out_kafka_rest: Document usage of Message_Key_Field in sending messages to Kafka Rest

[TechBRSavvy]

Documents changes posted fluent/fluent-bit#7813

Summary by CodeRabbit

• Documentation
  • Updated Kafka REST proxy output plugin documentation with a new message_key_field configuration parameter. Users can specify which record field serves as the message key, with automatic fallback to message_key configuration when the specified field is unavailable.

[eschabell]

@esmerel can you please review and check on the conflicts?

[esmerel]

@esmerel can you please review and check on the conflicts?

fixed!

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c2dcde5b-831b-489a-8441-441c18cbd5df

📥 Commits

Reviewing files that changed from the base of the PR and between fb56bf7 and fae7cb7.

📒 Files selected for processing (1)

• pipeline/outputs/kafka-rest-proxy.md

📝 Walkthrough

Walkthrough

This PR documents a new message_key_field parameter for the Kafka REST proxy output plugin. The parameter is added to the configuration table with documentation explaining its precedence over message_key, and the fluent-bit.conf example block is reformatted for consistency.

Changes

Kafka REST Proxy message_key_field Documentation

Layer / File(s)	Summary
Configuration parameter documentation pipeline/outputs/kafka-rest-proxy.md	message_key_field parameter is added to the plugin configuration table with documentation of its purpose and precedence behavior when fallback to message_key occurs.
Configuration example formatting pipeline/outputs/kafka-rest-proxy.md	The fluent-bit.conf example block is reformatted and realigned while preserving the same example output configuration settings.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• fluent/fluent-bit-docs#2437: Both PRs modify Kafka REST proxy configuration documentation in the same file, with this PR adding message_key_field and the other PR standardizing the parameter table structure.

Suggested labels

5.0

Poem

🐰 A message key field, so fresh and new,
Cascades through Kafka with precedence true,
When set, it takes the lead with grace,
Falls back to message_key's place,
Docs aligned, examples too—
Config now shines for all to view! 📝

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: documentation for the Message_Key_Field parameter in the Kafka REST proxy output plugin.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[eschabell]

@TechBRSavvy fixed the conflicts.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pipeline/outputs/kafka-rest-proxy.md`:
- Line 15: The Markdown table row incorrectly merges two parameters into one;
split the combined row into two separate table rows for `message_key_field` and
`partition` so each parameter has its own description and default value. Locate
the merged cell referencing `message_key_field` and `partition` and create one
row: `message_key_field` with its description ("If set, the value of
`message_key_field` in the record indicates the message key. If not set nor
found in the record, `message_key` will be used (if set).") and default
(`_none_`), and a second row: `partition` with its description ("Optional
partition number.") and default (`-1`), ensuring proper pipe-separated Markdown
table syntax and column alignment.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f0bbf98f-acb6-409b-91fc-b4f7f4892cfd

📥 Commits

Reviewing files that changed from the base of the PR and between 5231934 and fb56bf7.

📒 Files selected for processing (1)

• pipeline/outputs/kafka-rest-proxy.md

[eschabell]

@TechBRSavvy now just waiting on code PR merging.