New test environments

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From time to time, there rises a need to upgrade the underlying operating system of a platform. This need arises in sync with new major releases of various operating systems that form part of the CI infrastructure.

For instance, as of 2019-08-07, all Firefox builds for Linux are executed on Ubuntu 16.04.5 docker containers. In other words, the version of Linux distribution used for testing is at least 2 major releases behind the likely dominant version on the market, which is Ubuntu 18.04.

Upgrade of the underlying operating system version has been, in the past, considered a large undertaking often taking upwards of 6 months. This causes a chicken-and-egg problem where regular upgrades do not occur due to the perceived amount of work, which in turn causes the amount of issues to multiply once the upgrade is finally tackled.

The aim of this document, and process is to establish a standardized process which can be used by anyone in Mozilla engineering to perform operating-system upgrades.

Task Overview

Broadly speaking, the following discrete phases are involved when adding new platforms.

  • preparation work - docker/virtual
    • responsibility: CI-A

all tasks below can be parallelized

  • begin greening process - file bugs
  • address issues with test case/platform
    • responsibility: developers
  • create, review and land migration patches

Preparation work

The underlying test environment must first be set up.

At Mozilla there are two different machine types, both self-explalanatory:

  • virtual
  • hardware

Both require different approaches.


The availability of test hardware is outside of CI-A (and therefore your) control. With some exceptions, Mozilla's server farms are managed by the Release Engineering team. They work in concert with CI-A to develop a plan to upgrade and maintain test hardware.

For instance, the OS upgrade from macosx1010 to macosx1014 was handled by :dividehex. See Bug 1530474.

With some exceptions, CI-A is not particularly involved in this process.


For virtual test environment, it is within the scope of CI-A work.


Both examples involve the creation of new docker images that run on AWS instances.

Enable platform on taskgraph

The first real step of any new test environment is to enable the test platform on Tryserver.

At the bare minimum, ensure the taskgraph is sound with each step. This can be verified using ./mach taskgraph full -v

Enable build

This step may have already been performed by other teams (eg. Releng). If so, skip to the next step.

First, the platform must have builds enabled before tests can be run.

Within the taskcluster/ci/build directory, edit the appropriate YAML file for the platform. For example, if adding a new Windows build type, edit taskcluster/ci/build/windows.yml.

Define all of the required attributes, using existing configurations as a template.

Example with windows10-aarch64 builds:


   description: "AArch64 Win64 Opt"
       product: firefox
       job-name: win64-aarch64-opt
       enable-full-crashsymbols: true
       platform: windows2012-aarch64/opt
       symbol: B
       tier: 1
   worker-type: b-win2012
       max-run-time: 7200
           TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win64/aarch64.manifest"
           PERFHERDER_EXTRA_OPTIONS: aarch64
       actions: [get-secrets, build]
       options: [append-env-variables-from-configs]
       script: mozharness/scripts/
       secrets: true
           - builds/
           - builds/
           - builds/
           stage_platform: win64-aarch64
           mozconfig_platform: win64-aarch64
           - win64-clang-cl
           - win64-rust
           - win64-rust-size
           - win64-cbindgen
           - win64-sccache
           - win64-nasm
           - win64-node


Bug 1503366


  • has meta bug been created in Bugzilla in Firefox Build System::Task Configuration component?
  • does ./mach taskgraph full succeed?
  • does build successfully complete on Tryserver?

Worker configuration

This step may have already been performed by other teams (eg. Releng), or not required at all (eg. OS upgrade). If so, skip to the next step.

Once the build task has been successfully enabled, test workers must be defined.

There are several files that need to have the new platform added in order to satisfy the taskgraph algorithm:

  • taskcluster/taskgraph/transforms/
  • taskcluster/taskgraph/util/

Check and add the new platform details in the following categories:

  • worker types
  • tiers
  • treeherder name translations


Bug 1527469
Bug 1550826 - a more involved example


  • does ./mach taskgraph full succeed?

Test configuration

Once worker configuration is complete, test configuration must be added for the new platform.

Several files must be modified to support running tests against the new platform:

  • taskcluster/ci/test/test-platforms.yml
  • taskcluster/ci/test/test-sets.yml

The following is an example platform where the full suite of desktop Firefox tests are run, and thus the list of defined tests are long. Depending on the nature of the platform, the list of tests will vary.

Example test-sets.yml:


   - cppunit
   - crashtest
   - firefox-ui-functional-local
   - firefox-ui-functional-remote
   - gtest
   - jittest
   - jsreftest
   - marionette
   - mochitest
   - mochitest-a11y
   - mochitest-browser-chrome
   - mochitest-chrome
   - mochitest-devtools-chrome
   - mochitest-devtools-webreplay
   - mochitest-gpu
   - mochitest-media
   - mochitest-remote
   - mochitest-webgl1-core
   - mochitest-webgl1-ext
   - mochitest-webgl2-core
   - reftest
   - telemetry-tests-client
   - test-verify
   - test-verify-gpu
   - test-verify-wpt
   - web-platform-tests
   - web-platform-tests-reftests
   - web-platform-tests-wdspec
   - xpcshell

Example test-platforms.yml:


   build-platform: macosx64-shippable/opt
       - macosx1014-64-tests
       - macosx64-talos
       - desktop-screenshot-capture
       - awsy
       - raptor-chromium
       - raptor-firefox
       - raptor-profiling
       - marionette-media-tests
       - web-platform-tests-wdspec-headless

Exact list of tests will vary depending on the platform. It is not possible to run cppunit on android platforms, for example.

Note that:

  • list of tests defined in test-sets.yml is used in test-platforms.yml
  • build-platform attribute in test-platforms.yml should match the build name chosen in the previous step


Bug 1527469
Bug 1550826


  • does ./mach taskgraph full succeed with test sets and test platforms defined?
  • do the tests show up in the try fuzzy selector?

Obtain baseline

Once build and tests are enabled on Tryserver, it is time to run a baseline push to take inventory of suites that pass and fail.

Using ./mach try fuzzy --no-artifact --rebuild 10, push tests belonging to the new platform to the Tryserver. Do not use artifact builds for the baseline push as some test results (outside of the compiled tests such as cppunit) are affected by the artifact build.

Once the checklist is complete, create a diff on Phabricator and have it reviewed by

  • intermittent-reviewers
  • triage owner or test owner


Debian 10


  • does the build succeed?
  • are all tests scheduled?
  • how many tests abort/retry?
  • how many tests pass?
  • how many tests fail?
  • what test chunks appear intermittent?
  • for failed tests, is it due to platform configuration issues or legitimate failures?

Green up tests

Once the build and tests are running on Tryserver, it is time to begin greening the tests. This task is typically the one that consumes the most time as well as having subtle nuances in how the task should be handled.

For this step, it is possible to have several engineers each tackle a selected suite/subsuite:

  • engineer A
    • mochitest-browser-chrome
    • gtest
  • engineer B
    • web-platform-tests
    • reftests

Make sure to create meta bugs for each broad category in Bugzilla. A typical breakdown:

  • platform meta bug
    • xpcshell
    • mochitest
    • compiled tests
    • reftest/crashtest
    • web-platform-tests (including web-platform variants of reftests/crashtests)
    • miscellaneous tests

Mochitest is a particularly large suite and has many subsuites, so in practice a separate meta bug for each mochitest subsuite could be useful.

Reference: Ubuntu1804 meta bug.

Reporting failures

Use Treeherder where possible when logging failures - this allows all sorts of backend connections to be made, and also nicely includes the debug logs and such if available.

There are some nuances to consider when logging failures; notably, has this bug been reported before? Where possible, reduce duplicate bugs in the system as much as possible.

Example workflows in different situations will be given below.

Example (with previously logged bug that match the description)

  • click on the chunk with failures, and wait for Failure Summary pane to open
  • open an instance of the run logs in a new tab/window
  • in the nested list below the failure will be a list of bugs that Treeherder thinks match the error description, based on the bug title.
  • find the bug that best matches the error description from the current run. Quickly check the logs in both the current run and the bug to ensure it describes the same issue.
  • if satisfied, click on the pushpin icon.
  • in the new pane that pops above the Failure Summary, click on Save.

Example (no bugs match description or no bugs filed for particular failure)

  • follow the same steps as above, until the second to last step.
  • open an instance of the live_backing.log in a separate tab.
  • since none of the bugs suit the description or no bugs have been filed for this particular failure, click on the bug icon beside the error description.
  • a new overlay will show titled Intermittent Bug Filer.
  • use ./mach bugzilla-component file-info <file_path> to identify the bug component.
  • prefix the bug title with an appropriate name for the platform.
  • in the body, specify the platform, subsuite and paste the relevant portion of the log.
  • fill in the blocks, depends on and see also bug as appropriate.

Needinfo test owners

This is the most important part of the process.

Get the bug in front of the triage owner, feature owner or the test developer and provide as much information as possible relating to nature of the bug, reproduction steps, any extra commands or steps necessary, etc.

Set a needinfo request and ask them to chime in. If no response is received after some time, usually a week, mark some activity to 'bump' the bug.

Depending on the migration timeframe, this may happen anywhere between 2-4 times.


  • meta bugs created in Bugzilla?
  • responsibilities for suites/subsuites/chunks divided amongst engineers (if multiple engineers assigned)?
  • for each failure in a chunk, associate an existing bug or create a new bug.
  • for each bug created, has triage owner been notified with needinfo describing the nature of the problem?

Annotate failing tests

It is not always possible for developers to address an issue, especially if nature of the failure is deemed to be lower in priority.

Given that the new test environment setup should be time-bounded, this means that often it becomes necessary to disable the particular test and/or manifest files.


macosx1014 - D36985

In the example above, it became necessary to disable certain tests that continued to fail on macosx1014 despite the test/feature owner being notified of the failure for several weeks.

Generally speaking, the following steps should be taken prior to test being disabled:

  • if a bug has not been filed, please do so.
  • needinfo the triage/test/module owner.
  • comment on the bug to maintain activity every 2-3 weeks, preferably with status update and newer logs.

If no movement occurs:

  • annotate the test case with narrowest possible criteria.
  • include comment that specifies platform shorthand and bug number.
  • submit to phabricator.
  • submit a Try push with the proposed patch applied to verify the work.

Be sure to include in the review the test/module/triage owner and intermittent-reviewers group.


  • has triage/test/module owner been needinfo'd?
  • has consistent activity been reported on the bug for a few weeks?
  • is the annotation using narrowest possible criteria?
  • has a bug number been added to the comment for the annotation?
  • has the owner been notified in the phabricator patch?

Migrate over a test suite