CI workflows on Tangled for Elixir

Tangled is a Github competitor built on top of atproto. The company behind it is a Finnish startup, situated in Finland, with all servers and data held in the EU. They have taken VC money, but at least conceptually the fact that it's built on top of atproto means that if the strings that came with that cash pull the company in the wrong direction, your data is still yours and you could potentially move it somewhere else.

Continuing down my atproto rabbit hole, I spent some time getting a CI workflow set up for https://tangled.org/jola.dev/annot.at. I couldn’t find any examples of Elixir CI workflows for Tangled so it took some experimenting.

This uses the new microvm engine that was only recently released, which enables us to run a PostgreSQL service in the workflow. By default it only listens on a unix socket, so we have to set some extra configuration there for it to match the standard Phoenix scaffold setup.

when:
  - event: ["push", "pull_request"]
    branch: ["main"]

engine: microvm
image: nixos

dependencies:
  - beam29Packages.elixir_1_20
  - beam29Packages.erlang

services:
  postgresql:
    enable: true
    enableTCPIP: true
    authentication: |
      host all all 127.0.0.1/32 trust
      host all all ::1/128 trust

steps:
  - name: setup
    command: |
      mix local.hex --force
      mix local.rebar --force
      mix deps.get
  - name: compile
    command: mix compile --warnings-as-errors
  - name: format
    command: mix format --check-formatted
  - name: credo
    command: mix credo --strict
  - name: test
    command: mix test --warnings-as-errors
  - name: unused
    command: mix deps.unlock --check-unused

The trickiest part was using specific versions of Elixir and Erlang. You can use

dependencies:
  - elixir
  - erlang

but that gives you an unspecified version of Elixir. It happened to be 1.18 when I tried. Instead, you'll want to find specific NixOS packages to depend on, like the full workflow does.

dependencies:
  - beam29Packages.elixir_1_20
  - beam29Packages.erlang

The BEAM 29 packages I found here https://mynixos.com/nixpkgs/packages/beam29Packages. This still doesn't give me an exact version, but it was close enough for me.

I don’t have much experience with NixOS so it was a bit of trial and error to get here, but once I got the config right it runs perfect. Here’s an example run https://tangled.org/jola.dev/annot.at/pipelines/28076/workflow/ci.yml.

Now to go figure out how to self-host a knot and a spindle. Don’t have to do that, you can use the servers Tangled offer, but I figure it’s more fun this way.