README.md

Buildbarn Remote Execution

Translations: Chinese

This repository provides tools that can be used in combination with the Buildbarn storage daemon to add support for remote execution, allowing you to create a build farm that can be called into using tools such as Bazel, BuildStream and recc.

This repository provides three programs:

• bb_scheduler: A service that receives requests from bb_storage to queue build actions that need to be run.
• bb_worker: A service that requests build actions from bb_scheduler and orchestrates their execution. This includes downloading the build action's input files and uploading its output files.
• bb_runner: A service that executes the command associated with the build action.

Most setups will run a single instance of bb_scheduler and a large number of pairs of bb_worker/bb_runner processes. Older versions of Buildbarn integrated the functionality of bb_worker and bb_runner into a single process. These processes were decomposed to accomplish the following:

• To make it possible to use privilege separation. Privilege separation is used to prevent build actions from overwriting input files. This allows bb_worker to cache these files across build actions, exposing it to the build action through hardlinking.
• To make execution pluggable. bb_worker communicates with bb_runner using a simple gRPC-based protocol. One could, for example, implement a custom runner process that executes build actions using QEMU user-mode emulation.
• To work around a race condition that effectively prevents multi-threaded processes from writing executables to disk and spawning them. Through this decomposition, bb_worker writes executables to disk, while bb_runner spawns them.

This repository provides container images for each of these components. For bb_runner, it provides two images: bb_runner_bare and bb_runner_installer. bb_runner_bare has no userland/linux install, it just has the bb_runner executable. Typically the actions that will run on a runner do expect some userland to be installed.

It would be nice if you could just use any image of your choosing as the image that your build actions will run on. Like using Ubuntu 16.04 image, to take advantage of the fact that bazel project provides ready-to-use toolchain definitions for them.

What makes that tricky is that that image will not have bb_runner installed. This is where bb_runner_installer image comes in. It doesn't actually install anything, but it provides the bb_runner executable through its filesystem. You have to configure your orchestration of choice to mount this filesystem from bb_runner_installer into the image of your choice that you want to run on. This way you can use a vanilla image and just run the bb_runner executable from Buildbarn's provided container. There's a few tricks to check if the volume is already available, you can see an example of how to do this in the docker-compose example.

Please refer to the Buildbarn Deployments repository for examples on how to set up these tools.