Deprecate fleet.agent.logging.level attribute (#3195)

Deprecate the fleet.agent.logging.level attribute and rely on the top
level logging.* attributes instead. Add a unit test to make sure that
command line overrides are respected.

Author: michel-laterman

changelog/fragments/1703700493-deprecate-fleet.agent.logging.level.yaml

@@ -0,0 +1,35 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: bug-fix
+
+# Change summary; a 80ish characters long description of the change.
+summary: deprecate fleet.agent.logging.level
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+description: |
+  Deprecate the fleet.agent.logging.level attribute and rely only on the
+  top level logging.* attributes to control fleet-server logging. Add a
+  unit test to ensure logging flags are parsed correctly.
+
+# Affected component; a word indicating the component this changeset affects.
+component:
+
+# PR URL; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+#pr: https://github.com/owner/repo/1234
+
+# Issue URL; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+issue: 3126

cmd/fleet/flag_test.go

@@ -0,0 +1,59 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package fleet
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/elastic/fleet-server/v7/internal/pkg/build"
+	"github.com/elastic/fleet-server/v7/internal/pkg/config"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAgentModeFlag(t *testing.T) {
+	tests := []struct {
+		name   string
+		flags  []string
+		expect func() *config.Config
+	}{{
+		name:  "no flags",
+		flags: []string{},
+		expect: func() *config.Config {
+			cfg := &config.Config{}
+			cfg.InitDefaults()
+			cfg.Output.Elasticsearch.InitDefaults() // NOTE this is implicitly called when ucfg parses the top level cfg object, but we need to explicitly call it for testing.
+			return cfg
+		},
+	}, {
+		name:  "debug log flag",
+		flags: []string{"E logging.level=debug"}, // flag is the k:v separated by a space, key does not have the "-" prefix
+		expect: func() *config.Config {
+			cfg := &config.Config{}
+			cfg.InitDefaults()
+			cfg.Output.Elasticsearch.InitDefaults()
+			cfg.Logging.Level = "debug"
+			return cfg
+		},
+	}}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			cmd := NewCommand(build.Info{})
+			for _, flag := range tc.flags {
+				arr := strings.Split(flag, " ")
+				err := cmd.Flags().Set(arr[0], arr[1])
+				require.NoError(t, err)
+			}
+
+			cfgObj := cmd.Flags().Lookup("E").Value.(*config.Flag) //nolint:errcheck // same as in main
+			cfgCLI := cfgObj.Config()
+			cfg, err := config.FromConfig(cfgCLI)
+			require.NoError(t, err)
+			require.Equal(t, tc.expect(), cfg)
+		})
+	}
+}

fleet-server.reference.yml

@@ -50,7 +50,8 @@ fleet:
     id: fleet-server-agent-idv
 #    # version is the version of the elastic-agent instance
 #    version:
-#    # agent logging level may also be specified in top level logging config
+#    # specify logging level
+#    # deprecated: Use the top level logging.* attributes instead.
 #    logging.level: info
 #  host:
 #    id:

internal/pkg/config/fleet.go

@@ -11,9 +11,8 @@ import (
 	"github.com/rs/zerolog"
 )
 
-const defaultLevel = "info"
-
 // AgentLogging is the log level set on the Agent.
+// deprectated: Use top level `logging.*` attributes instead.
 type AgentLogging struct {
 	Level string `config:"level"`
 }

internal/pkg/config/logging.go

@@ -11,6 +11,8 @@ import (
 	"github.com/rs/zerolog"
 )
 
+const defaultLevel = "info"
+
 // LoggingFiles configuration for the logging file output.
 type LoggingFiles struct {
 	Path            string        `config:"path"`

internal/pkg/logger/logger.go

@@ -101,16 +101,10 @@ func Init(cfg *config.Config, svcName string) (*Logger, error) {
 }
 
 func levelChanged(cfg *config.Config) bool {
-	if cfg.Fleet.Agent.Logging.LogLevel() != zerolog.GlobalLevel() {
-		return true
-	}
 	return level(cfg) != zerolog.GlobalLevel()
 }
 
 func level(cfg *config.Config) zerolog.Level {
-	if cfg.Fleet.Agent.Logging.Level != "" {
-		return cfg.Fleet.Agent.Logging.LogLevel()
-	}
 	return cfg.Logging.LogLevel()
 }
 

internal/pkg/server/agent.go

@@ -404,9 +404,6 @@ func (a *Agent) configFromUnits() (*config.Config, error) {
 			"agent": map[string]interface{}{
 				"id":      agentID,
 				"version": agentVersion,
-				"logging": map[string]interface{}{
-					"level": logLevel.String(),
-				},
 			},
 		},
 		"output": map[string]interface{}{