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Convert taskcluster/docs/*.rst (including transforms, kinds, optimization, howto subdirectories) and gecko_taskgraph test docs to MyST-flavored Markdown. Refresh allowed-warnings glob for release-promotion-action from .rst to .md. Differential Revision: https://phabricator.services.mozilla.com/D304225
133 lines
5.3 KiB
Markdown
133 lines
5.3 KiB
Markdown
# Taskgraph Overview
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Taskgraph builds a directed acyclic graph, where each node in the graph
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represents a task, and each edge represents the dependency relationships
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between them.
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See Taskgraph's [graph generation documentation] for more details.
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## Decision Task
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The decision task is the first task created when a new graph begins. It is
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responsible for creating the rest of the task graph.
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The decision task for pushes is defined in-tree, in `.taskcluster.yml`. That
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task description invokes `mach taskcluster decision` with some metadata about
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the push. That mach command determines the required graph of tasks to submit,
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then calls the Taskcluster API to create the tasks.
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:::{note}
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`mach taskgraph decision` is *not* meant to be invoked by humans.
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Instead, follow [this guide] (prepending `mach` to all commands) to
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invoke Taskgraph locally without submitting anything to Taskcluster.
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:::
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(kinds)=
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## Kinds
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Generation starts with "kinds". These are yaml files that denote groupings of
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tasks that are loosely related to one another. For example, in Gecko there are
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`build` and `test` kinds. Each kind has its own directory under
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{searchfox}`taskcluster/kinds` which contains a `kind.yml` file.
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For more information on kinds, see Taskgraph's [kind documentation]. For a
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list of available kinds in `mozilla-central`, see the {doc}`kinds reference
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</taskcluster/kinds>`.
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## Loader
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Next, a "loader" is responsible for parsing each `kind.yml` file and turning
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it into an initial set of tasks. Loaders will always parse kinds in an ordering
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satisfying the `kind-dependencies` key.
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See Taskgraph's [loader documentation] for more details.
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(transforms)=
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## Transforms
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After the initial set of tasks are loaded, transformations are applied to each
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task. Transforms are Python functions that take a generator of tasks as input,
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and yields a generator of tasks as output. Possibly modifying, adding or removing
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tasks along the way.
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See Taskgrpah's [transforms documentation] for more details on transforms, or
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the {doc}`transforms section </taskcluster/transforms/index>` for information
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on some of the transforms available in `mozilla-central`.
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## Target Tasks
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After transformation is finished, the [target_tasks] module filters out any
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tasks that aren't applicable to the current {doc}`parameter set
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</taskcluster/parameters>`.
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## Optimization
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After the "target graph" is generated, an optimization process looks to remove
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or replace unnecessary tasks in the graph. For instance, a task may be removed
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if the push doesn't modify any of the files that could affect it.
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See Taskgraph's [optimization documentation] for more details, or the
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{doc}`optimization strategies <optimization/index>` available in
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`mozilla-central`.
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## Task Parameterization
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A few components of tasks are only known at the very end of the decision task
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-- just before the `queue.createTask` call is made. These are specified
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using simple parameterized values, as follows:
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`{"relative-datestamp": "certain number of seconds/hours/days/years"}`
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: Objects of this form will be replaced with an offset from the current time
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just before the `queue.createTask` call is made. For example, an
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artifact expiration might be specified as `{"relative-datestamp": "1
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year"}`.
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`{"task-reference": "string containing <dep-name>"}`
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: The task definition may contain "task references" of this form. These will
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be replaced during the optimization step, with the appropriate taskId for
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the named dependency substituted for `<dep-name>` in the string.
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Additionally, `decision` and `self` can be used a dependency names to refer
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to the decision task, and the task itself. Multiple labels may be
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substituted in a single string, and `<<>` can be used to escape a literal
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`<`.
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`{"artifact-reference": "..<dep-name/artifact/name>.."}`
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: Similar to a `task-reference`, but this substitutes a URL to the queue's
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`getLatestArtifact` API method (for which a GET will redirect to the
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artifact itself).
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(taskgraph-graph-config)=
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## Graph Configuration
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There are several configuration settings that are pertain to the entire
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taskgraph. These are specified in {file}`config.yml` at the root of the
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taskgraph configuration (typically {file}`taskcluster`). The available
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settings are documented inline in {searchfox}`taskcluster/gecko_taskgraph/config.py`.
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(taskgraph-trust-domain)=
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## Action Tasks
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Action Tasks are tasks which perform an action based on a manual trigger (e.g
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clicking a button in Treeherder). Actions are how it is possible to retrigger
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or "Add New Jobs".
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For more information, see Taskgraph's [actions documentation].
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(target-tasks-1)=
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[actions documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/howto/create-actions.html
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[graph generation documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/task-graphs.html
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[kind documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/kind.html
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[loader documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/loading.html
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[optimization documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/optimization.html
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[target_tasks]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/optimization.html
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[this guide]: https://taskcluster-taskgraph.readthedocs.io/en/latest/howto/run-locally.html
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[transforms documentation]: https://taskcluster-taskgraph.readthedocs.io/en/latest/concepts/transforms.html
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