Elixir Phoenix Nix demo

This repo contains basic Phoenix application and nix code required to be able to run the app locally and build docker image for a docker-based deployment.

I strongly suggest to use nix-direnv for a bit nicer development UX.

Structure:

./demo_phx - main app generated with mix phx.new demo_phx --live
./nix - nix code required to set everything up
./bin - additional scripts to run postgres (installed via Nix too) and build docker image

Nix

This repo uses Nix flakes.

Docker images building is currently skipped for MacOS, everything else should work.

There's a lot of boilerplate in flake.nix, the 'meat' is in ./nix.

Phoenix app

There are only 3 changes vs what's generated.

First one is related to esbuild, I wanted to avoid any repeated downloads when building docker image so there's additional env variable pointing to esbuild. The tool itself is downloaded via nix.

config/config.exs

config :esbuild,
  version: "0.12.18",
+ path: System.get_env("ESBUILD_PATH"),
  default: [
    args:
      ~w(js/app.js --bundle --target=es2016 --outdir=../priv/static/assets --external:/fonts/* --external:/images/*),
    cd: Path.expand("../assets", __DIR__),
-   env: %{"NODE_PATH" => Path.expand("../deps", __DIR__)}
+   env: %{"NODE_PATH" => Path.expand(System.get_env("MIX_DEPS_PATH", "../deps"), __DIR__)}
  ]

Second change visible above is related to location of dependencies, during docker image build they're in a different location (nix store), so without this change esbuild wouldn't be able to resolve Phoenix JS libraries.

Third change is unique to my set up and might be skipped, it's a binding to IPv4 instead to IPv6 in config/runtime.exs.

Why have I done this?

I wanted to learn a bit of Nix and see for myself how hard it would be to use Nix to manage both local and docker based production build without a lot of duplication.

Running

$ ls -a
.envrc  .git  .gitignore  bin  demo_phx  flake.lock  flake.nix  nix  README.md
$ nix develop
$ ls -a
.envrc  .git  .gitignore  .nix-hex  .nix-mix  bin  demo_phx  flake.lock  flake.nix  nix  README.md

Basic directories are automatically created and now you have required dependencies in $PATH

Let's create db and run tests

$ db-run
$ cd demo_phx
$ mix test

Finished in 0.03 seconds (0.03s async, 0.00s sync)
3 tests, 0 failures

Everything should pass successfully.

Docker image

# building
$ bin/ci-image
# running
$ docker run --rm -e DATABASE_URL="$DATABASE_URL" -e SECRET_KEY_BASE="AAS+PPF6mkBp1" --network host phx-nix:latest

In the command above, you'll notice network mode host is used, this is because it connects to postgres instance running locally.

TODO

GitHub Actions CI
MacOS tests, including M1
Additional checks inside flake.nix

If you have any suggestions how to simplify code here - please open an issue or send me an email.

arathunku / phx-nix-example