06-docker-compose

Docker Compose

Docker Compose is a tool used to configure and run applications consisting of multiple containers. With compose you can run multiple cooperating contianers with only a single command, that builds your containers and sorrunding environment based on the configurations described in a docker-compose.yaml file.

It is in essence two parts to it. The first beeing the docker compose file's standard for defining the commandline flags of docker run, for multiple containers. The second is the tool that runs the containers with the configuration defiend in the file.

YAML-configuration

A docker-compose file often consist of multuple services. Think of a service as an application or a container. In the example below you can see some of the fiels one may configure:

services:
  backend:
    container_name: backend
    build: ./backend
    restart: always
    ports:
      - 8000:8000
    environment:
      - DATABASE_HOST=database:5432
    network:
      - web
    volumes: ./backend/cache:/app/cache/

The container name is backend. It has no image defined, but is rather build from the dockerfile within the ./backend directory. It is configured to restart if were to stop. The other keys should be known from previous sections. In short, the port 8000 is forwarded to the container, and it is part of the network web. Additionally, a volume is mounted so that the cache is kept even though the container is restarted.

Usage

Depending on how it is installed, use either docker-compose or docker compose to run the cli tool. The most basic commands are:

docker compose up -d --build
docker compose down

up brings up all the services configured in the dockerfile and outputs the logs for all of them. As with docker run, -d may be specified to run it detached (in the background). If using build, it is also wise to use --build to force the images to be rebuilt before the container starts. Otherwise, changes to source files may not be reflected in the new container.

down stops all the containers, just like docker stop.

Trial run

📝 Run the following to start the containers defined in docker-compose.yml:

docker compose up -d

The containers are now running as if you started them manually with docker run.

📝 See whats going on with docker ps and docker compose logs.

One container name will be automatically deduced from the folder and container id, as container_name was not specified.

📝 To stop all the containers run the following:

docker compose down

Tasks

In this session we will build a realworld application consisting of the following:

• Frontend written in React Redux
• Backend written in Node
• Mysql database

Prerequisites

In the 06-docker-compose/realworld folder, clone the following react frontend khaledosman/react-redux-realworld-example-app and node backendditsmod/realworld:

git clone [email protected]:khaledosman/react-redux-realworld-example-app.git realworld-frontend

git clone [email protected]:ditsmod/realworld.git realworld-backend

📝 Both the frontend and backend are missing Dockerfiles, so you will have to create these yourself, one inside the frontend folder and another in the backend.

NOTE: Some dependency issues might occur in the frontend, so try using --force when installing dependencies with npm.

Task 1

Change directory to 06-docker-compose/realworld:

cd 06-docker-compose/realworld

Take a look at the docker-compose.yml file and run the following command:

docker compose up -d --build

List the running containers with the docker ps command and see that a frontend application is running with the port 4100 exposed.

Task 2

When opening the browser at localhost:4100 we see that the frontend application is running and it is using the production backend api. Lets run the backend in a container instead.

We have already cloned the backend project in 06-docker-compose/realworld/backend/node-realworld. Follow the same structure as the one describing the frontend-service and include these instructions:

container_name:
image:
build:
ports:
environment:
  - NODE_OPTIONS="--max-old-space-size=4096"

Run the following command again:

docker compose up -d --build

See that all containers are running with the docker ps command.

Task 3

Now try to access the appliaction through localhost:4100 again.

Woops. No connection?? Try adding an environment variable that defines the backend-service with its port as the value.

environment:
  - REACT_APP_BACKEND_URL=[backend-service:port]

Add this to the spec of the conduit-frontend service in the docker-compose.yml file and run the same docker-compose command as above.

Task 4

Now localhost:4100 should show the same interface as the first time you built the docker-compose file. But something is missing...

There are noe tags and no posts showing. We need to add a database for this.

Add another service to your docker-compose.yml file:

real_world:
  container_name: database
  image: mysql:latest
  ports:
    - "3306:3306"
  volumes:
    - ./realworld-backend/packages/server/sql/dump:/docker-entrypoint-initdb.d/
  environment:
    - MYSQL_ALLOW_EMPTY_PASSWORD=true
    - MYSQL_DATABASE=realworld