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Elixir Phoenix Applications: Deploy to Heroku

Recently, I ended up deploying a small Phoenix application on Heroku. Coming from Rails, I ran into a few hiccups and this post is my attempt to document those.

elixir basics

Step 1: Configure Your Database

If you want to deploy to Heroku, the first step is to configure your database URL. Log in to Heroku to take the DATABASE_URL environment variable and add it to your prod.exs file.

In config/prod.exs:

Step 2: Generate and configure a secret key

Generate a secret key with this phoenix command:

Set an ENV variable on your Heroku server to store the secret key. In the example below, I set an ENV variable called SECRET_KEY_BASE on my Heroku server.

Step 3: Set up your other ENV variables

Specify a POOL_SIZE of 10 or less if you’re running on the free Heroku plan.

In my particular use case, I needed to connect to the YouTube API with an API key provided by Google. When I wanted to be able to connect to the API locally, I created a .env file.

To make it work, I had to issue a source .env every time I opened a new terminal window and ran my Phoenix application locally.

Step 4: Configure your buildpacks

You’ll need to configure an elixir buildpack.

To run iex -S mix on Heroku, set config_vars_to_export. Without this, you will get errors when you run iex -S mix on Heroku.


If you follow these steps in addition to the Phoenix documentation, you will be able to successfully deploy your phoenix application on Heroku.

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