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:

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:

Make sure the script is executable before you commit it:

Update your app for Render

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

to this:

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:

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

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:

   Setting	Value
   Language	Elixir
   Build Command	./build.sh
   Start Command	_build/prod/rel/phoenix_hello/bin/server

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

   Key	Value
   SECRET_KEY_BASE	A 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.