Queue

Projects that interact with each other should share a queue. This is especially used in a dependent pipeline. The project.queue can optionally refer to a specific queue object that can further configure the behavior of the queue.

Here is an example queue configuration.

- queue:
    name: integrated
    per-branch: false

queue

The attributes available on a queue are as follows (all are optional unless otherwise specified):

queue.name (required)

This is used later in the project definition to refer to this queue.

queue.per-branch
Default: false

Queues by default define a single queue for all projects and branches that use it. This is especially important if projects want to do upgrade tests between different branches in the gate. If a set of projects doesn’t have this use case it can configure the queue to create a shared queue per branch for all projects. This can be useful for large projects to improve the throughput of a gate pipeline as this results in shorter queues and thus less impact when a job fails in the gate. Note that this means that all projects that should be gated must have aligned branch names when using per branch queues. Otherwise changes that belong together end up in different queues.

queue.allow-circular-dependencies
Default: false

Define if Zuul is allowed to process circular dependencies between changes for this queue. All projects that are part of a dependency cycle must share the same change queue.

In case Zuul detects a dependency cycle it will make sure that every change also includes all other changes that are part of the cycle. However each change will still be a normal item in the queue with its own jobs.

Reporting of success will be postponed until all items in the cycle succeeded. In case of a failure in any of those items the whole cycle will be dequeued.

An error message will be posted to all items of the cycle in case some items fail to report (e.g. merge failure when some items were already merged). In this case the target branch(es) might be in a broken state.

In general, circular dependencies are considered to be an antipattern since they add extra constraints to continuous deployment systems. Additionally, due to the lack of atomicity in merge operations in code review systems, it may be possible for only part of a cycle to be merged. In that case, manual interventions (such as reverting a commit, or bypassing gating to force-merge the remaining commits) may be required.

Warning

If the remote system is able to merge the first but unable to merge the second or later change in a dependency cycle, then the gating system for a project may be broken and may require an intervention to correct.