Docker Compose

Till now we’ve spent all our time exploring the single-container Docker client. In the Docker ecosystem, however, there are powerful orchestration tools which play very nicely with Docker:

1. Docker Compose — A tool for defining and running multi-container Docker applications.
2. Kubernetes — An open-source system for automating deployment, scaling, and management of containerized applications.
3. Docker Swarm — Native clustering for Docker.

In this section, we are going to look at Docker Compose, and see how it can make dealing with multi-container apps easy.

What is Docker Compose?

Compose is a tool that is used for defining and running multi-container Docker apps. It uses a YAML configuration file called docker-compose.yml to configure your application’s services. Then, with a single command, you create and start all the services from your configuration. Compose works in all environments: production, staging, development, testing, as well as CI workflows.

Let’s see how we can create a docker-compose.yml file for our SF-Foodtrucks app and evaluate whether Docker Compose lives up to its promise.

Installation

If you are using Docker Desktop (Mac, Windows, or Linux), Docker Compose V2 is already included out of the box as a subcommand plugin (docker compose).

You can verify your installation by checking the version:

$ docker compose version
Docker Compose version v2.27.0

Note on V1 vs V2: Earlier versions of Docker Compose used a separate hyphenated command (docker-compose). Docker officially retired V1 in 2023. Today, Compose is invoked directly via docker compose with a space.

The docker-compose.yml File

Now that we have Docker Compose ready, let’s look at the docker-compose.yml file:

services:
  es:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.17.18
    container_name: es
    environment:
      - discovery.type=single-node
    ports:
      - 9200:9200
    volumes:
      - esdata1:/usr/share/elasticsearch/data
  web:
    image: prakhar1989/foodtrucks-web
    command: python3 app.py
    depends_on:
      - es
    ports:
      - 5000:5000
    volumes:
      - ./flask-app:/opt/flask-app
volumes:
  esdata1:
    driver: local

Let’s breakdown what this file means:

• At the top level, under services:, we define the names of our services: es and web.
• For each service, image specifies the Docker image to use. For es, we use the official Elasticsearch image. For web, we use our Flask app image.
• ports maps container ports to host ports.
• depends_on tells Docker to start the es container before starting web.
• volumes defines persistent data mounts so data survives container restarts.

Note: The top-level version: "3" schema attribute used in older tutorials is now deprecated in the modern Compose Specification and can be safely omitted.

Running Docker Compose

Make sure any existing standalone containers are stopped before launching:

$ docker stop es foodtrucks-web
$ docker rm es foodtrucks-web

Now, navigate to the directory containing your docker-compose.yml file and run:

$ docker compose up
[+] Running 3/3
 ✔ Network foodtrucks_default  Created
 ✔ Container es                Created
 ✔ Container foodtrucks-web-1  Created
Attaching to es, foodtrucks-web-1

Head over to http://localhost:5000 to see your app live! With just one command, Docker Compose created a private network (foodtrucks_default), initialized both containers, attached their logging outputs, and wired up DNS service discovery between them.

To run the services in the background (detached mode):

$ docker compose up -d
[+] Running 2/2
 ✔ Container es                Started
 ✔ Container foodtrucks-web-1  Started

You can inspect running services with:

$ docker compose ps
NAME                IMAGE                                                   COMMAND                  SERVICE             CREATED             STATUS              PORTS
es                  docker.elastic.co/elasticsearch/elasticsearch:7.17.18   "/bin/tini -- /usr/l…"   es                  2 minutes ago       Up 2 minutes        0.0.0.0:9200->9200/tcp
foodtrucks-web-1    prakhar1989/foodtrucks-web                              "python3 app.py"         web                 2 minutes ago       Up 2 minutes        0.0.0.0:5000->5000/tcp

To stop and remove all containers, networks, and volumes created by Compose:

$ docker compose down -v
[+] Running 3/3
 ✔ Container foodtrucks-web-1  Removed
 ✔ Container es                Removed
 ✔ Network foodtrucks_default  Removed
 ✔ Volume foodtrucks_esdata1   Removed

Congratulations! You have successfully configured and managed a multi-container environment using Docker Compose.