bazel-buildkite-example

An example that builds a simple Python monorepo with Bazel and Buildkite! 🪁

This simple hello-world example uses Bazel to build and test and a Python library (a py_library package, in Bazel parlance) and a Python script (or py_binary). The binary depends on the library, and the library gets built and packaged (by Bazel) as a Python wheel.

The repo is configured with a Buildkite pipeline that combines bazel query with Buildkite dynamic pipelines to compute a pipeline definition at runtime based on the content of each commit. A Buildkite plugin also converts Bazel Event Protocol (BEP) output into Buildkite annotations and appends them to each build. Python packages are uploaded as Buildkite artifacts.

Build all packages

$ bazel build //...

INFO: Analyzed 6 targets (0 packages loaded, 0 targets configured).
INFO: Found 6 targets...
INFO: Elapsed time: 0.127s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action

Build individual packages

$ bazel build //library/...     
                                             
INFO: Analyzed 4 targets (1 packages loaded, 2167 targets configured).
INFO: Found 4 targets...
INFO: Elapsed time: 0.477s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action

$ bazel build //app/...    
INFO: Analyzed 2 targets (42 packages loaded, 417 targets configured).
INFO: Found 2 targets...
INFO: Elapsed time: 0.651s, Critical Path: 0.31s
INFO: 9 processes: 9 internal.
INFO: Build completed successfully, 9 total actions

Query for package's reverse dependencies

$ bazel query "rdeps(//..., //library/...)"

//app:main
//app:test_main
//library:hello
//library:hello_wheel
//library:hello_wheel.dist
//library:hello_wheel.publish
//library:hello_wheel_dist
//library:test_hello

Run all tests

$ bazel test //...

INFO: Analyzed 6 targets (0 packages loaded, 0 targets configured).
INFO: Found 4 targets and 2 test targets...
INFO: Elapsed time: 0.095s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
PASSED: //app:test_main
INFO: From Testing //app:test_main
==================== Test output for //app:test_main:
Hey! there's a message from the Python library: 'Hello, world!'
================================================================================
PASSED: //library:test_hello
INFO: From Testing //library:test_hello
==================== Test output for //library:test_hello:
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
================================================================================
//app:test_main                                                 (cached) PASSED in 0.1s
//library:test_hello                                            (cached) PASSED in 0.3s

Executed 0 out of 2 tests: 2 tests pass.

Run the app

$ bazel run //app:main

INFO: Analyzed target //app:main (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //app:main up-to-date:
  bazel-bin/app/main
INFO: Elapsed time: 0.245s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/app/main

The Python library says: 'Hello, world!'

Visualize a target graph

For example, to generate a PNG of the //app:main target's dependencies:

$ bazel query --noimplicit_deps 'deps(//app:main)' --output graph | dot -Tpng -o graph.png

Requires GraphViz.

Generate the Buildkite pipeline

Also annotates the build with custom Markdown driven by Bazel's BEP output:

$ python3 .buildkite/pipeline.py

{
    "steps": [
        {
            "key": "app",
            "label": ":bazel: Build and test //app/...",
            "commands": [
                "bazel test //app/...",
                "bazel build //app/... --build_event_json_file=bazel-events.json"
            ],
            "plugins": [
                {
                    "bazel-annotate#v0.1.0": {
                        "bep_file": "bazel-events.json"
                    }
                }
            ]
        },
        {
            "key": "library",
            "label": ":bazel: Build and test //library/...",
            "commands": [
                "bazel test //library/...",
                "bazel build //library/... --build_event_json_file=bazel-events.json"
            ],
            "plugins": [
                {
                    "bazel-annotate#v0.1.0": {
                        "bep_file": "bazel-events.json"
                    }
                }
            ]
        }
    ]
}

☝️ In this example, both the app and library packages were modified in the latest commit.