What is Phoenix?

Phoenix — is a web framework built with the Elixir functional programming language. In turn, Elixir is based on Erlang, which uses a BEAM virtual machine and OTP(Open Telecom Platform). Phoenix is used for building fault-tolerant, low-latency, distributed real-time web applications.

Installation Phoenix

The best official installation guide.

Local development in Docker with hot-reload

Add a Dockerfile

1. Create a file named Dockerfile based on elixir image, thus helping to avoid the installation of development environments for Elixir and Erlang

FROM elixir:latest

WORKDIR — set working directory

WORKDIR /app

Import the necessary files into the working directory

ADD . /app

Update the image and install the following packages:

• npm - needed to manage js dependencies
• build-essential - meta-packages required for compiling
• inotify-tools - Phoenix provides a very handy feature called Live Reloading. As you change your views or your assets, it automatically reloads the page in the browser. In order for this functionality to work, you need a (filesystem watcher)[https://github.com/inotify-tools/inotify-tools/wiki].

RUN apt-get update && apt-get -y install npm build-essential inotify-tools

Install js dependencies inside the assets directory

RUN npm install --prefix ./assets

Install local copies of hex and rebar

• hex - the package manager for the Erlang ecosystem
• rebar - build tool and package management tool for Erlang
• --force - forces installation without a shell prompt; primarily intended for automation in build systems like make

RUN mix local.hex --force && mix local.rebar --force

Install dependencies and compile

RUN mix do deps.get, compile

Expose port 4000

EXPOSE 4000

Run a bash-script at the root of the project

CMD ["./dev"]

Finally Dockerfile file

FROM elixir:latest

WORKDIR /app

ADD . /app

RUN apt-get update && apt-get -y install npm build-essential inotify-tools
RUN npm install --prefix ./assets
RUN mix local.hex --force && mix local.rebar --force
RUN mix do deps.get, compile

EXPOSE 4000

CMD ["./dev"]

Add a bash script to run the project

Once the project is compiled, you can start an iex session inside the project by running the command below. The -S mix is necessary to load the project in the interactive shell:

#!/bin/sh
exec iex -S mix phx.server

Add a docker-compose.yml

version: "3.9" # use the latest version
services:
  phoenix-app:
    container_name: phoenix-container
    restart: always

    build: . # specify the path to the Dockerfile, in our case it is in the root of the project

    environment:
      - MIX_ENV=dev # set mix environment

    # mount the necessary files that will respond to changes in the code. Required for hot reloading
    volumes:
      - ./assets:/app/assets
      - ./priv:/app/priv
      - ./lib:/app/lib
      - ./config:/app/config
    ports:
      - "4000:4000"

    # `tty: true` и `stdin_open: true` required to interactive shell. Otherwise, iex will throw an error
    tty: true
    stdin_open: true

Conclusions

This article shows how to develop Phoenix projects in a Docker environment with hot reload in practice.