Debugging a Rails app running in Docker containers using VSCode

Simple Rails in Docker

To get a simple vanilla Rails app up and running in a Docker container on your local machine follow these instructions

Debuging with Visual Studio Code

The Ruby on Rails debugging in VS Code recipe on GitHub is about debuging on your local machine, not in Docker containers, but the Bonus content goes on to cover Docker. This bonus content details the following.

The configuration to add to your .vscode/launch.json file

Add a configuration like this:

{
    "name": "Rails Debug",
    "type": "Ruby",
    "request": "attach",
    "cwd": "${workspaceRoot}",
    "remoteWorkspaceRoot": "/app",
    "remoteHost": "0.0.0.0",
    "remotePort": "1234",
    "showDebuggerOutput": true
}

The matching changes to your docker-compose.yml and Dockerfile files

The port number in your .vscode/launch.json file will need to match the one specified in your docker-compose.yml file. You will also need to make rails available for debugging and the Dockerfile needs to expose the same ports.

Between your docker-compose.yml and Dockerfile files you need to run the Rails server from rdebug-ide. For example:

Included in a docker-compose.yml file

app:
  build: .
  volumes:
    - .:/app
  ports:
    - "1234:1234"
    - "3000:3000"
    - "26162:26162"
  depends_on:
    - db
  environment:
    - POSTGRES_USER
    - POSTGRES_PASSWORD
    - RDEBUG_IDE

Included in a Dockerfile

EXPOSE 3000
EXPOSE 1234
EXPOSE 26162

COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]

Included in the an entrypoint.sh file

HOST=0.0.0.0
PORT=3000
DEBUG_PORT=1234
DISPATCHER_PORT=26162

if [ ${RDEBUG_IDE:-0} -eq 1 ]
then
    echo "Starting rails server under rdebug-ide"
    rdebug-ide --skip_wait_for_start --host $HOST --port $DEBUG_PORT --dispatcher-port $DISPATCHER_PORT -- ./bin/rails server --binding $HOST --port $PORT
else
    echo "Starting rails server without rdebug-ide"
    rails server --binding $HOST --port $PORT
fi

At that point you can set RDEBUG_IDE to 1 in your .env file (based on .env.example), run the container with docker compose up, and connect to the container in VSCode, setting breakpoints etc.

dumbledad/rails-vscode-docker