out_azure_blob: add log_key option

[tomekwilk]

This PR is based on PR #3668 but addresses Azure blob storage. The azure_blob plugin was modify to accept 'log_key' option. By default the entire log record is sent to storage. When 'log_key' option is specified in the output plugin configuration, then only the value of the key is sent to the storage blob.

Addresses #9721

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

Documentation

• Documentation required for this feature

Doc PR fluent/fluent-bit-docs#1540

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

By default the entire record is sent to azure blob storage. Here is an example of a sample configuration and default output

Configuration

[SERVICE]
    flush     1
    log_level info

[INPUT]
    name      dummy
    dummy     {"name": "Fluent Bit", "year": 2020}
    samples   1
    tag       var.log.containers.app-default-96cbdef2340.log

[OUTPUT]
    name                  azure_blob
    match                 *
    account_name          twilk123
    shared_key            <snip>
    path                  kubernetes
    container_name        test-container
    auto_create_container on
    tls                   on

Record without log_key
{"@timestamp":"2025-01-02T16:56:02.906357Z","name":"Fluent Bit","year":2020}

if the 'log_key' is specified then only the specific key value is sent to azure blob storage

Sample configuration with log_key

[SERVICE]
    flush     1
    log_level info

[INPUT]
    name      dummy
    dummy     {"name": "Fluent Bit", "year": 2020}
    samples   1
    tag       var.log.containers.app-default-96cbdef2340.log

[OUTPUT]
    name                  azure_blob
    match                 *
    account_name          twilk123
    shared_key            <snip>
    path                  kubernetes
    container_name        test-container
    auto_create_container on
    tls                   on
    log_key               name

Record with log_key set to name
Fluent Bit

Example Valgrind output

root@fluent-bit:/tmp# valgrind ./fluent-bit -c azure.conf
==3022== Memcheck, a memory error detector
==3022== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==3022== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==3022== Command: ./fluent-bit -c azure.conf
==3022==
Fluent Bit v3.2.3
* Copyright (C) 2015-2024 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _           _____  _____
|  ___| |                | |   | ___ (_) |         |____ |/ __  \
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __   / /`' / /'
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / /   \ \  / /
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /.___/ /./ /___
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/ \____(_)_____/


[2025/01/02 19:56:50] [ info] [fluent bit] version=3.2.3, commit=addf261e8c, pid=3022
[2025/01/02 19:56:50] [ info] [storage] ver=1.5.2, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/01/02 19:56:50] [ info] [simd    ] disabled
[2025/01/02 19:56:50] [ info] [cmetrics] version=0.9.9
[2025/01/02 19:56:50] [ info] [ctraces ] version=0.5.7
[2025/01/02 19:56:51] [ info] [output:azure_blob:azure_blob.0] initializing worker
[2025/01/02 19:56:50] [ info] [input:dummy:dummy.0] initializing
[2025/01/02 19:56:51] [ info] [output:azure_blob:azure_blob.0] worker #0 started
[2025/01/02 19:56:50] [ info] [input:dummy:dummy.0] storage_strategy='memory' (memory only)
[2025/01/02 19:56:51] [ info] [output:azure_blob:azure_blob.0] account_name=twilk123, container_name=test-container, blob_type=appendblob, emulator_mode=no, endpoint=twilk123.blob.core.windows.net, auth_type=key
[2025/01/02 19:56:51] [ info] [sp] stream processor started
[2025/01/02 19:56:54] [ info] [output:azure_blob:azure_blob.0] container 'test-container' already exists
[2025/01/02 19:56:54] [ info] [output:azure_blob:azure_blob.0] content uploaded successfully:
[2025/01/02 19:56:54] [ info] [output:azure_blob:azure_blob.0] blob id (null) committed successfully
^C[2025/01/02 19:57:03] [engine] caught signal (SIGINT)
[2025/01/02 19:57:03] [ warn] [engine] service will shutdown in max 5 seconds
[2025/01/02 19:57:03] [ info] [input] pausing dummy.0
[2025/01/02 19:57:03] [ info] [engine] service has stopped (0 pending tasks)
[2025/01/02 19:57:03] [ info] [input] pausing dummy.0
[2025/01/02 19:57:03] [ info] [output:azure_blob:azure_blob.0] thread worker #0 stopping...
[2025/01/02 19:57:03] [ info] [output:azure_blob:azure_blob.0] initializing worker
[2025/01/02 19:57:03] [ info] [output:azure_blob:azure_blob.0] thread worker #0 stopped
==3022==
==3022== HEAP SUMMARY:
==3022==     in use at exit: 0 bytes in 0 blocks
==3022==   total heap usage: 17,894 allocs, 17,894 frees, 2,471,158 bytes allocated
==3022==
==3022== All heap blocks were freed -- no leaks are possible
==3022==
==3022== For lists of detected and suppressed errors, rerun with: -s
==3022== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Addresses #9721