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Fuchsia Continuous Integration Configuration

This repository contains Fuchsia's configuration files for LUCI, the continuous integration system that we share with the Chromium project.

You can configure LUCI to:

  • Run scheduled jobs to continuously build and test code in your repo.
  • Run a commit queue to block commits in Gerrit that would break your build or any builds that depend on your code.

Buildbucket configuration

Buildbucket is LUCI's build queue. We use Buildbucket with Swarming, which is a system for centrally scheduling jobs to run on different machines. Swarming is the same system that the Chromium project uses.

cr-buildbucket.cfg defines a set of builders for Fuchsia. A builder basically defines a task to run, and a type of machine to run it on.

Anatomy of a builder

Here's one of our builders, as an example:

builders {
  category: "Fuchsia"
  name: "fuchsia-x86_64-linux-debug"
  mixins: "fuchsia"
  dimensions: "os:Linux"
  recipe {
    properties: "target:x86-64"
    properties: "build_type:debug"

This builder has:

  • A category of similar builders that it belongs to. In this case, it builds all of Fuchsia, so it's part of the “Fuchsia” category.
  • A unique name.
  • A set of dimensions (in this case just one) specifying what kind of machine can handle it.
  • Information about what recipe to run. A recipe is a Python script that uses the recipes framework to define a series of commands to run on the machine. We maintain the Fuchsia recipes in the infra/recipes repo. There are two properties here, which will be passed into the recipe when it runs. One of them says that the build target is x86_64, and the other one says that it‘s a debug build. It’s up to the recipe to interpret these, and you can read the recipe code to understand how they get used.

There‘s also reference to a builder mixin, which is a way to reuse configuration between builders. In this case, we’re using the “fuchsia” mixin, which is defined like this:

builder_mixins {
  name: "fuchsia"
  recipe {
    name: "fuchsia"
    properties: "manifest:fuchsia"

This mixin provides additional information about the recipe: it says which recipe to use (“fuchsia”, which corresponds to a file called in the recipes repo) and it gives an additional property: it tells the recipe to use the Jiri manifest named “fuchsia” when it checks out the code.

And finally, this builder is in a bucket, which is a grouping of builders with the same set of ACLs. We have two buckets:

  • The continuous bucket is for continuously-running post-commit builds.
  • The try bucket is for testing changes on the commit queue.

This particular builder is in the continuous bucket, which declares a set of defaults for all of its builders:

builder_defaults {
  swarming_tags: "allow_milo:1"
  dimensions: "pool:Fuchsia-try"
  dimensions: "netboot_devices:0"
  recipe {
    repository: ""
    properties: "remote:"

There are more machine dimensions here, including the machine pool, since the continuous jobs and try jobs use different pools. There's also the location of the recipes repos, and the “remote” property for the recipe, which points to the Fuchsia manifest repo.

Adding builders for a new project

Since you want to schedule continuous builds and a commit queue, you need to add the following:

  • A builder mixin with all of the common builder parameters for your project.
  • A builder in the continuous bucket for each variation that you want to run. You probably want at least one each for aarch64 and x86_64.
  • A corresponding builder in the try bucket for each variation.
  • Any other mixins you need to make the configuration code easy to manage. Mixins are allowed to inherit from other mixins, so you can layer them if you need to.

LUCI scheduler configuration

luci-scheduler.cfg tells LUCI which builds to run continuously. It consists of multiple job declarations, each one of which refers to a builder using the names defined in the Buildbucket configuration. This is basically cron for LUCI, and you can use cron expressions in the schedule parameter of each job, as well as expressions like: “with 10m interval”.

Commit queue configuration

The repositories directory of this repo has a directory for every Fuchsia repo that has a commit queue. If you want to add a commit queue for your repo, create a directory here, copy the refs.cfg and cq.cfg files from an existing directory, and make the necessary changes.


This is a magical workaround for legacy issues. It's basically the file that bootstraps the commit queue configuration. Just make sure that config_path points to your new directory. You also need to make sure this file is picked up in the global LUCI configuration, which is stored in a Google-internal repo. Ask someone from the Fuchsia infrastructure team for help with this step.


This the configuration file for the Chromium Commit Queue, which is a thing that watches Gerrit for CLs it can build, test, and commit.

We always use the same cq_status_url for Fuchsia, and the git_repo_url is specific to the repo. cq_name is a unique identifier for the project's CQ, and it can usually just be the same as the all-lowercase name of the repo.

A LUCI commit queue configuration consists of one or more verifiers, which are steps that must pass before committing is allowed. The basic configuration for a Fuchsia CQ is a single try-job verifier, which means that every commit must pass a check that involves running a set of builders from the Buildbucket configuration.

Under buckets, we always specify that we are using “luci.fuchsia.try”. Add an entry here for every builder in the try bucket that you want to run on the CQ for this repo. This could include builders specific to your repo, as well as anything else you don't want to break when you commit things, such as the main Fuchsia build.

The gerrit_cq_ability section defines permissions for who can use the CQ, and it's the same for all Fuchsia repos.

Testing your configuration

Right now the only real way to test your LUCI configuration is to commit a change and see if it works, then commit a fix if it doesn't. Once your configuration gets committed, your scheduled builds should start showing up on the LUCI Scheduler web interface.

To test the commit queue, create a new commit for your project in Gerrit. The contents of the commit don't matter, since you will only be doing a dry run.

If you have the right permissions in Gerrit and you are using PolyGerrit, you should see a button in the top right that says “CQ Dry Run”. Click it, and soon you should see a comment from the CQ bot, with a link to its progress. Check to see if it completes all the builds you configured in the above steps.