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Gerrit, Jenkins, and GitHub

For a quick reference, please see GerritWorkflow instead.

GitHub is a resource for managing Git code repositories and interacting with other developers. Jenkins is used to continuously test all of the components of OpenStack to ensure functionality and to verify that each change to the code base works as intended. Gerrit is a code review system originally developed for use by the Android Open Source Project and allows us to build a workflow where every change is peer-reviewed and tested by Jenkins before being merged into the main repository.

After making a change in their local Git repository, developers can easily push that change to Gerrit as a proposed change for the project. Jenkins will automatically run functional tests on the code and provide feedback on the change in Gerrit. Any OpenStack developer can provide feedback (in the form of a comment, or even line-by-line annotations) using Gerrit, and the core developers of the project can indicate whether they approve of the patch as is, or would like to see changes before it is integrated. Once patches are merged by Gerrit, the repository is pushed to the canonical public repository on GitHub.

Using Gerrit

The next sections describe how Gerrit fits into the developer workflow.

Gerrit Accounts

Gerrit lives at https://review.openstack.org/. Visit and click the Sign In link at the top-right corner of the page. Log in with your Launchpad ID.

Because Gerrit uses Launchpad OpenID single sign-on, you won't need a separate password for Gerrit, and once you log in to one of Launchpad, Gerrit, or Jenkins, you won't have to enter your password for the others.

Gerrit accounts are automatically synchronized with Launchpad, so your Gerrit account should already have the same username, full name, email address, ssh keys, and group membership.

Some information in Launchpad is not publicly available and so may not be copied over. The first time you log into Gerrit, you should click the Settings link at the top of the page, and then make sure that your Contact Information, SSH Public Keys, and Groups look correct. If not, please register your email address and SSH keys. If your group membership is not correct, please email openstack-ci-admins@lists.launchpad.net .

Ensure that you have run these steps to let git know about your email address:

git config --global user.name "Firstname Lastname"
git config --global user.email "your_email@youremail.com"

Setting up Git for Use with Gerrit

For a more comprehensive look at using Gerrit, see the Gerrit manual.

Change-Id Hook

Gerrit uses a Change-Id footer in commits so that it can link Git commits to changes stored in its database. When you upload a revised change (to correct a problem or respond to code review comments), Gerrit will use the Change-Id footer to attach the commit as a new patchset on the existing gerrit change. This works best if the Change-Id is already in the original commit message, before it is even sent to Gerrit.

"git review" installs a commit hook into your repository that automatically adds Change-Id lines to your commits..

The Gerrit manual goes into more detail about change IDs.

Install the git-review tool, which is the tool OpenStack uses to simplify submission of reviews to Gerrit.

sudo pip install git-review

Pushing Changes from Git

Simply running git review should be sufficient to push your changes to Gerrit, assuming your repository is set up as described above, you don't need to read the rest of this section unless you want to use an alternate workflow.

If you want to push your changes without using git-review, you can push changes to gerrit like you would any other git repository, using the following syntax (assuming "gerrit" is configured as a remote repository):

git push gerrit HEAD:refs/for/$BRANCH[/$TOPIC]

Where $BRANCH is the name of the Gerrit branch to push to (usually "master"), and you may optionally specify a Gerrit topic by appending it after a slash character.

Git SSH Commands

If you find you are frequently executing Gerrit commands via SSH, you may wish to add something like the following to your ~/.ssh/config file:

Host review
  Hostname review.openstack.org
  Port 29418

Which may shorten some SSH commands; the following are equivalent:

ssh -p 29418 review.openstack.org gerrit ls-projects
ssh review gerrit ls-projects

Reviewing a Change

Log in to https://review.openstack.org/ to see proposed changes, and review them.

To provide a review for a proposed change in the Gerrit UI, click on the Review button (it will be next to the buttons that will provide unified or side-by-side diffs in the browser). In the code review, you can add a message, as well as a vote (+1,0,-1).

Any Openstack developer may propose or comment on a change (including voting +1/0/-1 on it). Openstack projects have a policy requiring two positive reviews from core reviewers. A vote of +2 is allowed from core reviewers, and should be used to indicate that they are a core reviewer and are leaving a vote that should be counted as such.

When a review has two +2 reviews and one of the core team believes it is ready to be merged, he or she should leave a +1 vote in the "Approved" category. You may do so by clicking the "Review" button again, with or without changing your code review vote and optionally leaving a comment. When a +1 Approved review is received, Jenkins will run tests on the change, and if they pass, it will be merged.

Gerrit Best Practices

If you are working on unrelated changes, you should use a topic branch so that there isn't a dependency between the changes.

When you start working on a new change, make sure you have the current repository head from GitHub.

For more information about uploading changes to gerrit, see the Uploading Changes section of the Gerrit manual.

Gerrit Errors

missing Change-Id in commit message

If you see an error like this:

 ! [remote rejected] HEAD -> refs/for/master (missing Change-Id in commit message)

Make sure that you have the Change-Id hook installed. If you don't, install it now, and the run git commit --amend and re-save your commit message. The hook will then add a Change-Id line.

If you did have the hook installed, there may be a syntax error with the Change-Id line. It must be in the last paragraph of the commit message, and it must be at the beginning of the line. Your commit message should look like this in your editor:

The text of your commit message is here.

Change-Id: I5f55e68d1bdb42a0fa6f0b1a5432786d0395da51

squash commits first

If you see this message:

 ! [remote rejected] HEAD -> refs/for/master (squash commits first)

It means that you are trying to update an existing change in Gerrit, but you created two separate commits. Normally to update a change you should amend an existing commit (see Updating a Change). If you have already made a second commit, you will need squash the last two commits in your tree. To do that, run:

git rebase -i HEAD~2

Your editor should appear with two commits listed, one per line. Change the word "pick" on the second line to "squash", so that it looks like:

pick 1458567 Fix bug 1014727
pick 7284e97 Document underlying technologies
pick fac4698 Clean up on section
pick xxxxxxx 2nd commit back
squash yyyyyyy head

And save. You should then be able to upload your commit with git review.

can not create new references

If you try to send a draft with git review -D and it fails like this:

 ! [remote rejected] HEAD -> refs/draft/master (can not create new references) 

Then check that you are running git-review version 1.16 or later. You can install the lastest version with pip:

pip install git-review

Gerrit Merge Problems

Gerrit will fast-forward or merge changes as necessary when they are approved. If a conflict would be created by a merge, gerrit will not merge the change and will record an error message in the comments for the change. In these cases, you may need to rebase or merge the change, or if the repository head has changed significantly, you may need to change the patch.

If you don't already have the patch in your local repository, Gerrit provides commands on the web page for each change indicating how to download that change. You can then use git to correct the problem.

If you encounter other error messages from Gerrit, the Error Messages section of the Gerrit manual may offer some tips.

Test Failures

When a new patchset is uploaded to Gerrit, that project's "check" tests are run on the patchset by Jenkins. Once completed the test results are reported to Gerrit by Jenkins in the form of a Verified: +/-1 vote. After code reviews have been completed and a change receives an Approved: +1 vote that project's "gate" tests are run on the change by Jenkins. Jenkins reports the results of these tests back to Gerrit in the form of a Verified: +/-2 vote. Code merging will only occur after the gate tests have passed successfully and received a Verified: +2. You can view the state of tests currently being run on the Zuul Status and Jenkins Dashboard pages.

If a change fails tests in Jenkins, please follow the steps below:

  1. Jenkins leaves a comment in the review with links to the log files for the test run. Follow those links and examine the output from the test. It will include a console log, and in the case of unit tests, HTML output from the test runner, or in the case of a devstack-gate test, it may contain quite a large number of system logs.
  2. Examine the console log or other relevant log files to determine the cause of the error. If it is related to your change, you should fix the problem and upload a new patchset.
  3. If the problem is due to non-deterministic behavior already merged, and is unrelated to your change, you should do the following to help other developers who may be affected by the same issue, and to focus attention of QA, CI, and other developers working to fix high-impact bugs and improve test systems:
  4. Visit http://status.openstack.org/rechecks/ to see if one of the bugs listed there matches the error you've seen. If your error isn't there, then:
    • Identify which project(s) are affected, and search for a related bug on Launchpad. If you do not find an existing bug, file a new one (and be sure to include the error message). If the problem is due to an infrastructure problem (such as Jenkins, Gerrit, etc.), file (or search for) the bug against the "openstack-ci" project.
  5. Once you have a bug number in hand:
    • To re-run the check jobs (before a change has been approved), leave a comment with the form "recheck bug ####".
    • To re-run the gate jobs (after a change has been approved), leave a comment with the form "reverify bug ####".
  6. This will update the rechecks status page and help others quickly identify the issue if it occurs again.

If you need to re-run tests and it does not make sense to include a bug number (perhaps there is no error, you've just made a draft change visible and want it tested or you're updating test results because you know that a related branch has changed since the last time they were run), you may leave a comment with the form "recheck no bug" (or "reverify no bug"). Please only do this if you are certain there is no bug that needs to be addressed.

Test failures due to changes in the code

There might be some cases in which the submitted patch changes the way a tempest test behaves. In this case, the tempest test needs to be modified, so that it tests the new behaviour instead of the old one. The route for this is propose the tempest change, and get core contributors from the core project to +1 it, saying that they agree with the change. Once the tempest change has been accepted and merged, the original change could be tested again.

Merge Commits

When a branch is pushed to gerrit (either manually, or via git-review), each commit in the branch that is not in Gerrit's copy of the tree is turned into a new change for review (unless that commit has a Change-Id that corresponds to an existing change, in which case, the change is updated). This means that if a developer merges a branch from another source into their local repository and pushes to Gerrit, hundreds of new changes may be created. This is almost certainly not what was intended. For that reason, Gerrit is configured not to accept merge commits in the general case.

Caution: The following describes an experimental process and is not generally applicable yet:

However, merge commits are very useful for feature branches -- development branches that fork from the main line of development, occasionally receiving updates from the main line, and when development is complete, merging back into the main line. For these purposes, members of the $PROJECT-milestone group are permitted to upload merge commits to Gerrit. These users must take special care when dealing with merge commits to avoid the problems mentioned above. The following tips will help avoid problems with merge commits:

  • Don't merge branches from gerrit and outside of gerrit (eg, GitHub or personal branches).
  • When developing, follow the branching model described in GerritWorkflow, this will avoid creating merge commits locally.
  • Use git-review to upload your changes to Gerrit. By default, if git-review would create or update more than one commit, it will list the commits and ask you if that is what you intend to do. Pay attention to that, and if you see that too many commits are being uploaded, say "no" and clean up your local branch.
  • To merge master into a feature branch, do the following:
git checkout feature-branch
git pull --ff-only origin feature-branch
git checkout -b merge-branch
git merge origin/master
# Amend the merge commit to automatically add a Change-ID to the commit message:
GIT_EDITOR=/bin/true git commit --amend
git review -R feature-branch
git checkout master
git branch -D merge-branch

Note that follows the same model described in GerritWorkflow of using a topic branch for each independent unit of local development. In this case, the "merge-branch" branch is being used to generate the merge commit, and once submitted, is no longer needed and can be (optionally) removed. You may continue to use your local copy of the feature-branch as normal, pulling fast-forward only commits from Gerrit. The following similar process may be used to merge the feature branch into master, terminating development on that branch:

git checkout master
git pull --ff-only origin master
git checkout -b merge-branch
git merge origin/feature-branch
# Amend the merge commit to automatically add a Change-ID to the commit message:
GIT_EDITOR=/bin/true git commit --amend
git review -R
git checkout master
git branch -D merge-branch

Release Management


Between the Milestone Branch Point and the release of the corresponding milestone, there needs to be a separate branch in Gerrit for changes destined for the milestone release. Meanwhile, development on the master branch should continue as normal (with the addition that changes proposed for the milestone should also be proposed for master, and some changes for master may need to be applied to milestone-proposed).

This process creates an ephemeral milestone-proposed branch that is only available in Gerrit during the milestone process. When the milestone is released, a tag is applied to the final commit to record the state of the branch at the time.

Create milestone-proposed Branch

This step should be performed by the OpenStack Release Manager at the Release Branch Point.

  • Go to https://review.openstack.org/ and sign in
  • Select Admin, Projects, then the project
  • Select Branches
  • Enter milestone-proposed in the Branch Name field, and HEAD as the Initial Revision, then press Create Branch

In your local checkout:

git checkout master
git pull
git checkout milestone-proposed

Authoring Changes for milestone-proposed

Create topic branches as normal, but branch them from milestone-proposed rather than master.

git checkout milestone-proposed
git pull
git checkout -b MY-TOPIC-BRANCH

Changes for milestone-proposed should be submitted with:

git push gerrit HEAD:refs/for/milestone-proposed

Submit Changes in master to milestone-proposed

If a change to master should also be included in milestone-proposed, use this procedure to cherry-pick that change and submit it for review.

git checkout milestone-proposed
git pull
git checkout -b master-to-mp
git cherry-pick -x <SHA1 or "master">
git push gerrit HEAD:refs/for/milestone-proposed
git branch -D master-to-mp

git cherry-pick master will pick the most recent commit from master to apply, if you want a different patch, use the SHA1 of the commit instead.

The '-x' flag will ensure the commit message records the SHA1 hash of the original commit in master.

If there are conflicts when cherry-picking, do not delete the 'Conflicts' lines GIT adds to the commit message. These are valuable to reviewers to identify files which need extra attention.

Submitting Changes in milestone-proposed to master

Changes that originate in milestone-proposed should also be submitted to master. Use these commands to make an up-to-date topic branch from master, then cherry-pick changes from milestone-proposed to be applied to master.

git checkout master
git pull
git checkout -b mp-to-master
git cherry-pick <SHA1 or milestone-proposed>
git review
git branch -D mp-to-master

git cherry-pick milestone-proposed will pick the most recent commit from milestone-proposed to apply, if you want a different patch, use the SHA1 of the commit instead.

Tagging a Release

This step should be performed by the OpenStack Release Manager when the release is made.

To tag the tip of the milestone-proposed branch with a release tag and push that tag to gerrit and GitHub, run the following commands:

git checkout milestone-proposed
git pull
git push gerrit RELEASE-TAG-NAME

Running `git tag -s` signs the tag using GPG, so it's important to ensure that the person making the release have a valid GPG key.

Make sure you're only adding a single tag when pushing to gerrit.

End of Milestone

This step should be performed by the OpenStack Release Manager after the release is tagged.

When the milestone process is complete and the released commit is tagged, remove the milestone-proposed branch. The tag will persist, even after the branch is deleted, making it possible to restore the state of the tree.

  • Go to https://review.openstack.org/ and sign in
  • Select Admin, Projects, then the project
  • Select Branches
  • Select the checkbox next to milestone-proposed and hit Delete


See the Gerrit documentation, especially the User Guide, for more information on how to use Gerrit. It is also available within Gerrit by clicking on the Documentation link on the top of the page.

The Mahara Project also uses Git, Gerrit, and Jenkins in a similar manner (though with Gitorious instead of GitHub).

A description of many of the elements of the git workflow