:title: Launchers

.. _Gearman: http://gearman.org/

.. _`Gearman Plugin`:
   https://wiki.jenkins-ci.org/display/JENKINS/Gearman+Plugin

.. _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

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 paremeter-function (see :ref:`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.