Bazel Compose

bazel_compose is docker-compose for bazel. It allows you to use a docker-compose.yml-like file to describe how to start and run many container images.

Usage

Define a bazel-compose.yml with contents similar to the following:

version: '2.0'
services:
  test:
    image: //something

Now run the following command:

# From Bazel
bazel run //caper/bazel_compose -- $PWD
bazel run //caper/bazel_compose -- $PWD --follow <container> # Only tails logs of specific container

# From binary as installed below
bazel-compose
bazel-compose --follow <container> # Only tails logs of a specific container

After a few moments you will see the logs from your container. Your container (//something) has just been built & tagged (bazel run //something -- --norun) and then it was started (docker-compose up -d test). Now, whenever you edit the files that go into producing //something your container will automatically be rebuilt and restarted.

Note: When you have many containers startup time might be more than a few moments. If you have started & connected your IDE to bazel, though, this should not be a problem as the IDE makes the same calls we make to the bazel daemon.

Installation

1. Install ibazel

   wget -O ibazel https://github.com/bazelbuild/bazel-watcher/releases/download/v0.13.2/ibazel_linux_amd64
   chmod +x ibazel
   sudo mv ibazel /usr/local/bin/ibazel

2. Install bazel-compose

   sudo apt install python3
   git clone git@github.com:gravypod/bazel_compose.git
   cd bazel_compose
   bazel build //caper/bazel_compose:bazel_compose.par
   sudo cp bazel-bin/caper/bazel_compose/bazel_compose.par /usr/local/bin/bazel-compose
   sudo chmod +x /usr/local/bin/bazel-compose

3. cd into your workspace and run bazel-compose to start everthing.

Implementation

This code is really a wrapper around:

1. bazel
2. ibazel
3. docker-compose

On startup we read in the bazel-compose.yml from the cwd. We then parse this file and look for anything that looks like a bazel targets. We then give those targets to ibazel and ask ibazel to build these targets whenever files they depend on change. Once we see a change we check the .digest file from the container image to make sure that the contents of the container has actually changed. Once we are sure there has been a change we tell bazel to tag the image on the host system using bazel run //something -- --norun. We then tell docker-compose to restart your image.