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Bazel Remote Caching

*** note NOTE: Check with your organization to see if this feature is available.

Packages that build under Bazel have the ability to interact with a remote cache service, allowing faster builds. Since the use of a cache comes with a variety of concerns including cost, latency, and security, the decision whether to enable this feature will be made by individual organizations. Google will use a remote cache hosted in RBE, but another option or no remote cache at all might be the right decision for your organization.

Available Remote Caches

https://bazel.build/remote/caching provides an overview of how remote caching works in Bazel and lists a few options (though there are others). If your organization has not yet configured a remote cache server/service, work with the org to choose one to use and to procure/configure it.

Configuring Bazel to use the remote cache

Specify settings such as the following in a make.conf file that will be loaded by your Portage profile for your builds:

Note that BAZEL_REMOTE_CACHE_INSTANCE_NAME is only needed when using the RBE remote cache, and CHROMEOS_CI_USERNAME is only needed if you're running builds on CI hosts you control and they should write to the cache.

User setup

In addition to the config settings listed above, a user looking to leverage the remote Bazel cache for locally-executed builds needs to run the following command to store credentials for Bazel to use:

(outside)
$ gcloud auth application-default login

This will store authentication credentials in ~${HOME}/.config/gcloud that will be mapped into the chroot, and which will allow Bazel executions within your builds to authenticate as you to RBE to access the remote cache it hosts. If you use a remote cache that is not hosted in Google Cloud, you will need this file to exist in order to enable remote cache interaction, but can just touch ~${HOME}/.config/gcloud/application_default_credentials.json so it exists but not worry about its content.

Packages

Remote caching is currently enabled only for the sys-cluster/fcp package. This feature will eventually be enabled for all Bazel-built packages within ChromeOS.