2018-04-11 18:13:05 +03:00
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Partial Update Generation
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=========================
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Overview
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--------
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Windows, Mac and Linux releases have partial updates, to reduce
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the file size end-users have to download in order to receive new
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versions. These are created using a docker image, some Python,
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``mbsdiff``, and the tools in ``tools/update-packaging``
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The task has been called 'Funsize' for quite some time. This might
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make sense depending on what brands of chocolate bar are available
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near you.
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How the Task Works
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------------------
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Funsize uses a docker image that's built in-tree, named funsize-update-generator.
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The image contains some Python to examine the task definition and determine
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what needs to be done, but it downloads tools like ``mar`` and ``mbsdiff``
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from either locations specified in the task definition, or default mozilla-central
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locations.
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The 'extra' section of the task definition contains most of the payload, under
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the 'funsize' key. In here is a list of partials that this specific task will
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generate, and each entry includes the earlier (or 'from') version, and the most
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recent (or 'to') version, which for most releases will likely be a taskcluster
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artifact.
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2018-04-18 17:01:36 +03:00
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.. code-block:: json
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2018-04-11 18:13:05 +03:00
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{
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2018-09-25 22:06:08 +03:00
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"to_mar": "https://tc.net/api/queue/v1/task/EWtBFqVuT-WqG3tGLxWhmA/artifacts/public/build/ach/target.complete.mar",
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2018-04-11 18:13:05 +03:00
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"product": "Firefox",
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"dest_mar": "target-60.0b8.partial.mar",
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"locale": "ach",
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"from_mar": "http://archive.mozilla.org/pub/firefox/candidates/60.0b8-candidates/build1/update/linux-i686/ach/firefox-60.0b8.complete.mar",
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"update_number": 2,
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"platform": "linux32",
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"previousVersion": "60.0b8",
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"previousBuildNumber": "1",
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"branch": "mozilla-beta"
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2018-06-27 08:42:08 +03:00
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}
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2018-04-11 18:13:05 +03:00
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The 'update number' indicates how many released versions there are between 'to' and the current 'from'.
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For example, if we are building a partial update for the current nightly from the previous one, the update
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number will be 1. For the release before that, it will be 2. This lets us use generic output artifact
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names that we can rename in the later ``beetmover`` tasks.
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Inside the task, for each partial it has been told to generate, it will download, unpack and virus
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scan the 'from_mar' and 'to_mar', download the tools, and run ``make_incremental_update.sh`` from
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``tools/update-packaging``.
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If a scope is given for a set of temporary S3 credentials, the task will use a caching script,
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to allow re-use of the diffs made for larger files. Some of the larger files are not localised,
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and this allows us to save a lot of compute time.
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For Releases
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------------
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Partials are made as part of the ``promote`` task group. The previous
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versions used to create the update are specified in ship-it by
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Release Management.
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Nightly Partials
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----------------
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Since nightly releases don't appear in ship-it, the partials to create
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are determined in the decision task. This was controversial, and so here
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are the assumptions and reasons, so that when an alternative solution is
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discovered, we can assess it in context:
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1. Balrog is the source of truth for previous nightly releases.
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2. Re-running a task should produce the same results.
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3. A task's input and output should be specified in the definition.
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4. A task transform should avoid external dependencies. This is to
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increase the number of scenarios in which 'mach taskgraph' works.
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5. A task graph doesn't explicitly know that it's intended for nightlies,
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only that specific tasks are only present for nightly.
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6. The decision task is explicitly told that its target is nightly
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using the target-tasks-method argument.
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a. From 2 and 3, this means that the partials task itself cannot query
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balrog for the history, as it may get different results when re-run,
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and hides the inputs and outputs from the task definition.
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b. From 4, anything run by 'mach taskgraph' is an inappropriate place
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to query Balrog, even if it results in a repeatable task graph.
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c. Since these restrictions don't apply to the decision task, and given
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6, we can query Balrog in the decision task if the target-tasks-method
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given contains 'nightly', such as 'nightly_desktop' or 'nightly_linux'
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Using the decision task involves making fewer, larger queries to Balrog,
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and storing the results for task graph regeneration and later audit. At
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the moment this data is stored in the ``parameters`` under the label
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``release_history``, since the parameters are an existing method for
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passing data to the task transforms, but a case could be made
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for adding a separate store, as it's a significantly larger number of
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records than anything else in the parameters.
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Nightly Partials and Beetmover
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------------------------------
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A release for a specific platform and locale may not have a history of
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prior releases that can be used to build partial updates. This could be
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for a variety of reasons, such as a new locale, or a hiatus in nightly
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releases creating too long a gap in the history.
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This means that the ``partials`` and ``partials-signing`` tasks may have
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nothing to do for a platform and locale. If this is true, then the tasks
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are filtered out in the ``transform``.
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This does mean that the downstream task, ``beetmover-repackage`` can not
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rely on the ``partials-signing`` task existing. It depends on both the
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``partials-signing`` and ``repackage-signing`` task, and chooses which
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to depend on in the transform.
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If there is a history in the ``parameters`` ``release_history`` section
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then ``beetmover-repackage`` will depend on ``partials-signing``.
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Otherwise, it will depend on ``repackage-signing``.
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This is not ideal, as it results in unclear logic in the task graph
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generation. It will be improved.
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