Buildbot-nix is a NixOS module designed to integrate Buildbot, a continuous integration (CI) framework, into the Nix ecosystem. This module is under active development, and while it's generally stable and widely used, please be aware that some APIs may change over time.

• Fast, Parallel evaluation using nix-eval-jobs
• Gitea/Github integration:
  • Login with GitHub to control builds
  • CI status notification in pull requests and on the default branch
• All builds share the same nix store for speed
• The last attribute of a build is protected from garbage collection
• Build matrix based on .#checks attributes
• No arbitrary code runs outside of the Nix sandbox
• experimental hercules-ci effect to run impure CI steps i.e. deploying NixOS

To set up Buildbot using Buildbot-nix, you can start by exploring the provided examples:

• Check out the basic setup in example.
• Learn about configuring the Buildbot master in master module.
• Understand how to set up a Buildbot worker in worker module.
• For local development, see Local Development Guide.

Additionally, you can find real-world examples at the end of this document.

Buildbot masters and workers can be deployed either on the same machine or on separate machines. To support multiple architectures, configure them as nix remote builders. For a practical NixOS example, see this remote builder configuration.

The module applies custom patches that only apply to buildbot > 4.0.0. To use buildbot-nix with NixOS 24.05, you should therefore not override the nixpkgs input to your own stable version of buildbot-nix and leave it to the default instead that is set to nixos-unstable-small.

So instead of using this in your flake

inputs = {
  buildbot-nix.url = "github:nix-community/buildbot-nix";
  buildbot-nix.inputs.nixpkgs.follows = "nixpkgs";
};

Just use:

inputs = {
  buildbot-nix.url = "github:nix-community/buildbot-nix";
};

An alternative is to point nixpkgs to your own version of nixpkgs-unstable in case you are already using it elsewhere.

Buildbot-nix automatically triggers builds for your project under these conditions:

• When a pull request is opened.
• When a commit is pushed to the default git branch.

It does this by evaluating the .#checks attribute of your project's flake in parallel. Each attribute found results in a separate build step. You can test these builds locally using nix flake check -L or nix-fast-build.

If you need to build other parts of your flake, such as packages or NixOS machines, you should re-export these into the .#checks output. Here are two examples to guide you:

• Using flake-parts.
• A plain flake example.

At the moment buildbot-nix offers two access modes, public and fullyPrivate. public is the default and gives read-only access to all of buildbot, including builds, logs and builders. For read-write access, authentication is still needed, this is controlled by the authBackend option.

fullyPrivate will hide buildbot behind oauth2-proxy which protects the whole buildbot instance. buildbot fetches the currently authenticated user from oauth2-proxy so the same admin, organisation rules apply.

fullyPrivate acccess mode is a workaround as buildbot does not support hiding information natively as now.

For some actions a login is required. The authentication backend is set by the services.buildbot-nix.master.authBackend NixOS option ("github", "gitea", "oidc", or others).

Note: You can configure both GitHub and Gitea integrations simultaneously, regardless of which authentication backend you choose. The auth backend only determines how users log in to the Buildbot interface.

We have the following two roles:

• Admins:
  • The list of admin usernames is hard-coded in the NixOS configuration.
  • admins can reload the project list
• Organisation member:
  • All member of the organisation where this repository is located
  • They can restart builds

Buildbot-nix uses GitHub App authentication to integrate with GitHub repositories. This enables automatic webhook setup, commit status updates, and secure authentication.

See the GitHub documentation for setup instructions.

Buildbot-nix integrates with Gitea using access tokens for repository management and OAuth2 for user authentication. This enables automatic webhook setup, commit status updates, and secure authentication.

See the Gitea documentation for setup instructions.

Buildbot-nix supports generic OpenID Connect (OIDC) authentication, allowing you to use any OIDC-compliant identity provider (Keycloak, PocketID, Authentik, etc.) for user login.

See the OIDC documentation for configuration details.

To enable fully private mode, set acessMode.fullyPrivate to an attrset containing the required options for fully private use, refer to the examples and module implementation (nix/master.nix).

This access mode honors the admins option in addition to the accessMode.fullyPrivate.organisations option. To allow access from certain organisations, you must explicitly list them.

If you've set authBackend previously, unset it, or you will get an error about a conflicting definitions. fullyPrivate requires the authBackend to be set to basichttpauth to function (this is handled by the module, which is why you can leave it unset). For a concrete example please refer to fully-private-github

Currently buildbot-nix will look for a file named buildbot-nix.toml in the root of whichever branch it's currently evaluating, parse it as TOML and apply the configuration specified. The following table illustrates the supported options.

To access the build results on other machines there are two options at the moment

You can set up a binary cache on your buildbot-worker machine to make its nix store accessible from other machines. Check out the README of the project, for an example configuration

Buildbot-nix also supports pushing packages to cachix. Check out the comment out example configuration in our repository.

Buildbot-nix does not have native support for pushing packages to attic yet. However it's possible to integrate run a systemd service as described in this example configuration. The systemd service watches for changes in the local buildbot-nix store and uploads the contents to the attic cache.

See flake.nix for an example and [https://docs.hercules-ci.com/hercules-ci/effects/] for documentation.

You can run hercules-effects locally using the buildbot-effects cli:

$ buildbot-effects --help
usage: buildbot-effects [-h] [--secrets SECRETS] [--rev REV] [--branch BRANCH] [--repo REPO] [--path PATH] {list,run,run-all} ...

Run effects from a hercules-ci flake

positional arguments:
  {list,run,run-all}  Command to run
    list              List available effects
    run               Run an effect
    run-all           Run all effects

options:
  -h, --help          show this help message and exit
  --secrets SECRETS   Path to a json file with secrets
  --rev REV           Git revision to use
  --branch BRANCH     Git branch to use
  --repo REPO         Git repo to prepend to be
  --path PATH         Path to the repository

Example from the buildbot-nix repository:

$ git clone github.com/nix-community/buildbot-nix
$ cd buildbot-nix

$ nix run github:nix-community/buildbot-nix#buildbot-effects -- list
[
  "deploy"
]

$ nix run github:nix-community/buildbot-nix#buildbot-effects -- --branch main run deploy
{branch:main,rev:5d2e0af1cfccfc209b893b89392cf80f5640d936,tag:null}
Hello, world!

The lix overlay overrides nix-eval-jobs with a version that doesn't work with buildbot-nix because of missing features and therefore cannot be used together with the buildbot-nix module.

Possible workaround: Don't use the overlay and only set the nix.package = pkgs.lix; NixOS option.

See Buildbot-nix in action in these deployments:

The following instances run on GitHub:

• Nix-community infra: Configuration | Instance
• Mic92's dotfiles: Configuration | Instance
• Technical University Munich: Configuration | Instance
• Numtide: Instance
• Ngi0: Instance

The following instances integrated with Gitea:

• Clan infra: Configuration | Instance

We have a matrix channel at buildbot-nix.

For commercial support, please contact Mic92 at joerg@thalheim.io or reach out to Numtide.