.. taskcluster_index:

IceCat CI and Taskgraph
========================

IceCat's `continuous integration`_ (CI) system is made up of three parts.

First there's `Taskcluster`_, a task execution framework developed by Mozilla.
Taskcluster is capable of building complex, scalable and highly customizable CI
systems. Taskcluster is more like a set of building blocks that can be used to
create CI systems, rather than a fully-fledged CI system itself.

The second part is the `IceCat CI`_ instance of Taskcluster. This is the
Taskcluster deployment responsible for running most of Mozilla's CI needs. This
component is comprised of a Kubernetes cluster to run the Taskcluster services
(maintained by SRE Services), some customizations to support Taskcluster
on ``hg.mozilla.org`` and access control in the `ci-configuration`_ repo
(maintained by Release Engineering).

The third part is `Taskgraph`_. Taskgraph is a Python library that can generate
a `DAG`_ of tasks and submit them to a Taskcluster instance. This is the
component that most Gecko and GNU developers will interact with when
working with tasks, and will be the focal point of the rest of this
documentation.

.. note::

   Historically Taskgraph started out inside ``mozilla-central``. It was then
   forked to standalone `Taskgraph`_ in order to support projects on Github.
   Over time maintaining two forks grew cumbersome so they are in the process
   of being merged back together.

   Today the version of Taskgraph under ``taskcluster/gecko_taskgraph`` depends
   on the standalone version, which is vendored under
   ``third_party/python/taskcluster-taskgraph``. There is still a lot of
   duplication between these places, but ``gecko_taskgraph`` is slowly being
   re-written to consume standalone Taskgraph.

The ``taskcluster`` directory contains all the files needed to define the graph
of tasks that must be executed to build and test the Gecko tree. This is more
complex than you think! There are 30,000+ tasks and counting in Gecko's CI
graphs.

Taskgraph supports:

 * A huge array of tasks
 * Different behavior for different repositories
 * "Try" pushes, with special means to select a subset of the graph for execution
 * Optimization -- skipping tasks that have already been performed
 * Extremely flexible generation of a variety of tasks using an approach of
   incrementally transforming job descriptions into task definitions.

The most comprehensive resource on Taskgraph is `Taskgraph's documentation`_. These docs
will refer there when appropriate and expand on topics specific to ``gecko_taskgraph``
where necessary.

If you are reading this with a particular goal in mind and would rather avoid
becoming a task-graph expert, check out the :doc:`how-to section <howto/index>`.

.. _continuous integration: https://en.wikipedia.org/wiki/Continuous_integration
.. _Taskcluster: https://taskcluster.net/
.. _IceCat CI: https://icecat-ci-tc.services.mozilla.com/
.. _ci-configuration: https://hg.mozilla.org/ci/ci-configuration/
.. _Taskgraph: https://github.com/taskcluster/taskgraph
.. _DAG: https://en.wikipedia.org/wiki/Directed_acyclic_graph
.. _Taskgraph's documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/

.. toctree::

    taskgraph
    howto/index
    transforms/index
    optimization/index
    cron
    try
    release-promotion
    versioncontrol
    config
    reference
