kafka: verify replication-factor when need to create the topic (#5715)

[ti-chi-bot]

This is an automated cherry-pick of #5715

What problem does this PR solve?

Issue Number: close #5720

Kafka sink Verify returned immediately after fetching metadata when the target topic already existed. This skipped NewEventEncoder, so encoder-owned checks—most notably Avro Schema Registry connectivity—were not run.

replication-factor is a topic creation option. The previous path could validate it even when the topic already existed or automatic topic creation was disabled, although TiCDC would not use it in either case.

What is changed and how it works?

• Preserve the initialization order from master and remove the early return for an existing topic. Encoder initialization now runs after Kafka verification for both existing and missing topics.
• Skip replication-factor validation and validate-only topic creation for existing topics.
• For a missing topic:
  • report that the topic does not exist when automatic topic creation is disabled;
  • when required-acks=all, compare the configured replication factor with the broker min.insync.replicas;
  • use Kafka's validate-only CreateTopic request during sink verification.
• Run the same replication-factor validation immediately before runtime topic creation, including dynamically routed topics.
• Reject a non-positive replication-factor while applying sink options.
• Keep broker configuration lookup local to the creation check; no existing-topic replication factor is fetched or validated.

Check List

Tests

• Unit test

  go test --tags=intest ./pkg/sink/kafka ./downstreamadapter/sink/kafka ./downstreamadapter/sink/topicmanager -count=1

Questions

Will it cause performance regression or break compatibility?

No. This changes verification and topic-creation validation only. It does not change a public API or protocol.

Do you need to update user documentation, design documentation, or monitoring documentation?

No.

Release note

None

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be LGTMed and approved by the reviewers firstly.
2. For pull requests to TiDB-x branches, it must have no failed tests.
3. AFTER it has lgtm and approved labels, please wait for the cherry-pick merging approval from triage owners.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[ti-chi-bot]

@3AceShowHand This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign kennytm for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 300cc9ac-b2ca-4bd9-93a6-e66ab604412f

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[3AceShowHand]

close by #5811