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diff --git a/taskcluster/docs/taskgraph.rst b/taskcluster/docs/taskgraph.rst new file mode 100644 index 0000000000..5b3ac83643 --- /dev/null +++ b/taskcluster/docs/taskgraph.rst @@ -0,0 +1,140 @@ +Taskgraph Overview +================== + +Taskgraph builds a directed acyclic graph, where each node in the graph +represents a task, and each edge represents the dependency relationships +between them. + +See Taskgraph's `graph generation documentation`_ for more details. + +Decision Task +------------- + +The decision task is the first task created when a new graph begins. It is +responsible for creating the rest of the task graph. + +The decision task for pushes is defined in-tree, in ``.taskcluster.yml``. That +task description invokes ``mach taskcluster decision`` with some metadata about +the push. That mach command determines the required graph of tasks to submit, +then calls the Taskcluster API to create the tasks. + +.. note:: + + ``mach taskgraph decision`` is *not* meant to be invoked by humans. + Instead, follow `this guide`_ (prepending ``mach`` to all commands) to + invoke Taskgraph locally without submitting anything to Taskcluster. + +.. _kinds: + +Kinds +----- + +Generation starts with "kinds". These are yaml files that denote groupings of +tasks that are loosely related to one another. For example, in Gecko there are +``build`` and ``test`` kinds. Each kind has its own directory under +`taskcluster/ci`_ which contains a ``kind.yml`` file. + +For more information on kinds, see Taskgraph's `kind documentation`_. For a +list of available kinds in ``mozilla-central``, see the :doc:`kinds reference +</taskcluster/kinds>`. + +Loader +------ + +Next, a "loader" is responsible for parsing each ``kind.yml`` file and turning +it into an initial set of tasks. Loaders will always parse kinds in an ordering +satisfying the ``kind-dependencies`` key. + +See Taskgraph's `loader documentation`_ for more details. + +.. _transforms: + +Transforms +---------- + +After the initial set of tasks are loaded, transformations are applied to each +task. Transforms are Python functions that take a generator of tasks as input, +and yields a generator of tasks as output. Possibly modifying, adding or removing +tasks along the way. + +See Taskgrpah's `transforms documentation`_ for more details on transforms, or +the :doc:`transforms section </taskcluster/transforms/index>` for information +on some of the transforms available in ``mozilla-central``. + +Target Tasks +------------ + +After transformation is finished, the `target_tasks`_ module filters out any +tasks that aren't applicable to the current :doc:`parameter set +</taskcluster/parameters>`. + +Optimization +------------ + +After the "target graph" is generated, an optimization process looks to remove +or replace unnecessary tasks in the graph. For instance, a task may be removed +if the push doesn't modify any of the files that could affect it. + +See Taskgraph's `optimization documentation`_ for more details, or the +:doc:`optimization strategies <optimization/index>` available in +``mozilla-central``. + + +Task Parameterization +--------------------- + +A few components of tasks are only known at the very end of the decision task +-- just before the ``queue.createTask`` call is made. These are specified +using simple parameterized values, as follows: + +``{"relative-datestamp": "certain number of seconds/hours/days/years"}`` + Objects of this form will be replaced with an offset from the current time + just before the ``queue.createTask`` call is made. For example, an + artifact expiration might be specified as ``{"relative-datestamp": "1 + year"}``. + +``{"task-reference": "string containing <dep-name>"}`` + The task definition may contain "task references" of this form. These will + be replaced during the optimization step, with the appropriate taskId for + the named dependency substituted for ``<dep-name>`` in the string. + Additionally, `decision` and `self` can be used a dependency names to refer + to the decision task, and the task itself. Multiple labels may be + substituted in a single string, and ``<<>`` can be used to escape a literal + ``<``. + +``{"artifact-reference": "..<dep-name/artifact/name>.."}`` + Similar to a ``task-reference``, but this substitutes a URL to the queue's + ``getLatestArtifact`` API method (for which a GET will redirect to the + artifact itself). + +.. _taskgraph-graph-config: + +Graph Configuration +------------------- + +There are several configuration settings that are pertain to the entire +taskgraph. These are specified in :file:`config.yml` at the root of the +taskgraph configuration (typically :file:`taskcluster/ci/`). The available +settings are documented inline in `taskcluster/gecko_taskgraph/config.py +<https://searchfox.org/mozilla-central/source/taskcluster/gecko_taskgraph/config.py>`_. + +.. _taskgraph-trust-domain: + +Action Tasks +------------ + +Action Tasks are tasks which perform an action based on a manual trigger (e.g +clicking a button in Treeherder). Actions are how it is possible to retrigger +or "Add New Jobs". + +For more information, see Taskgraph's `actions documentation`_. + +.. _graph generation documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/task-graphs.html +.. _this guide: https://taskcluster-taskgraph.readthedocs.io/en/latest/howto/run-locally.html +.. _taskcluster/ci: https://searchfox.org/mozilla-central/source/taskcluster/ci +.. _kind documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/kind.html +.. _loader documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/loading.html +.. _transforms documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/transforms.html +.. _target_tasks: +.. _optimization documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/optimization.html +.. _actions documentation: https://taskcluster-taskgraph.readthedocs.io/en/latest/howto/create-actions.html |