Github Checks API

Github provides two distinct methods for reporting results; a “checks” and a “status” API.

The checks API provides some additional features compared to the status API like file comments and custom actions (e.g. cancel a running build).

Either can be chosen when configuring Zuul to report for your Github project. However, there are some considerations to take into account when choosing the API.

Design decisions

The Github checks API defines the concepts of Check Suites and Check Runs. Check suites are a collection of check runs for a specific commit and summarize a final status

A priori the check suite appears to be a good mapping for a pipeline execution in Zuul, where a check run maps to a single job execution that is part of the pipeline run. Unfortunately, there are a few problematic restrictions mapping between Github and Zuul concepts.

Github check suites are opaque and the current status, duration and the overall conclusion are all calculated and set automatically whenever an included check run is updated. Most importantly, there can only be one check suite per commit SHA, per app. Thus there is no facility for for Zuul to create multiple check suite results for a change, e.g. one check suite for each pipeline such as check and gate.

The Github check suite thus does not map well to Zuul’s concept of multiple pipelines for a single change. Since a check suite is unique and global for the change, it can not be used to flag the status of arbitrary pipelines. This makes the check suite API insufficient for recording details that Zuul needs such as “the check pipeline has passed but the gate pipeline has failed”.

Another issue is that Zuul only reports on the results of the whole pipeline, not individual jobs. Reporting each Zuul job as a separate check is problematic for a number of reasons.

Zuul often runs the same job for the same change multiple times; for example in the check and gate pipeline. There is no facility for these runs to be reported differently in the single check suite for the Github change.

When configuring branch protection in Github, only a check run can be selected as required status check. This is in conflict with managing jobs in pipelines with Zuul. For example, to implement branch protection on GitHub would mean listing each job as a dedicated check, leading to a check run list that is not kept in sync with the project’s Zuul pipeline configuration. Additionally, you lose some of Zuul’s features like non-voting jobs as Github branch protections has no concept of a non-voting job.

Thus Zuul can integrate with the checks API, but only at a pipeline level. Each pipeline execution will map to a check-run result reported to Github.

Behaviour in Zuul


The Github reporter is able to report both a status pipeline.<reporter>.<github source>.status or a check pipeline.<reporter>.<github source>.check. While it’s possible to configure a Github reporter to report both, it’s recommended to use only one. Reporting both might result in duplicated status check entries in the Github PR (the section below the comments).


The Github driver is able to trigger on a reported check (check_run) similar to a reported status (status).


While trigger and reporter differentiates between status and check, the Github driver does not differentiate between them when it comes to pipeline requirements. This is mainly because Github also doesn’t differentiate between both in terms of branch protection and status checks.

Actions / Events

Github provides a set of default actions for check suites and check runs. Those actions are available as buttons in the Github UI. Clicking on those buttons will emit webhook events which will be handled by Zuul.

These actions are only available on failed check runs / check suites. So far, a running or successful check suite / check run does not provide any action from Github side.

Available actions are:

Re-run all checks

Github emits a webhook event with type check_suite and action rerequested that is meant to re-run all check-runs contained in this check suite. Github does not provide the list of check-runs in that case, so it’s up to the Github app what should run.

Re-run failed checks

Github emits a webhook event with type check_run and action rerequested for each failed check run contained in this suite.


Github emits a webhook event with type check_run and action rerequested for the specific check run.

Zuul will handle all events except for the Re-run all checks event; it does not make sense in the Zuul model to trigger all pipelines to run simultaneously.

These events are unable to be customized in Github. Github will always report “You have successfully requested …” despite nothing listening to the event. Therefore, it might be a solution to handle the Re-run all checks event in Zuul similar to Re-run failed checks just to not do anything while Github makes the user believe an action was really triggered.

File comments (annotations)

Check runs can be used to post file comments directly in the files of the PR. Those are similar to user comments, but must provide some more information.

Zuul jobs can already return file comments via zuul_return (see: Return Values). We can simply use this return value, build the necessary annotations (how Github calls it) from it and attach them to the check run.

Custom actions

Check runs can provide some custom actions which will result in additional buttons being available in the Github UI for this specific check run. Clicking on such a button will emit a webhook event with type check_run and action requested_action and will additionally contain the id/name of the requested action which we can define when creating the action on the check run.

We could use these custom actions to provide some “Re-run” action on a running check run (which might otherwise be stuck in case a check run update fails) or to abort a check run directly from the Github UI.

Restrictions and Recommendations

Although both the checks API and the status API can be activated for a Github reporter at the same time, it’s not recommended to do so as this might result in multiple status checks to be reported to the PR for the same pipeline execution (which would result in duplicated entries in the status section below the comments of a PR).

In case the update on a check run fails (e.g. request timeout when reporting success or failure to Github), the check run will stay in status “in_progess” and there will be no way to re-run the check run via the Github UI as the predefined actions are only available on failed check runs. Thus, it’s recommended to configure a comment trigger on the pipeline to still be able to trigger re-run of the stuck check run via e.g. “recheck”.

The check suite will only list check runs that were reported by Zuul. If the requirements for a certain pipeline are not met and it is not run, the check run for this pipeline won’t be listed in the check suite. However, this does not affect the required status checks. If the check run is enabled as required, Github will still show it in the list of required status checks - even if it didn’t run yet - just not in the check suite.