Svelix

Example app with Phoenix, Inertia.js, and Svelte 5

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Svelix

An example repo for a modern monolith using Phoenix, Inertia.js, and Svelte 5. You can find the application running at https://svelix.skyturtle.io/

It is deployed to a self-hosted VPS using Coolify. A healthcheck has been enabled using a custom plug module, SvelixWeb.Healthcheck.

On the home page you will see a basic navbar with three links: Home, Counter, and Stock. Home and Counter are Svelte components and can be found within the assets directory. The Home page receives props (text in the h1 tag and the name Turtle) from a standard Phoenix controller. The navigation for the links between these pages uses Inertia with the use:inertia Svelte directive. Stock is the default home page that ships with mix phx.new my_app.

Development

Svelte requires an esbuild plugin so you need to have Node.js installed. This application was built using Node.js v22.13.1. Aside from that, it will have the same requirements as any other Phoenix app e.g., Postgres, Elixir, etc.

To start your Phoenix server:

Run mix setup to install and setup dependencies
Start Phoenix endpoint with mix phx.server or inside IEx with iex -S mix phx.server

Now you can visit localhost:4000 from your browser. The home page is a Svelte component being rendered by Inertia.

Inertia.js Setup

The official setup instructions can be found on HexDocs for the Inertia.js Phoenix Adapter. These setup instructions give a high-level overview of the steps. The details below are to help out my future self and also clariy some questions I had as I was going through the instructions. The server-side setup follows the official instructions closely. The client-side setup is fairly different because the Phoenix adapter docs use React.

Server-side Setup

Add the :inertia package to your deps in mix.exs and run mix deps.get

  {:inertia, "~> 2.2.0"}

Add Inertia configuration to confix.exs
Add Inertia helpers for Controller and HTML to SvelixWeb
Add Inertia.Plug to your browser pipeline in your router.ex
Update <head> component in the root layout so the client-side library will keep the title in sync

Client-side Setup

NOTE: SSR IS NOT WORKING YET EVEN THOUGH THE CODE IS IN build.js

Install the Inertia.js library for your frontend library as well as the frontend library itself. Remember, everything "frontend" related will be done in the assets directory. Also, because Svelte will be processed through an esbuild plugin, we will install those required dependencies and also remove the esbuild hex package from the Elixir deps.

We are using --prefix assets so that these commands can be run from the project's root directory.

Install the esbuild and the esbuild-svelte plugin:

npm --prefix assets install -D esbuild esbuild-svelte

Install the inertiajs client-side library and other libraries already included in stock Phoenix app.

npm --prefix assets install \
@inertiajs/svelte topbar axios \
./deps/phoenix ./deps/phoenix_html ./deps/phoenix_live_view

Initialize the client-side library in app.js.
Add ssr.js
Remove ESBuild (to prepare to use custom build.js)
Delete config :esbuild from config.exs
Remove esbuild dependency in mix.exs
Unlock esbuild dependency
mix deps.unlock esbuild
Add custom esbuild script, build.js
Replace esbuild watchers to use custom build.js script
Add a page component in assets/js/pages/ to render. Otherwise you're going to get an error like:

[WARNING] The glob pattern import("./pages/**/*.svelte") did not match any files [empty-glob]

    js/app.js:62:24:
      62 │     return await import(`./pages/${name}.svelte`);
         ╵                         ~~~~~~~~~~~~~~~~~~~~~~~~

Update aliases in mix.exs
Add priv/ssr.js to gitignore
Add Inertia.SSR to supervision tree in application.ex
Add SSR to Inertia :config -> enable true

Deploying to Coolify

TODO: Explain building release, adding Node.js to Dockerfile that is created when building a release, some pain points: forgot to add Node.js to builder, ran npm install --omit=dev (which causes mix assets.deploy to fail because esbuild is a dev dependency), Ecto migrations (had to change the last command in Dockerfile to run migations before starting the app)

Add health checks. This article explains how to set up a Plug for health checks: Health checks for Plug and Phoenix.

For Coolify, under Healthcheck, check the box for "Enabled". For the settings:

Method GET, Scheme http, Host localhost, Port leave blank (placeholder is 80), Path /health-check (which is the route set up in SvelixWeb.Healthcheck)

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