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Deploy a Phoenix App on Render

This guide walks through deploying a Phoenix application on Render.

The finished code for this example is available on GitHub.

Getting started

Create a new Phoenix app in the terminal. We don’t need a database for this example, so pass the --no-ecto flag to mix:

mix archive.install hex phx_new
mix phx.new phoenix_hello --no-ecto # also fetch and install dependencies
cd phoenix_hello

Create a build script

We need to run a series of commands to build our app on every push to our Git repo, which we can accomplish with a build script. Create a script named build.sh at the root of your repo:

#!/usr/bin/env bash
# exit on error
set -o errexit

# Initial setup
mix deps.get --only prod
MIX_ENV=prod mix compile

# Compile assets
# Make sure tailwind and esbuild are installed
MIX_ENV=prod mix assets.build
# Build minified assets
MIX_ENV=prod mix assets.deploy

# Create server script, Build the release, and overwrite the existing release directory
MIX_ENV=prod mix phx.gen.release
MIX_ENV=prod mix release --overwrite

Make sure the script is executable before you commit it:

chmod a+x build.sh

Update your app for Render

Update config/runtime.exs to change the highlighted line below:

host = System.get_env("PHX_HOST") || "example.com"port = String.to_integer(System.get_env("PORT") || "4000")

to this:

host = System.get_env("RENDER_EXTERNAL_HOSTNAME") || "localhost"port = String.to_integer(System.get_env("PORT") || "4000")

Render populates RENDER_EXTERNAL_HOSTNAME for config/runtime.exs.

If you add a custom domain to your Render app, don’t forget to change the host to your new domain.

Build and test your release locally

Compile your release locally by running ./build.sh. The end of the output should look like this:

./build.sh

* assembling phoenix_hello-0.1.0 on MIX_ENV=prod
* using config/runtime.exs to configure the release at runtime
* skipping elixir.bat for windows (bin/elixir.bat not found in the Elixir installation)
* skipping iex.bat for windows (bin/iex.bat not found in the Elixir installation)

Release created at _build/prod/rel/phoenix_hello

    # To start your system
    _build/prod/rel/phoenix_hello/bin/phoenix_hello start

Once the release is running:

    # To connect to it remotely
    _build/prod/rel/phoenix_hello/bin/phoenix_hello remote

    # To stop it gracefully (you may also send SIGINT/SIGTERM)
    _build/prod/rel/phoenix_hello/bin/phoenix_hello stop

To list all commands:

    _build/prod/rel/phoenix_hello/bin/phoenix_hello

Test your release by running the following command and navigating to http://localhost:4000.

SECRET_KEY_BASE=`mix phx.gen.secret` _build/prod/rel/phoenix_hello/bin/server

You might need to run mix deps.get locally to enable phx.gen.secret, because it’s a dev dependency instead of a prod dependency. You should add/commit your mix.lock file before running this.

You might notice the start command is different from the output of build.sh. The phx.gen.release command in the build script creates a wrapper for launching your application that include setting the PHX_SERVER variable, so a webserver will start. You can also use the start command from the build.sh output, but you will need to set PHX_SERVER to true in the environment variables if you do.

If everything looks good, push your changes to your repo. Next, let’s deploy your app to Render!

Deploy to Render

  1. In the Render Dashboard, create a new web service and connect your Phoenix app’s repo.

  2. Set the following values during service creation:

    SettingValue
    RuntimeElixir
    Build Command./build.sh
    Start Command_build/prod/rel/phoenix_hello/bin/server

  3. Add the following environment variable to your web service:

    KeyValue
    SECRET_KEY_BASEA sufficiently strong secret. Generate it locally by running mix phx.gen.secret

That’s it! Your Phoenix web service will be live at its onrender.com subdomain as soon as the deploy finishes.

Read about customizing Elixir and Erlang/OTP versions for your app.