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Awesome Open Source

Dockerized Elixir/Phoenix Development Environment

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I have been working on a long-running personal Phoenix project since Phoenix 1.0.2. Over the past year and a half or so, Phoenix and Elixir have undergone numerous changes, and some of them (okay most of them) broke my application code. Things really went south after I found myself working on multiple different projects that were built on different Phoenix versions. This reminded me a lot of the early Ruby and Rails days (and fighting rbenv and bundle).

This project was conceived to deal with the issues of running different Elixir and Phoenix versions and supporting the development of apps built with different Elixir and Phoenix versions.

New: Support for VS Code Remote Extension

After cloning this repository, open the folder in Visual Studio Code's Remote Extension to get a full Development Environment (with PostgreSQL Database) spun up automatically.

See for more details.

Getting Started

It's so simple: just clone this repository.

You can specify a particular Phoenix version by targeting the corresponding release tag of this repository.

For instance, for a dockerized development environment for Phoenix 1.6.0 you could run:

git clone -b 1.6.0 ~/Projects/hello-phoenix

New with Elixir 1.9: Releases

Follow this Github Gist to prepare a minimal Docker release image based on Alpine Linux (about 38MB for a Phoenix Webapp).

New Application from Scratch

Navigate the to where you cloned this repository, for example:

cd ~/Projects/hello-phoenix

Initialize a new phoenix application. The following command will create a new Phoenix application called hello under the src/ directory, which is mounted inside the container under /app (the default work dir).

./mix . --app hello

Why does this work? The docker-compose.yml file specifies that your local src/ directory is mapped inside the docker container as /app. And /app in the container is marked as the working directory for any command that is being executed, such as mix

NOTE: It is important to specify your app name through the --app <name> option, as Phoenix will otherwise name your app from the target directory passed in, which in our case is .

NOTE: It is okay to answer Y when phoenix states that the /app directory already exists.

NOTE: Starting from 1.3.0 the mix command has been deprecated. You will have to use the command instead of or mix deps.get will fail!

Alternative: Existing Application

Copy your existing code Phoenix application code to the src/ directory in the cloned repository.

NOTE: the src/ directory won't exist so you'll have to create it first.



The docker-compose.yml file defines a database service container named db running a PostgreSQL database that is available to the main application container via the hostname db. By default Phoenix assumes that you are running a database locally.

Modify the Ecto configuration src/config/dev.exs to point to the DB container:

# Configure your database
config :test, Test.Repo,
  adapter: Ecto.Adapters.Postgres,
  username: "postgres",
  password: "postgres",
  database: "test_dev",
  hostname: "db",
  pool_size: 10

Initialize the Database with Ecto

When you first start out, the db container will have no databases. Let's initialize a development DB using Ecto:

./mix ecto.create

If you copied an existing application, now would be the time to run your database migrations.

./mix ecto.migrate

Starting the Application

Starting your application is incredibly easy, you can either run:

docker-compose up


./mix phx.server

Once up, it will be available under http://localhost:4000.

You may need to update config/dev.exs and set the endpoint listen address to like so:

config :hello_world, HelloWorldWeb.Endpoint,
  # Binding to loopback ipv4 address prevents access from other machines.
  # Change to `ip: {0, 0, 0, 0}` to allow access from other machines.
  http: [ip: {0, 0, 0, 0}, port: 4000],
  check_origin: false,
  code_reloader: true,
  debug_errors: true,
  secret_key_base: "rM/QJOrRiW+3WWLw+lHJ8kUFJK/LTrwakSG/ftGYl8jYN0FKqfgS50l2C9BdKMoK",
  watchers: [
    # Start the esbuild watcher by calling Esbuild.install_and_run(:default, args)
    esbuild: {Esbuild, :install_and_run, [:default, ~w(--sourcemap=inline --watch)]}


Executing custom commands

To run commands other than mix tasks, you can use the ./run script.

./run iex -S mix

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