--gui-dandiarchive-org.netlify.app/#/dandiset/000006/0.200714.1807"
-    assert _assert_parse_dandiapi_url(url1) == (
+    url1 = (
+        "https://deploy-preview-341--gui-dandiarchive-org.netlify.app/"
+        "#/dandiset/000006/0.200714.1807"
+    )
+    assert _assert_parse_api_url(url1) == (
         "dandiset",
         {"dandiset_id": "000006", "version": "0.200714.1807"},
     )
-    assert _assert_parse_dandiapi_url(url1 + "/files") == (
+    assert _assert_parse_api_url(url1 + "/files") == (
         "dandiset",
         {"dandiset_id": "000006", "version": "0.200714.1807"},
     )
-    assert _assert_parse_dandiapi_url(url1 + "/files?location=%2F") == (
+    assert _assert_parse_api_url(url1 + "/files?location=%2F") == (
         "dandiset",
         {"dandiset_id": "000006", "version": "0.200714.1807"},
     )
-    assert _assert_parse_dandiapi_url(url1 + "/files?location=%2Fsub-anm369962%2F") == (
+    assert _assert_parse_api_url(url1 + "/files?location=%2Fsub-anm369962%2F") == (
         "folder",
         {
             "dandiset_id": "000006",
@@ -89,7 +93,7 @@ def test_parse_dandi_url():
         },
     )
     # no trailing / - Yarik considers it to be an item (file)
-    assert _assert_parse_dandiapi_url(url1 + "/files?location=%2Fsub-anm369962") == (
+    assert _assert_parse_api_url(url1 + "/files?location=%2Fsub-anm369962") == (
         "item",
         {
             "dandiset_id": "000006",
@@ -98,7 +102,7 @@ def test_parse_dandi_url():
         },
     )
     # And the hybrid for "drafts" where it still goes by girder ID
-    assert _assert_parse_dandiapi_url(
+    assert _assert_parse_api_url(
         "https://deploy-preview-341--gui-dandiarchive-org.netlify.app/#/dandiset/000027"
         "/draft/files?_id=5f176583f63d62e1dbd06943&_modelType=folder"
     ) == (
@@ -184,7 +188,8 @@ def sleep(duration):
 @pytest.mark.parametrize(
     "url",
     [  # Should go through API
-        "https://deploy-preview-341--gui-dandiarchive-org.netlify.app/#/dandiset/000027/0.200721.2222",
+        "https://deploy-preview-341--gui-dandiarchive-org.netlify.app/"
+        "#/dandiset/000027/0.200721.2222",
         # Good old girder (draft)
         "https://gui.dandiarchive.org/#/dandiset/5f0640a2ab90ac46c4561e4f",
     ],
diff --git a/dandi/tests/test_girder.py b/dandi/tests/test_girder.py
new file mode 100644
index 000000000..37152cdee
--- /dev/null
+++ b/dandi/tests/test_girder.py
@@ -0,0 +1,37 @@
+import pytest
+from ..exceptions import LockingError
+from .. import girder
+
+
+def test_lock_dandiset(local_docker_compose_env):
+    DANDISET_ID = "000001"
+    client = girder.get_client(local_docker_compose_env["instance"].girder)
+    resp = client.get(f"dandi/{DANDISET_ID}/lock/owner")
+    assert resp is None
+    with client.lock_dandiset(DANDISET_ID):
+        resp = client.get(f"dandi/{DANDISET_ID}/lock/owner")
+        assert resp is not None
+    resp = client.get(f"dandi/{DANDISET_ID}/lock/owner")
+    assert resp is None
+
+
+def test_lock_dandiset_error_on_nest(local_docker_compose_env):
+    DANDISET_ID = "000001"
+    client = girder.get_client(local_docker_compose_env["instance"].girder)
+    with client.lock_dandiset(DANDISET_ID):
+        with pytest.raises(LockingError) as excinfo:
+            with client.lock_dandiset(DANDISET_ID):
+                raise AssertionError("This shouldn't be reached")  # pragma: no cover
+        assert str(excinfo.value) == f"Failed to lock dandiset {DANDISET_ID}"
+
+
+def test_lock_dandiset_unlock_within(local_docker_compose_env):
+    DANDISET_ID = "000001"
+    client = girder.get_client(local_docker_compose_env["instance"].girder)
+    unlocked = False
+    with pytest.raises(LockingError) as excinfo:
+        with client.lock_dandiset(DANDISET_ID):
+            client.post(f"dandi/{DANDISET_ID}/unlock")
+            unlocked = True
+    assert unlocked
+    assert str(excinfo.value) == f"Failed to unlock dandiset {DANDISET_ID}"
diff --git a/dandi/tests/test_organize.py b/dandi/tests/test_organize.py
index e2c3b66bd..2166a8213 100644
--- a/dandi/tests/test_organize.py
+++ b/dandi/tests/test_organize.py
@@ -2,7 +2,6 @@
 from glob import glob
 import os.path as op
 import ruamel.yaml
-import yaml
 
 from ..consts import file_operation_modes
 
@@ -14,14 +13,11 @@
     get_obj_id,
     populate_dataset_yml,
 )
-from ..utils import find_files, on_windows
+from ..utils import find_files, on_windows, yaml_load
 from ..pynwb_utils import copy_nwb_file, get_object_id
 import pytest
 
 
-yaml_ruamel = ruamel.yaml.YAML()  # defaults to round-trip if no parameters given
-
-
 def test_sanitize_value():
     # . is not sanitized in extension but elsewhere
     assert _sanitize_value("_.ext", "extension") == "-.ext"
@@ -34,7 +30,7 @@ def test_populate_dataset_yml(tmpdir):
 
     def c():  # shortcut
         with open(path) as f:
-            return yaml.safe_load(f)
+            return yaml_load(f, typ="safe")
 
     path.write("")
     populate_dataset_yml(str(path), [])  # doesn't crash
@@ -51,7 +47,7 @@ def c():  # shortcut
         {"age": 2, "cell_id": "2", "tissue_sample_id": 1, "sex": "F"},
     ]
 
-    # even though we use ruyaml for manipulation, we should assure it is readable
+    # even though we use ruamel for manipulation, we should assure it is readable
     # by regular yaml
     populate_dataset_yml(str(path), metadata)
     assert c() == {
@@ -63,9 +59,9 @@ def c():  # shortcut
     }
 
     # and if we set units and redo -- years should stay unchanged, while other fields change
-    m = yaml_ruamel.load(path.read())
+    m = yaml_load(path.read())
     m["age"]["units"] = "years"
-    yaml_ruamel.dump(m, open(path, "w"))
+    ruamel.yaml.YAML().dump(m, open(path, "w"))
 
     populate_dataset_yml(str(path), metadata[:1])
     assert c() == {
@@ -126,7 +122,7 @@ def test_organize_nwb_test_data(nwb_test_data, tmpdir, clirunner, mode):
     # with @map_to_click_exceptions we loose original str of message somehow
     # although it is shown to the user - checked. TODO - figure it out
     # assert "not containing all" in str(r.exc_info[1])
-    assert r.exit_code != 0, f"Must have aborted since many files lack subject_id"
+    assert r.exit_code != 0, "Must have aborted since many files lack subject_id"
     assert not glob(op.join(outdir, "*")), "no files should have been populated"
 
     r = clirunner.invoke(organize, cmd + ["--invalid", "warn"])
diff --git a/dandi/tests/test_register.py b/dandi/tests/test_register.py
index 3cd919131..c4e948dc1 100644
--- a/dandi/tests/test_register.py
+++ b/dandi/tests/test_register.py
@@ -1,17 +1,11 @@
 import re
 
-import yaml
-
 from ..consts import dandiset_identifier_regex, dandiset_metadata_file
 from ..register import register
+from ..utils import yaml_load
 
 
-def yaml_load(s):
-    obj = yaml.load(s, Loader=yaml.BaseLoader)
-    return obj
-
-
-def test_smoke_metadata_present(local_docker_compose_env, monkeypatch, tmp_path):
+def test_smoke_metadata_present(local_docker_compose_env, tmp_path):
     (tmp_path / dandiset_metadata_file).write_text("{}\n")
     assert (
         register(
@@ -23,7 +17,7 @@ def test_smoke_metadata_present(local_docker_compose_env, monkeypatch, tmp_path)
         is None
     )
     with (tmp_path / dandiset_metadata_file).open() as fp:
-        metadata = yaml_load(fp.read())
+        metadata = yaml_load(fp, typ="base")
     assert metadata
     assert metadata["name"] == "Dandiset Name"
     assert metadata["description"] == "Dandiset Description"
@@ -32,7 +26,7 @@ def test_smoke_metadata_present(local_docker_compose_env, monkeypatch, tmp_path)
     # with the given identifier
 
 
-def test_smoke_metadata_not_present(local_docker_compose_env, monkeypatch, tmp_path):
+def test_smoke_metadata_not_present(local_docker_compose_env, tmp_path):
     assert (
         register(
             "Dandiset Name",
@@ -43,7 +37,7 @@ def test_smoke_metadata_not_present(local_docker_compose_env, monkeypatch, tmp_p
         is None
     )
     with (tmp_path / dandiset_metadata_file).open() as fp:
-        metadata = yaml_load(fp.read())
+        metadata = yaml_load(fp, typ="base")
     assert metadata
     assert metadata["name"] == "Dandiset Name"
     assert metadata["description"] == "Dandiset Description"
diff --git a/dandi/tests/test_upload.py b/dandi/tests/test_upload.py
index 55a5d6b77..5422b7ecc 100644
--- a/dandi/tests/test_upload.py
+++ b/dandi/tests/test_upload.py
@@ -2,12 +2,12 @@
 from shutil import copyfile
 
 import pytest
-import yaml
 
 from .. import girder
 from ..consts import collection_drafts, dandiset_metadata_file
 from ..register import register
 from ..upload import upload
+from ..utils import yaml_load
 
 DANDIFILES_DIR = Path(__file__).with_name("data") / "dandifiles"
 
@@ -31,7 +31,7 @@ def test_upload(local_docker_compose_env, monkeypatch, tmp_path):
         dandi_instance=dandi_instance_id,
     )
     with (tmp_path / dandiset_metadata_file).open() as fp:
-        metadata = yaml.safe_load(fp)
+        metadata = yaml_load(fp, typ="safe")
     dandi_id = metadata["identifier"]
 
     client = girder.get_client(local_docker_compose_env["instance"].girder)
@@ -73,3 +73,43 @@ def test_upload_existing_error(local_docker_compose_env, monkeypatch, tmp_path):
             devel_debug=True,
             existing="error",
         )
+
+
+def test_upload_locks(local_docker_compose_env, mocker, monkeypatch, tmp_path):
+    DIRNAME = "sub-anm369963"
+    FILENAME = "sub-anm369963_ses-20170228.nwb"
+    dandi_instance_id = local_docker_compose_env["instance_id"]
+    (tmp_path / DIRNAME).mkdir(exist_ok=True, parents=True)
+    copyfile(DANDIFILES_DIR / DIRNAME / FILENAME, tmp_path / DIRNAME / FILENAME)
+    register(
+        "Upload Test",
+        "Upload Test Description",
+        dandiset_path=tmp_path,
+        dandi_instance=dandi_instance_id,
+    )
+    monkeypatch.chdir(tmp_path)
+    lockmock = mocker.patch.object(girder.GirderCli, "lock_dandiset")
+    upload(
+        paths=[DIRNAME],
+        dandi_instance=dandi_instance_id,
+        devel_debug=True,
+        existing="error",
+    )
+    lockmock.assert_called()
+    lockmock.return_value.__enter__.assert_called()
+    lockmock.return_value.__exit__.assert_called()
+
+
+def test_upload_unregistered(local_docker_compose_env, monkeypatch, tmp_path):
+    DIRNAME = "sub-anm369963"
+    FILENAME = "sub-anm369963_ses-20170228.nwb"
+    dandi_instance_id = local_docker_compose_env["instance_id"]
+    (tmp_path / dandiset_metadata_file).write_text("identifier: '999999'\n")
+    (tmp_path / DIRNAME).mkdir(exist_ok=True, parents=True)
+    copyfile(DANDIFILES_DIR / DIRNAME / FILENAME, tmp_path / DIRNAME / FILENAME)
+    monkeypatch.chdir(tmp_path)
+    with pytest.raises(ValueError) as excinfo:
+        upload(paths=[DIRNAME], dandi_instance=dandi_instance_id, devel_debug=True)
+    assert str(excinfo.value) == (
+        f"There is no 999999 in {collection_drafts}. Did you use 'dandi register'?"
+    )
diff --git a/dandi/tests/test_utils.py b/dandi/tests/test_utils.py
index 279ebf5bd..db4d6270d 100644
--- a/dandi/tests/test_utils.py
+++ b/dandi/tests/test_utils.py
@@ -1,14 +1,18 @@
 import inspect
 import os.path as op
 import time
-import datetime
 import pytest
+import responses
+from .. import __version__
+from ..consts import dandi_instance, known_instances
+from ..exceptions import BadCliVersionError, CliVersionTooOldError
 from ..utils import (
     ensure_datetime,
     ensure_strtime,
     find_files,
     flatten,
     flattened,
+    get_instance,
     get_utcnow_datetime,
     is_same_time,
     on_windows,
@@ -144,3 +148,171 @@ def test_flatten():
 )
 def test_remap_dict(from_, revmapping, to):
     assert remap_dict(from_, revmapping) == to
+
+
+@responses.activate
+def test_get_instance_dandi():
+    responses.add(
+        responses.GET,
+        "https://dandiarchive.org/server-info",
+        json={
+            "version": "1.0.0",
+            "cli-minimal-version": "0.5.0",
+            "cli-bad-versions": [],
+            "services": {
+                "girder": {"url": "https://girder.dandi"},
+                "webui": {"url": "https://gui.dandi"},
+                "api": {"url": "https://publish.dandi/api"},
+                "jupyterhub": {"url": "https://hub.dandi"},
+            },
+        },
+    )
+    assert get_instance("dandi") == dandi_instance(
+        girder="https://girder.dandi",
+        gui="https://gui.dandi",
+        redirector="https://dandiarchive.org",
+        api="https://publish.dandi/api",
+    )
+
+
+@responses.activate
+def test_get_instance_url():
+    responses.add(
+        responses.GET,
+        "https://example.dandi/server-info",
+        json={
+            "version": "1.0.0",
+            "cli-minimal-version": "0.5.0",
+            "cli-bad-versions": [],
+            "services": {
+                "girder": {"url": "https://girder.dandi"},
+                "webui": {"url": "https://gui.dandi"},
+                "api": {"url": "https://publish.dandi/api"},
+                "jupyterhub": {"url": "https://hub.dandi"},
+            },
+        },
+    )
+    assert get_instance("https://example.dandi/") == dandi_instance(
+        girder="https://girder.dandi",
+        gui="https://gui.dandi",
+        redirector="https://example.dandi/",
+        api="https://publish.dandi/api",
+    )
+
+
+@responses.activate
+def test_get_instance_cli_version_too_old():
+    responses.add(
+        responses.GET,
+        "https://example.dandi/server-info",
+        json={
+            "version": "1.0.0",
+            "cli-minimal-version": "99.99.99",
+            "cli-bad-versions": [],
+            "services": {
+                "girder": {"url": "https://girder.dandi"},
+                "webui": {"url": "https://gui.dandi"},
+                "api": {"url": "https://publish.dandi/api"},
+                "jupyterhub": {"url": "https://hub.dandi"},
+            },
+        },
+    )
+    with pytest.raises(CliVersionTooOldError) as excinfo:
+        get_instance("https://example.dandi/")
+    assert str(excinfo.value) == (
+        f"Client version {__version__} is too old!"
+        "  Server requires at least version 99.99.99"
+    )
+
+
+@responses.activate
+def test_get_instance_bad_cli_version():
+    responses.add(
+        responses.GET,
+        "https://example.dandi/server-info",
+        json={
+            "version": "1.0.0",
+            "cli-minimal-version": "0.5.0",
+            "cli-bad-versions": [__version__],
+            "services": {
+                "girder": {"url": "https://girder.dandi"},
+                "webui": {"url": "https://gui.dandi"},
+                "api": {"url": "https://publish.dandi/api"},
+                "jupyterhub": {"url": "https://hub.dandi"},
+            },
+        },
+    )
+    with pytest.raises(BadCliVersionError) as excinfo:
+        get_instance("https://example.dandi/")
+    assert str(excinfo.value) == (
+        f"Client version {__version__} is rejected by server!"
+        f"  Server requires at least version 0.5.0 (but not {__version__})"
+    )
+
+
+@responses.activate
+def test_get_instance_id_bad_response():
+    responses.add(
+        responses.GET,
+        "https://dandiarchive.org/server-info",
+        body="404 -- not found",
+        status=404,
+    )
+    assert get_instance("dandi") is known_instances["dandi"]
+
+
+@responses.activate
+def test_get_instance_known_url_bad_response():
+    responses.add(
+        responses.GET,
+        "https://dandiarchive.org/server-info",
+        body="404 -- not found",
+        status=404,
+    )
+    assert get_instance("https://dandiarchive.org") is known_instances["dandi"]
+
+
+@responses.activate
+def test_get_instance_unknown_url_bad_response():
+    responses.add(
+        responses.GET,
+        "https://dandi.nil/server-info",
+        body="404 -- not found",
+        status=404,
+    )
+    with pytest.raises(RuntimeError) as excinfo:
+        get_instance("https://dandi.nil")
+    assert str(excinfo.value) == (
+        "Could not retrieve server info from https://dandi.nil,"
+        " and client does not recognize URL"
+    )
+
+
+def test_get_instance_id_no_redirector():
+    assert get_instance("local-girder-only") is known_instances["local-girder-only"]
+
+
+@responses.activate
+def test_get_instance_bad_version_from_server():
+    responses.add(
+        responses.GET,
+        "https://example.dandi/server-info",
+        json={
+            "version": "1.0.0",
+            "cli-minimal-version": "foobar",
+            "cli-bad-versions": [],
+            "services": {
+                "girder": {"url": "https://girder.dandi"},
+                "webui": {"url": "https://gui.dandi"},
+                "api": {"url": "https://publish.dandi/api"},
+                "jupyterhub": {"url": "https://hub.dandi"},
+            },
+        },
+    )
+    with pytest.raises(ValueError) as excinfo:
+        get_instance("https://example.dandi/")
+    assert str(excinfo.value).startswith(
+        "https://example.dandi/ returned an incorrectly formatted version;"
+        " please contact that server's administrators: "
+    )
+    assert "foobar" in str(excinfo.value)
diff --git a/dandi/upload.py b/dandi/upload.py
index edac0c7c2..9050f644a 100644
--- a/dandi/upload.py
+++ b/dandi/upload.py
@@ -8,12 +8,11 @@
 
 from .cli.command import lgr
 from . import __version__
-from .utils import ensure_datetime, ensure_strtime
+from .utils import ensure_datetime, ensure_strtime, get_instance
 from .consts import (
     collection_drafts,
     dandiset_identifier_regex,
     dandiset_metadata_file,
-    known_instances,
     metadata_digests,
 )
 
@@ -73,13 +72,6 @@ def upload(
             f"into a collection directly."
         )
 
-    # TODO: that the folder already exists
-    if False:
-        raise ValueError(
-            f"There is no {girder_top_folder} in {girder_collection}. "
-            f"Did you use 'dandi register'?"
-        )
-
     import multiprocessing
     from . import girder
     from .pynwb_utils import ignore_benign_pynwb_warnings, get_object_id
@@ -91,7 +83,7 @@ def upload(
 
     ignore_benign_pynwb_warnings()  # so validate doesn't whine
 
-    client = girder.get_client(known_instances[dandi_instance].girder)
+    client = girder.get_client(get_instance(dandi_instance).girder)
 
     try:
         collection_rec = girder.ensure_collection(client, girder_collection)
@@ -108,6 +100,14 @@ def upload(
 
     lgr.debug("Working with collection %s", collection_rec)
 
+    try:
+        girder.lookup(client, girder_collection, path=girder_top_folder)
+    except girder.GirderNotFound:
+        raise ValueError(
+            f"There is no {girder_top_folder} in {girder_collection}. "
+            f"Did you use 'dandi register'?"
+        )
+
     #
     # Treat paths
     #
@@ -505,7 +505,7 @@ def upload_agg(*ignored):
     rec_fields = ["path", "size", "errors", "upload", "status", "message"]
     out = pyout.Tabular(style=pyout_style, columns=rec_fields)
 
-    with out:
+    with out, client.lock_dandiset(dandiset.identifier):
         for path in paths:
             while len(process_paths) >= 10:
                 lgr.log(2, "Sleep waiting for some paths to finish processing")
diff --git a/dandi/utils.py b/dandi/utils.py
index a8d46512d..d0e0e3170 100644
--- a/dandi/utils.py
+++ b/dandi/utils.py
@@ -1,5 +1,6 @@
 import datetime
 import inspect
+import io
 import itertools
 import os
 import os.path as op
@@ -10,6 +11,14 @@
 
 from pathlib import Path
 
+import requests
+import ruamel.yaml
+from semantic_version import Version
+
+from . import __version__
+from .consts import dandi_instance, known_instances, known_instances_rev
+from .exceptions import BadCliVersionError, CliVersionTooOldError
+
 if sys.version_info[:2] < (3, 7):
     import dateutil.parser
 
@@ -380,9 +389,31 @@ def yaml_dump(rec):
     to assure proper formatting on versions of pyyaml before
     5.1: https://github.com/yaml/pyyaml/pull/256
     """
-    import yaml
+    yaml = ruamel.yaml.YAML(typ="safe")
+    yaml.default_flow_style = False
+    out = io.StringIO()
+    yaml.dump(rec, out)
+    return out.getvalue()
 
-    return yaml.safe_dump(rec, default_flow_style=False)
+
+def yaml_load(f, typ=None):
+    """
+    Load YAML source from a file or string.
+
+    Parameters
+    ----------
+    f: str or IO[str]
+      The YAML source to load
+    typ: str, optional
+      The value of `typ` to pass to `ruamel.yaml.YAML`.  May be "rt" (default),
+      "safe", "unsafe", or "base"
+
+    Returns
+    -------
+    Any
+      The parsed YAML value
+    """
+    return ruamel.yaml.YAML(typ=typ).load(f)
 
 
 #
@@ -512,3 +543,51 @@ def delayed(*args, **kwargs):
     import joblib
 
     return joblib.delayed(*args, **kwargs)
+
+
+def get_instance(dandi_instance_id):
+    if dandi_instance_id.lower().startswith(("http://", "https://")):
+        redirector_url = dandi_instance_id
+        dandi_id = known_instances_rev.get(redirector_url)
+        if dandi_id is not None:
+            instance = known_instances[dandi_id]
+        else:
+            instance = None
+    else:
+        instance = known_instances[dandi_instance_id]
+        redirector_url = instance.redirector
+        if redirector_url is None:
+            return instance
+    try:
+        r = requests.get(redirector_url.rstrip("/") + "/server-info")
+        r.raise_for_status()
+    except Exception as e:
+        lgr.warning("Request to %s failed (%s)", redirector_url, str(e))
+        if instance is not None:
+            lgr.warning("Using hard-coded URLs")
+            return instance
+        else:
+            raise RuntimeError(
+                f"Could not retrieve server info from {redirector_url},"
+                " and client does not recognize URL"
+            )
+    server_info = r.json()
+    try:
+        minversion = Version(server_info["cli-minimal-version"])
+        bad_versions = [Version(v) for v in server_info["cli-bad-versions"]]
+    except ValueError as e:
+        raise ValueError(
+            f"{redirector_url} returned an incorrectly formatted version;"
+            f" please contact that server's administrators: {e}"
+        )
+    our_version = Version(__version__)
+    if our_version < minversion:
+        raise CliVersionTooOldError(our_version, minversion, bad_versions)
+    if our_version in bad_versions:
+        raise BadCliVersionError(our_version, minversion, bad_versions)
+    return dandi_instance(
+        girder=server_info["services"]["girder"]["url"],
+        gui=server_info["services"]["webui"]["url"],
+        redirector=redirector_url,
+        api=server_info["services"]["api"]["url"],
+    )
diff --git a/dandi/validate.py b/dandi/validate.py
index 43fc28557..a752ef4f8 100644
--- a/dandi/validate.py
+++ b/dandi/validate.py
@@ -1,9 +1,8 @@
 import os.path as op
 from .consts import dandiset_metadata_file
-import yaml
 
 from .pynwb_utils import validate as pynwb_validate, validate_cache
-from .utils import find_dandi_files
+from .utils import find_dandi_files, yaml_load
 from .metadata import get_metadata
 
 
@@ -42,7 +41,7 @@ def validate_file(filepath):
 def validate_dandiset_yaml(filepath):
     """Validate dandiset.yaml"""
     with open(filepath) as f:
-        meta = yaml.safe_load(f)
+        meta = yaml_load(f, typ="safe")
     return _check_required_fields(meta, _required_dandiset_metadata_fields)
 
 
diff --git a/setup.cfg b/setup.cfg
index ddc2c139a..797e4e7db 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -40,10 +40,10 @@ install_requires =
     click-didyoumean
     etelemetry >= 0.2.0
     joblib
-    pyout
+    pyout != 0.6.0
     humanize
-    pyyaml
-    ruamel.yaml
+    requests ~= 2.20
+    ruamel.yaml >=0.15, <1
     keyring
     keyrings.alt
     python-dateutil;  python_version < "3.7"
@@ -68,10 +68,10 @@ style =
     pre-commit
 test =
     coverage
-    mock
     pytest
     pytest-cov
-    requests ~= 2.20
+    pytest-mock
+    responses
 all =
     #%(doc)s
     %(extensions)s
@@ -87,7 +87,6 @@ max-line-length = 100
 #ignore = D100,D101,D102,D103,D104,D105,D200,D201,D202,D204,D205,D208,D209,D210,D300,D301,D400,D401,D403,E24,E121,E123,E126,E226,E266,E402,E704,E731,F821,I100,I101,I201,N802,N803,N804,N806,W503,W504,W605
 ignore = E203,W503
 exclude =
-    *test*
     *sphinx*
     dandi/externals/*
     */__init__.py
diff --git a/tox.ini b/tox.ini
index 6ea8ad288..1bf601172 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,10 +4,9 @@ envlist = lint,py3
 [testenv]
 extras = test
 commands =
-    # Using pytest-cov leaves a bunch of .coverage.$HOSTNAME.#.# files lying
-    # around for some reason
-    #python -m pytest -s -v --cov=dandi dandi
-    coverage run -m pytest -v dandi
+    # Using pytest-cov instead of using coverage directly leaves a bunch of
+    # .coverage.$HOSTNAME.#.# files lying around for some reason
+    coverage run -m pytest -v {posargs} dandi
     coverage combine
     coverage report
 
@@ -24,6 +23,7 @@ filterwarnings =
     error
     ignore:No cached namespaces found .*:UserWarning
     ignore:ignoring namespace '.*' because it already exists:UserWarning
+    ignore::DeprecationWarning:responses
 
 [coverage:run]
 parallel = True