Contributing Code Changes (DRAFT)

This document is a work in progress, please see Patch submission and review in the meantime.

Overview

Please review Kafka's Contributing page before proposing a code change. This section documents how to do so.

JIRA

Generally, Kafka uses:

• JIRA to track logical issues, including bugs and improvements
• Confluence for documentation and Kafka Improvement Proposals
• Github pull requests to manage the review and merge of specific code changes
  

That is, JIRA and Confluence are used to describe what should be fixed or changed, and high-level approaches, and pull requests describe how to implement that change in the project's source code.

1. Find the existing Kafka JIRA that the change pertains to.

1. Do not create a new JIRA if creating a change to address an existing issue in JIRA; add to the existing discussion and work instead

2. Look for existing pull requests that are linked from the JIRA, to understand if someone is already working on the JIRA

2. If the change is new, then it usually needs a new JIRA. However, trivial changes, where "what should change" is virtually the same as "how it should change" do not require a JIRA. Example: "Fix typos in Foo scaladoc"

3. If required, create a new JIRA:

1. Provide a descriptive Title. "Update web UI" or "Problem in scheduler" is not sufficient. "Kafka support fails to handle empty queue in cluster mode" is good.

2. Write a detailed Description. For bug reports, this should ideally include a short reproduction of the problem. For new features, it may include a design document (or a Kafka Improvement Proposal if it's a major change).

3. Set required fields.

4. Do not include a patch file; pull requests are used to propose the actual change.

4. If the change is a large change, consider inviting discussion on the issue at dev@kafka.apache.org first before proceeding to implement the change.

Pull Request

1. Fork the Github repository at http://github.com/apache/kafka if you haven't already

2. Clone your fork, create a new branch, push commits to the branch (review the Kafka Coding Guidelines, if you haven't already).

3. Consider whether documentation or tests need to be added or updated as part of the change, and add them as needed.

4. Run all tests as described in the project's README.
   

5. Open a pull request against the trunk branch of apache/kafka. (Only in special cases would the PR be opened against other branches.)

1. The PR title should be of the form [KAFKA-xxxx] Title, where KAFKA-xxxx is the relevant JIRA id and Title may be the JIRA's title or a more specific title describing the PR itself.

2. If the pull request is still a work in progress, and so is not ready to be merged, but needs to be pushed to Github to facilitate review, then add [WIP] after the JIRA id.

3. Consider identifying committers or other contributors who have worked on the code being changed. Find the file(s) in Github and click "Blame" to see a line-by-line annotation of who changed the code last and check the Maintainers page. You can add @username in the PR description to ping them immediately.

4. Please state that the contribution is your original work and that you license the work to the project under the project's open source license.

6. The related JIRA, if any, will be marked as "In Progress" and your pull request will automatically be linked to it.

The following steps are planned, but not yet configured.

1. The Jenkins automatic pull request builder will test your changes

1. If it is your first contribution, Jenkins will wait for confirmation before building your code and post "Can one of the admins verify this patch?"

2. A committer can authorize testing with a comment like "ok to test"

3. A committer can automatically allow future pull requests from a contributor to be tested with a comment like "Jenkins, add to whitelist"

2. Once ready, the test results will be posted on the pull request, along with a link to the full results on Jenkins.

3. Watch for the results, and investigate and fix failures promptly

1. Fixes can simply be pushed to the same branch from which you opened your pull request

2. Jenkins will automatically re-test when new commits are pushed

3. If the tests failed for reasons unrelated to the change (e.g. Jenkins outage), then a committer can request a re-test with "Jenkins, retest this please". Ask if you need a test restarted.

The Review Process

• Other reviewers, including committers, may comment on the changes and suggest modifications. Changes can be added by simply pushing more commits to the same branch.

• Lively, polite, rapid technical debate is encouraged from everyone in the community. The outcome may be a rejection of the entire change.

• Reviewers can indicate that a change looks suitable for merging with a comment such as: "I think this patch looks good". Kafka uses the LGTM convention for indicating the strongest level of technical sign-off on a patch: simply comment with the word "LGTM". It specifically means: "I've looked at this thoroughly and take as much ownership as if I wrote the patch myself". If you comment LGTM you will be expected to help with bugs or follow-up issues on the patch. Consistent, judicious use of LGTMs is a great way to gain credibility as a reviewer with the broader community.

• Sometimes, other changes will be merged which conflict with your pull request's changes. The PR can't be merged until the conflict is resolved. This can be resolved with "git fetch origin" followed by "git rebase origin/trunk" and resolving the conflicts by hand, then pushing the result to your branch.

• Try to be responsive to the discussion rather than let days pass between replies

Closing Your Pull Request / JIRA

• If a change is accepted, it will be merged and the pull request will automatically be closed, along with the associated JIRA if any

• Note that in the rare case you are asked to open a pull request against a branch besides trunk, that you will actually have to close the pull request manually

• The JIRA will be Assigned to the primary contributor to the change as a way of giving credit. If the JIRA isn't closed and/or Assigned promptly, comment on the JIRA.

• If your pull request is ultimately rejected, please close it promptly

• ... because committers can't close PRs directly

• Pull requests will be automatically closed by an automated process at Apache after about a week if a committer has made a comment like "mind closing this PR?" This means that the committer is specifically requesting that it be closed.

• If a pull request has gotten little or no attention, consider improving the description or the change itself and ping likely reviewers again after a few days. Consider proposing a change that's easier to include, like a smaller and/or less invasive change.

• If a pull request is closed because it is deemed not the right approach to resolve a JIRA, then leave the JIRA open. However if the review makes it clear that the issue identified in the JIRA is not going to be resolved by any pull request (not a problem, won't fix) then also resolve the JIRA.