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Bazel Continuous Integration

Bazel uses Buildkite for continuous integration. The user interface and the orchestration of CI builds is fully managed by Buildkite, but Bazel brings its own CI machines. The buildkite folder contains all the scripts and configuration files necessary to setup Bazel's CI on Buildkite.

Bazel on Buildkite 101

When you first log into Buildkite you are presented with a list of pipelines. A pipeline is a template of steps that are executed either in sequence or in parallel and that all need to succeed in order for the pipeline to succeed. The Bazel organisation has dozens of pipelines. Here are a selected few:

pipelines

  • The bazel postsubmit pipeline builds and tests each commit to Bazel's repository on all supported platforms.
  • The bazel presubmit pipeline is triggered on every pull request to Bazel.
  • The rules_go postsubmit pipeline is triggered on every commit to the rules_go repository.
  • The TensorFlow pipeline builds and tests TensorFlow at HEAD every four hours.

Builds

When you click on a pipeline you can see the last few builds of this pipeline. Clicking on a build then gives you access to the details of the build. For example, the below image shows a failed build step on Ubuntu 16.04.

failed build step

One can see which tests failed by clicking on the Test section. In the below example, the //src/test/shell/bazel:external_path_test was flaky as it failed in 1 out of 5 runs.

flaky test

You can view the failed test attempt's test.log file in the Artifacts tab.

flaky test log

Useful Links

buildkite useful buttons

Pull Requests

Bazel accepts contributions via pull requests. Contributions by members of the bazelbuild organisation as well as members of individual repositories (i.e. rule maintainers) are whitelisted automatically and will immediately be built and tested on Buildkite.

An external contribution, however, first needs to be verified by a project member and therefore will display a pending status named Verify Pull Request.

status verify pull request

A member can verify a pull request by clicking on Details, followed by Verify Pull Request.

buildkite verify pull request

Please vet external contributions carefully as they can execute arbitrary code on our CI machines

Build and Test Results

After a pull request has been built and tested, the results will be displayed as a status message on the pull request. A detailed view is available when clicking on the corresponding Details link. Click here for an example.

pull request details

Culprit Finder

Bazel downstream projects is red? Use culprit finder to find out which bazel commit broke it!

First you should check if the project is green with the latest Bazel release. If not, probably it's their commits that broke the CI.

If a project is green with release Bazel but red with Bazel nightly, it means some Bazel commit broke it, then culprit finder can help!

Create "New Build" in the Culprit Finder project with the following environment variable:

  • PROJECT_NAME (The project name must exists in DOWNSTREAM_PROJECTS in bazelci.py)
  • PLATFORM_NAME (The platform name must exists in PLATFORMS in bazelci.py)
  • GOOD_BAZEL_COMMIT (A full Bazel commit, Bazel built at this commit still works for this project)
  • BAD_BAZEL_COMMIT (A full Bazel commit, Bazel built at this commit fails with this project)
  • (Optional) NEEDS_CLEAN (Set NEEDS_CLEAN to true to run bazel clean --expunge before each build, this will help reduce flakiness)

eg.

PROJECT_NAME=rules_go
PLATFORM_NAME=ubuntu1404
GOOD_BAZEL_COMMIT=b6ea3b6caa7f379778e74da33d1bd0ff6477f963
BAD_BAZEL_COMMIT=91eb3d207714af0ab1e5812252a0f10f40d6e4a8

Note: Bazel commit can only be set to commits after 63453bdbc6b05bd201375ee9e25b35010ae88aab, Culprit Finder needs to download Bazel at specific commit, but we didn't prebuilt Bazel binaries before this commit.

Configuring a Pipeline

Each pipeline is configured via a Yaml file. This file either lives in $PROJECT_DIR/.bazelci/presubmit.yml (for presubmits) or in an arbitrary location whose path or URL is passed to the CI script (as configured in the Buildkite settings of the respective pipeline). Projects should store the postsubmit configuration in their own repository, but we keep some configurations for downstream projects in https://github.com/bazelbuild/continuous-integration/tree/master/buildkite/pipelines.

Basic Syntax

The most important piece of the configuration file is the tasks dictionary. Each task has a unique key, a platform and usually some build and/or test targets:

---
tasks:
  ubuntu_build_only:
    platform: ubuntu1604
    build_targets:
    - "..."
  windows:
    platform: windows
    build_targets:
    - "..."
    test_targets:
    - "..."

If there is exactly one task per platform, you can omit the platform field and use its value as task ID instead. The following code snippet is equivalent to the previous one:

---
tasks:
  ubuntu1604:
    build_targets:
    - "..."
  windows:
    build_targets:
    - "..."
    test_targets:
    - "..."

Advanced Features

There are more advanced mechanisms for configuring individual tasks:

  • The CI script can run arbitrary commands before building or testing. Simply add the batch_commands (Windows) or shell_commands field (all other platforms).
  • The run_targets field contains a list of Bazel targets that should be run before building.
  • The build_flags and test_flags fields contain lists of flags that should be used when building or testing (respectively).
  • You can specify a display name in the name field. The resulting job will display this value and an emoji that represents the platform.
---
tasks:
  ubuntu1404:
    shell_commands:
    - rm -f obsolete_file
    run_targets:
    - "//whatever"
    build_flags:
    - "--define=ij_product=clion-latest"
    build_targets:
    - "..."
    test_flags:
    - "--define=ij_product=clion-latest"
    test_targets:
    - ":clwb_tests"
  windows:
    name: "some :emoji:"
    batch_commands:
    - powershell -Command "..."
    build_targets:
    - "..."

Legacy Format

Most existing configuration use the legacy format with a "platforms" dictionary:

---
platforms:
  ubuntu1404:
    build_targets:
    - "..."
    test_targets:
    - "..."

The new format expects a "tasks" dictionary instead:

---
tasks:
  arbitrary_id:
    platform: ubuntu1404
    build_targets:
    - "..."
    test_targets:
    - "..."

In this case we can omit the platforms field since there is a 1:1 mapping between tasks and platforms. Consequently, the format looks almost identical to the old one:

---
tasks:
  ubuntu1404:
    build_targets:
    - "..."
    test_targets:
    - "..."

The CI script still supports the legacy format, too.

Using a specific version of Bazel

The CI uses Bazelisk to support older versions of Bazel, too. You can specify a Bazel version for each pipeline (or even for individual platforms) in the pipeline Yaml configuration:

---
bazel: 0.20.0
platforms:
  windows:
    build_targets:
    - "..."
  macos:
    build_targets:
    - "..."
  ubuntu1404:
    bazel: 0.18.0
    build_targets:
    - "..."
[...]

In this example the jobs on Windows and MacOS would use 0.20.0, whereas the job on Ubuntu would run 0.18.0. Please see the Bazelisk documentation for a list of all supported version values.

Running Buildifier on CI

For each pipeline you can enable Buildifier to check whether all BUILD, BUILD.bazel and .bzl files comply with the standard formatting convention. Simply add the following code to the top of the particular pipeline configuration:

---
buildifier: true
[...]

As a consequence, every future build for this pipeline will contain an additional "Buildifier" step that runs the latest version of Buildifier in "lint" mode.