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title: Launchers

Launchers

Zuul has a modular architecture for launching jobs. Currently, the only supported module interfaces with Gearman. This design allows any system to run jobs for Zuul simply by interfacing with a Gearman server. The recommended way of integrating a new job-runner with Zuul is via this method.

If Gearman is unsuitable, Zuul may be extended with a new launcher module. Zuul makes very few assumptions about the interface to a launcher -- if it can trigger jobs, cancel them, and receive success or failure reports, it should be able to be used with Zuul. Patches to this effect are welcome.

Gearman

Gearman is a general-purpose protocol for distributing jobs to any number of workers. Zuul works with Gearman by sending specific information with job requests to Gearman, and expects certain information to be returned on completion. This protocol is described in Zuul-Gearman Protocol.

The Gearman Jenkins Plugin makes it easy to use Jenkins with Zuul by providing an interface between Jenkins and Gearman. In this configuration, Zuul asks Gearman to run jobs, and Gearman can then distribute those jobs to any number of Jenkins systems (including multiple Jenkins masters).

In order for Zuul to run any jobs, you will need a running Gearman server. Zuul includes a Gearman server, and it is recommended that it be used as it supports the following features needed by Zuul:

Canceling jobs in the queue (admin protocol command "cancel job").
Strict FIFO queue operation (gearmand's round-robin mode may be sufficient, but is untested).

To enable the built-in server, see the gearman_server section of zuul.conf. Be sure that the host allows connections from Zuul and any workers (e.g., Jenkins masters) on TCP port 4730, and nowhere else (as the Gearman protocol does not include any provision for authentication).

Gearman Jenkins Plugin

The Gearman Plugin can be installed in Jenkins in order to facilitate Jenkins running jobs for Zuul. Install the plugin and configure it with the hostname or IP address of your Gearman server and the port on which it is listening (4730 by default). It will automatically register all known Jenkins jobs as functions that Zuul can invoke via Gearman.

Any number of masters can be configured in this way, and Gearman will distribute jobs to all of them as appropriate.

No special Jenkins job configuration is needed to support triggering by Zuul.

Zuul Parameters

Zuul will pass some parameters with every job it launches. The Gearman Plugin will ensure these are supplied as Jenkins build parameters, so they will be available for use in the job configuration as well as to the running job as environment variables. They are as follows:

ZUUL_UUID: Zuul provided key to link builds with Gerrit events
ZUUL_REF: Zuul provided ref that includes commit(s) to build
ZUUL_COMMIT: The commit SHA1 at the head of ZUUL_REF
ZUUL_PROJECT: The project that triggered this build
ZUUL_PIPELINE: The Zuul pipeline that is building this job
ZUUL_URL: The url for the zuul server as configured in zuul.conf. A test runner may use this URL as the basis for fetching git commits.

The following additional parameters will only be provided for builds associated with changes (i.e., in response to patchset-created or comment-added events):

ZUUL_BRANCH: The target branch for the change that triggered this build
ZUUL_CHANGE: The Gerrit change ID for the change that triggered this build
ZUUL_CHANGE_IDS: All of the Gerrit change IDs that are included in this build (useful when the DependentPipelineManager combines changes for testing)
ZUUL_PATCHSET: The Gerrit patchset number for the change that triggered this build

The following additional parameters will only be provided for post-merge (ref-updated) builds:

ZUUL_OLDREV: The SHA1 of the old revision at this ref (recall the ref name is in ZUUL_REF)
ZUUL_NEWREV: The SHA1 of the new revision at this ref (recall the ref name is in ZUUL_REF)
ZUUL_SHORT_OLDREV: The shortened (7 character) SHA1 of the old revision
ZUUL_SHORT_NEWREV: The shortened (7 character) SHA1 of the new revision

In order to test the correct build, configure the Jenkins Git SCM plugin as follows:

Source Code Management:
  Git
    Repositories:
      Repository URL:  <your Gerrit or Zuul repository URL>
        Advanced:
          Refspec: ${ZUUL_REF}
    Branches to build:
      Branch Specifier: ${ZUUL_COMMIT}
          Advanced:
          Clean after checkout: True

That should be sufficient for a job that only builds a single project. If you have multiple interrelated projects (i.e., they share a Zuul Change Queue) that are built together, you may be able to configure the Git plugin to prepare them, or you may chose to use a shell script instead. As an example, the OpenStack project uses the following script to prepare the workspace for its integration testing:

https://github.com/openstack-infra/devstack-gate/blob/master/devstack-vm-gate-wrap.sh

Zuul-Gearman Protocol

This section is only relevant if you intend to implement a new kind of worker that runs jobs for Zuul via Gearman. If you just want to use Jenkins, see Gearman Jenkins Plugin instead.

The Zuul protocol as used with Gearman is as follows:

Starting Builds

To start a build, Zuul invokes a Gearman function with the following format:

build:FUNCTION_NAME

where FUNCTION_NAME is the name of the job that should be run. If the job should run on a specific node (or class of node), Zuul will instead invoke:

build:FUNCTION_NAME:NODE_NAME

where NODE_NAME is the name or class of node on which the job should be run. This can be specified by setting the ZUUL_NODE parameter in a parameter-function (see includes section in zuulconf).

Zuul sends the ZUUL* parameters described in Zuul Parameters encoded in JSON format as the argument included with the SUBMIT_JOB_UNIQ request to Gearman. A unique ID (equal to the ZUUL_UUID parameter) is also supplied to Gearman, and is accessible as an added Gearman parameter with GRAB_JOB_UNIQ.

When a Gearman worker starts running a job for Zuul, it should immediately send a WORK_DATA packet with the following information encoded in JSON format:

name: The name of the job.
number: The build number (unique to this job).
manager: A unique identifier associated with the Gearman worker that can abort this build. See Stopping Builds for more information.
url (optional): The URL with the status or results of the build. Will be used in the status page and the final report.

It should then immediately send a WORK_STATUS packet with a value of 0 percent complete. It may then optionally send subsequent WORK_STATUS packets with updated completion values.

When the build is complete, it should send a final WORK_DATA packet with the following in JSON format:

result: Either the string 'SUCCESS' if the job succeeded, or any other value that describes the result if the job failed.

Finally, it should send either a WORK_FAIL or WORK_COMPLETE packet as appropriate. A WORK_EXCEPTION packet will be interpreted as a WORK_FAIL, but the exception will be logged in Zuul's error log.

Stopping Builds

If Zuul needs to abort a build already in progress, it will invoke the following function through Gearman:

stop:MANAGER_NAME

Where MANAGER_NAME is the name of the manager worker supplied in the initial WORK_DATA packet when the job started. This is used to direct the stop: function invocation to the correct Gearman worker that is capable of stopping that particular job. The argument to the function should be the following encoded in JSON format:

name: The job name of the build to stop.
number: The build number of the build to stop.

The original job is expected to complete with a WORK_DATA and WORK_FAIL packet as described in Starting Builds.

Build Descriptions

In order to update the job running system with a description of the current state of all related builds, the job runner may optionally implement the following Gearman function:

set_description:MANAGER_NAME

Where MANAGER_NAME is used as described in Stopping Builds. The argument to the function is the following encoded in JSON format:

name: The job name of the build to describe.
number: The build number of the build to describe.
html_description: The description of the build in HTML format.

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