221 lines
8.9 KiB
ReStructuredText
221 lines
8.9 KiB
ReStructuredText
How Tos
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=======
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All of this equipment is here to help you get your work done more efficiently.
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However, learning how task-graphs are generated is probably not the work you
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are interested in doing. This section should help you accomplish some of the
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more common changes to the task graph with minimal fuss.
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.. important::
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If you cannot accomplish what you need with the information provided here,
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please consider whether you can achieve your goal in a different way.
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Perhaps something simpler would cost a bit more in compute time, but save
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the much more expensive resource of developers' mental bandwidth.
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Task-graph generation is already complex enough!
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If you want to proceed, you may need to delve into the implementation of
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task-graph generation. The documentation and code are designed to help, as
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are the authors - ``hg blame`` may help track down helpful people.
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As you write your new transform or add a new kind, please consider the next
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developer. Where possible, make your change data-driven and general, so
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that others can make a much smaller change. Document the semantics of what
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you are changing clearly, especially if it involves modifying a transform
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schema. And if you are adding complexity temporarily while making a
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gradual transition, please open a new bug to remind yourself to remove the
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complexity when the transition is complete.
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Hacking Task Graphs
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-------------------
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The recommended process for changing task graphs is this:
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1. Find a recent decision task on the project or branch you are working on,
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and download its ``parameters.yml`` from the Task Inspector. This file
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contains all of the inputs to the task-graph generation process. Its
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contents are simple enough if you would like to modify it, and it is
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documented in :doc:`parameters`.
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2. Run one of the ``mach taskgraph`` subcommands (see :doc:`taskgraph`) to
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generate a baseline against which to measure your changes. For example:
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.. code-block:: none
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./mach taskgraph tasks --json -p parameters.yml > old-tasks.json
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3. Make your modifications under ``taskcluster/``.
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4. Run the same ``mach taskgraph`` command, sending the output to a new file,
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and use ``diff`` to compare the old and new files. Make sure your changes
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have the desired effect and no undesirable side-effects.
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5. When you are satisfied with the changes, push them to try to ensure that the
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modified tasks work as expected.
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Common Changes
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--------------
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Changing Test Characteristics
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.............................
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First, find the test description. This will be in
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``taskcluster/ci/*/tests.yml``, for the appropriate kind (consult
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:doc:`kinds`). You will find a YAML stanza for each test suite, and each
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stanza defines the test's characteristics. For example, the ``chunks``
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property gives the number of chunks to run. This can be specified as a simple
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integer if all platforms have the same chunk count, or it can be keyed by test
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platform. For example:
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.. code-block:: yaml
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chunks:
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by-test-platform:
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linux64/debug: 10
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default: 8
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The full set of available properties is in
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``taskcluster/taskgraph/transform/tests/test_description.py``. Some other
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commonly-modified properties are ``max-run-time`` (useful if tests are being
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killed for exceeding maxRunTime) and ``treeherder-symbol``.
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.. note::
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Android tests are also chunked at the mozharness level, so you will need to
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modify the relevant mozharness config, as well.
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Adding a Test Suite
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...................
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To add a new test suite, you will need to know the proper mozharness invocation
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for that suite, and which kind it fits into (consult :doc:`kinds`).
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Add a new stanza to ``taskcluster/ci/<kind>/tests.yml``, copying from the other
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stanzas in that file. The meanings should be clear, but authoritative
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documentation is in
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``taskcluster/taskgraph/transform/tests/test_description.py`` should you need
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it. The stanza name is the name by which the test will be referenced in try
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syntax.
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Add your new test to a test set in ``test-sets.yml`` in the same directory. If
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the test should only run on a limited set of platforms, you may need to define
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a new test set and reference that from the appropriate platforms in
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``test-platforms.yml``. If you do so, include some helpful comments in
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``test-sets.yml`` for the next person.
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Greening Up a New Test
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......................
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When a test is not yet reliably green, configuration for that test should not
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be landed on integration branches. Of course, you can control where the
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configuration is landed! For many cases, it is easiest to green up a test in
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try: push the configuration to run the test to try along with your work to fix
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the remaining test failures.
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When working with a group, check out a "twig" repository to share among your
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group, and land the test configuration in that repository. Once the test is
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green, merge to an integration branch and the test will begin running there as
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well.
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Adding a New Task
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.................
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If you are adding a new task that is not a test suite, there are a number of
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options. A few questions to consider:
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* Is this a new build platform or variant that will produce an artifact to
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be run through the usual test suites?
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* Does this task depend on other tasks? Do other tasks depend on it?
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* Is this one of a few related tasks, or will you need to generate a large
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set of tasks using some programmatic means (for example, chunking)?
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* How is the task actually excuted? Mozharness? Mach?
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* What kind of environment does the task require?
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Armed with that information, you can choose among a few options for
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implementing this new task. Try to choose the simplest solution that will
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satisfy your near-term needs. Since this is all implemented in-tree, it
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is not difficult to refactor later when you need more generality.
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Existing Kind
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`````````````
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The simplest option is to add your task to an existing kind. This is most
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practical when the task "makes sense" as part of that kind -- for example, if
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your task is building an installer for a new platform using mozharness scripts
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similar to the existing build tasks, it makes most sense to add your task to
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the ``build`` kind. If you need some additional functionality in the kind,
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it's OK to modify the implementation as necessary, as long as the modification
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is complete and useful to the next developer to come along.
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New Kind
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````````
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The next option to consider is adding a new kind. A distinct kind gives you
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some isolation from other task types, which can be nice if you are adding an
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experimental kind of task.
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Kinds can range in complexity. The simplest sort of kind uses the
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``TransformTask`` implementation to read a list of jobs from the ``jobs`` key,
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and applies the standard ``job`` and ``task`` transforms:
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.. code-block:: yaml
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implementation: taskgraph.task.transform:TransformTask
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transforms:
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- taskgraph.transforms.job:transforms
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- taskgraph.transforms.task:transforms
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jobs:
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- ..your job description here..
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Custom Kind Implementation
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``````````````````````````
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If your task depends on other tasks, then the decision of which tasks to create
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may require some code. For example, the ``upload-symbols`` kind iterates over
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the builds in the graph, generating a task for each one. This specific
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post-build behavior is implemented in the general
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``taskgraph.task.post_build:PostBuildTask`` kind implementation. If your task
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needs something more purpose-specific, then it may be time to write a new kind
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implementation.
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Custom Transforms
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`````````````````
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If your task needs to create many tasks from a single description, for example
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to implement chunking, it is time to implement some custom transforms. Ideally
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those transforms will produce job descriptions, so you can use the existing ``job``
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and ``task`` transforms:
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.. code-block:: yaml
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transforms:
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- taskgraph.transforms.my_stuff:transforms
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- taskgraph.transforms.job:transforms
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- taskgraph.transforms.task:transforms
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Similarly, if you need to include dynamic task defaults -- perhaps some feature
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is only available in level-3 repositories, or on specific projects -- then
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custom transforms are the appropriate tool. Try to keep transforms simple,
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single-purpose and well-documented!
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Custom Run-Using
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````````````````
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If the way your task is executed is unique (so, not a mach command or
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mozharness invocation), you can add a new implementation of the job
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description's "run" section. Before you do this, consider that it might be a
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better investment to modify your task to support invocation via mozharness or
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mach, instead. If this is not possible, then adding a new file in
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``taskcluster/taskgraph/transforms/jobs`` with a structure similar to its peers
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will make the new run-using option available for job descriptions.
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Something Else?
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...............
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If you make another change not described here that turns out to be simple or
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common, please include an update to this file in your patch.
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