Infrastructure

Chromium DevTools has an infrastructure component that consists of recipes that define how to build and test the frontend in CQ and CI plus a set of rollers to automate dependency updates.

Overview of the code

The configuration for the DevTools infrastructure is in the infra/config branch. The recipes are located in the chromium/tools/build repository.

Luci-config app is consuming the configuration from infra/config. You can force refresh from the app. DevTools configuration is located here.

Checking out the infra config branch

mkdir devtools-infra
cd devtools-infra
fetch devtools-frontend
cd devtools-frontend
git checkout infra/config

Run git clean -fd and remove the rest of the remaining files from the main branch.

Submitting an infra config change

First, create a branch for the change and set upstream to the infra/config:

git new-branch branch-name --upstream_current

• buckets/try.star: configurations for default try-jobs for a CL.
• buckets/try-misc.star: configurations for additional builders that can be manually added to CLs in Gerrit or via git cl try.
• buckets/cpp_debugging_extension.star: configurations for the C++ debugging extension tests.
• buckets/serving_app.star: configurations for the DevTools server app.
• buckets/ci.star: configurations to run on the main branch after a CL is submitted also known as CI or Waterfall builders.
• buckets/ci-hp.star: configurations for the highly privileged builders that rolls dependencies.

After you update a .star file, re-generate generated files using lucicfg main.star.

These .star definitions roughly correspond to the CI console view https://ci.chromium.org/ui/p/devtools-frontend.

Run git cl upload. Infra changes are submitted similar to the regular frontend CLs using git cl upload. After a review on Gerrit, the change will be merged into the infra branch.

Note that the changes made in the CL are not picked up by the bots before the change is merged. After the CL is merged, the change will be deployed to the bots.

Submitting a recipe change

Follow the instructions at https://chromium.googlesource.com/chromium/tools/build/+/refs/heads/main/recipes/README.md and upload a CL for chromium/tools/build.

Updating test commands in the infrastructure

The DevTools recipes are defined in chromium/tools/build repository. Once a change is made there, the recipes are packaged as a cipd package and the infra/config data defines how to fetch that cipd package. The recipes are bundled by https://ci.chromium.org/ui/p/chrome/builders/official.infra/recipe-bundler.

DevTools recipes live at https://chromium.googlesource.com/chromium/tools/build/+/refs/heads/main/recipes/recipes/devtools/.

Determining if a change needs to run tests

The try.star file in the infra/config branch contains the logic that determines which builders are needed to verify a CQ. See custom_locationsfilters for the current logic.

Some of the filters currently in use are:

• cpp_debug_extension builders only trigger on changes related to the extension
• dtf_check_no_bundle builder only trigger on GN changes
• all other builders will not trigger if only documentation files are updated

Branch cutting process

At the end of every release cycle Chromium will cut a new branch for the current release.

The branch cut process for DevTools is as simple as updating the beta, stable and extended branch numbers in infra/config (example CL):

• checkout infra/config branch
• pull and create a new branch ([see](#Submitting an infra config change))
• update the definitions.star file:
  • extended number gets updated every second release:
    • if the extended number is equal to the stable number, then update extended to the current beta number
    • otherwise update it to the current stable number
  • stable number updates to the current beta number
  • beta number updates to the Chromium beta brunch number (see)
• regenrate the cfg files (lucicfg main.star), commit, upload and add liviurau@chromium.org as reviewer (or another infra team member)

Changing these numbers will reconfigure the CI and CQ for beta, stable and extended branches. After landing the change the three branch consoles will get reset.

Toggle tree closing behaviour on CI builders

Sometimes we might need to avoid a misbehaing builder closing the tree. Or maybe we need to make a FYI builder a tree closer.

To do so find your builder buckets/ci.star file and toggle the notification_muted property (defaults to False if not present). Setting the property to True/False will remove/add the tree closer notifier for this builder. Make sure you regenerated the cfg files and upload your changes. Example.

Toggle blocking behaviour of CQ builders

CQ builders come in 3 flavors:

• regular try builder: will always prevent a CL from landing when the builder fails
• includable builder: will run only if expecitly added to a CQ run and will prevent a CL from landing if the builder fails
• experimental builder: will run a percentage of the times it gets an oppotunity run and will not block the CL from landing if the builder fails

To toggle this behaviour you need to edit buckets/try.star file (example):

• all builders must be enumetated in cq_builders.devtools_builders list
• to make a builder includable add it's name cq_builders.includable_only_builders list; remove it from the list to make it a regular builder
• to make a builder experimental add it's name cq_builders.experiment_builders dictionary together with the desired experiment rate percentage; remove it from the list to make it a regular builder

Adding a new builder in CQ

To add a new try-builder edit the buckets/try.start file to call one of the existing functions that generate builder definitions:

• try_builder used for builder with recipes that do not orchestrate other builders:
  • build only builders (dtf_check_no_bundle)
  • chromium builders (devtools_frontend_linux_blink_light_rel_fastbuild)
• try_pair used for builders with orchestrating recipes (delegates to a compilator builder before delegating testing to swarming)

Alternatively define your own builder function and call it for the instances you need (see presubmit_builder and cpp_debug_extension_try).

You will need add your new builder to the cq_builders.devtools_builders list.

To control the CL blocking behaviour of your builder see above.

To control if the builder should be not present in the CQ for branches, add your builder to cq_builders.chromium_builders list.

Adding a new builder in CI

To add a new try-builder edit the buckets/ci.start file to add a new builder_descriptor to the builders of generate_ci_configs function call.

In your descriptor decide for the name of builder, the recipe, any other custom properties you might need and for which configurations (consoles) to include your builder (ci stands for the main waterfall console). Example.

Anatomy of a CQ build

In CQ the builders that get most attention are dtf_*_rel builders. These builders run the devtools/trybot_tester recipe and are responsible with building DevTools Frontend and running our tests.

Below is a detailed description of what happens in such a build:

• The recipe will perform the bot_update and gclient runhooks step where the tip-of-tree for devtools-frontend gets checked out, your changes get patched on top of it and dependencies get updated.
• The compilator bot get triggered (initialization step)
• We wait for the compilator bot to finish. This bot is responsible for the actual build of devtools-frontend.
  • It does a bot_update of its own
  • Generates the GN files (gn step)
  • Compiles (compile) the project
  • Reads the e2e_non_hosted test lists
  • Creates a CAS archive with project and the compilation output
  • Ouputs the compilator_properties
• Once the compilator is done we read the compilator_properties to find
  • the cas_digest to be used when triggering tests on swarming
  • the e2e_non_hosted_test_list for sharding the e2e tests execution
• Write the e2e test list at the location where building would have written it
• The default test run phase starts at Run tests step:
  • We trigger all tests on swarming in parallel (Trigger Tests) substep.
    • For all types of tests we calculate the command we want to run on swarming and trigger a task with that command and the collected CAS digest
    • Before calculating the command for e2e test we read the test list and and split it in a number of shards. Each shard will have the allocated tests specified in the command.
  • We wait for all swarming task to complete
• Next we re-run the failed tests in attemt to exonerate their initial failures (Flake exonaration attempt step):
  • We query ResultDB for any tests that might have failed
  • We collect the failed test names and contruct new commands to re-run them on new swarming tasks
  • We wait for all swarming task to complete
• Finally we will stress test the tests that were added/modified by the current CL in the Detect flakes in new tests step
  • Run git diff to determine which tests were added/modifed
  • Construct the command to be run on swatming
  • Trigger and wait for the swarming tasks to finish
• Calculate the outcome of the builder:
  • fail the builder if tests failed in the default run and the exoneration run was unsuccesful
  • fail the builder if tests failed in the deflaking phase
  • otherwise report build as passing

Common build failures

The first place where a build usualy fails is on bot_update and this usually happens because your changes cannot be applied on top of the current tip-of-tree. Rebase your CL and solve any merge conflicts and this failure will go away.

Another common failure is a compilation failure. You can insepct the compilator builder (dtf_*_compiler_rel) separately by following the link next to the compilator steps step.

If you have too many tests failing in the default phase the exoneration phase gets skipped.

A test might not get exonerated in your build even if your CL does not touch anything related to it. The exoneration phase will re-run previously faling tests a number of times and at any point the test passes the tests gets exonerated. Therefore a test can have a recent history of getting exonerated even if it consitently failed 4 times out of 5 runs for some time. Try to correlate your failure with a luci-analysys report on this test and skip it untill the flakiness gets resolved.