Elixir (Phoenix) Nix Example

Example repo to show off how I use Nix as build environment for Elixir / Phoenix projects.
Important Nix stuff is located within flake.nix / default.nix & pkg/ folder.
This repo is not a working project! It just contains parts of the workflow.

Note

Since starting this example a lot of positive things have happened or are happening within Nixpkgs. You may be interested in mixRelease or friends.

I for myself stopped to use a full Nix leveraging build setup. I only use parts of this workflow anymore with reusing local _build & deps as it speeds up things for my requirements enorm.

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Setup

This repo provides an easy environment setup by the usage of Nix (w/ flakes enabled).
Nix currently runs on Linux and macOS.

• Getting Nix

Enabling Nix flakes (Nix v2.4)

# ~/.config/nix/nix.conf
experimental-features = nix-command flakes

By using Nix, beside Nix nothing else needs to be installed manually.

Windows
Recommended also using Nix within a Linux Virtual Machine or WSL 2.

Manual Setup

For maintaining simplicity, instructions for a manual setup isn't part of this readme.
Anyway, required dependencies:

• Elixir (& Erlang)
• PostgreSQL
• (Node.js)

Development

Environment

# Enter shell w/ development environment + temporary PostgreSQL database
nix develop

# Run commands without shell
nix develop --command <command>

Basics commands for working with Elixir / Phoenix

# Get Elixir mix deps
mix deps.get

# Get JS packages
npm install --prefix assets

# Start Phoenix server
mix phx.server

# Start Elixir application
mix run --no-halt

# Enter IEx
iex -S mix

# Run tests
mix test

Build

# mix deps
nix build --file default.nix mix_deps --relaxed-sandbox

# JS packages
nix build --file default.nix node_modules --relaxed-sandbox

# Compile
nix build --file default.nix mix_build --relaxed-sandbox

# Compile cacheable `_build`
nix develop --command mix compile

# Generate docs using `mix docs`
nix build --file default.nix docs --relaxed-sandbox

# Build production release using `mix release`
nix build --file default.nix release --relaxed-sandbox

Maintenance

# Update pinned Nix pkgs
elixir pkg/scripts/pkgs_update.exs
# Update flake.lock
nix flake update

# Check / update / clean Mix deps
mix hex.outdated
mix deps.update --all
mix deps.clean --unlock --unused

# Check / update / clean NPM packages
npm outdated --prefix assets
npm update --prefix assets
npm prune --prefix assets

# Flake checks
nix flake check

direnv

direnv let's you automatically load environment variables per directory defined in .envrc.

Working with direnv

# Install via Nix
nix profile install nixpkgs#direnv

# Setup hook
# Add the following to your .profile
eval "$(direnv hook bash)"