Docker Compose

Docker Compose lets you define and run multi‐container applications from a single YAML file. Instead of managing each docker run command manually, you declare services, networks, and volumes in docker-compose.yaml and launch the entire stack with one command:

docker-compose up

1. Recap: Running Multiple Containers with `docker run`

To illustrate the complexity of manual container orchestration, imagine starting four services individually:

docker run -d --name web mmumshad/simple-webapp
docker run -d --name database mongo
docker run -d --name messaging redis:alpine
docker run -d --name orchestration ansible

Each container runs, but wiring them together (networking, links, ports) quickly becomes tedious.

2. Defining Services in Compose

In docker-compose.yaml, all services and their options live under the services: key:

version: '3'
services:
  web:
    image: mmumshad/simple-webapp

  database:
    image: mongo

  messaging:
    image: redis:alpine

  orchestration:
    image: ansible

Then bring the entire stack up:

docker-compose up

Every configuration change is version‐controlled in your Compose file—no more hunting down individual CLI commands.

3. Sample Voting Application Architecture

We’ll demonstrate Compose using Docker’s sample voting app, composed of:

Voting app (Python web UI): records “cats” or “dogs” votes in Redis.
Worker (.NET): reads votes from Redis and updates PostgreSQL.
PostgreSQL: stores persistent vote counts.
Result app (Node.js web UI): displays tallied results from PostgreSQL.

The image is a diagram of a sample voting application architecture, showing components like a voting app in Python, an in-memory database using Redis, a worker in .NET, and a result app connected to a PostgreSQL database. It also includes a simple voting result table for cats and dogs.

4. Manual Stack Deployment with `docker run`

If images already exist on Docker Hub, you might start containers like this:

# Data layer
docker run -d --name redis redis
docker run -d --name db postgres

# Services
docker run -d --name vote   -p 5000:80 voting-app
docker run -d --name result -p 5001:80 result-app
docker run -d --name worker worker

However, without networking configuration, containers cannot communicate.

4.1 Linking Containers (Deprecated)

The --link flag creates /etc/hosts entries for cross-container DNS:

docker run -d --name redis redis
docker run -d --name db postgres

docker run -d --name vote -p 5000:80 --link redis:redis voting-app
docker run -d --name result -p 5001:80 --link db:db result-app
docker run -d --name worker --link redis:redis --link db:db worker

In your Node.js code, you’d connect via the hostname db:

pg.connect('postgres://postgres@db/postgres', (err, client, done) => {
  if (err) console.error("Waiting for db");
  callback(err, client);
});

Container links are deprecated. Instead, use user‐defined networks as shown in the next sections.

5. From `docker run` to `docker-compose.yaml`

Convert your verified docker run commands into a Compose file:

# Working commands for reference
docker run -d --name redis redis
docker run -d --name db postgres:9.4
docker run -d --name vote   -p 5000:80 --link redis:redis voting-app
docker run -d --name result -p 5001:80 --link db:db result-app
docker run -d --name worker --link db:db --link redis:redis worker

Compose definition:

version: '2'
services:
  redis:
    image: redis

  db:
    image: postgres:9.4

  vote:
    image: voting-app
    ports:
      - "5000:80"
    links:
      - redis

  result:
    image: result-app
    ports:
      - "5001:80"
    links:
      - db

  worker:
    image: worker
    links:
      - redis
      - db

Launch with:

docker-compose up

6. Building Local Images in Compose

If your service images are built locally, specify a build: context instead of image::

version: '2'
services:
  vote:
    build: ./vote
    ports:
      - "5000:80"
    links:
      - redis

  result:
    build: ./result
    ports:
      - "5001:80"
    links:
      - db

  worker:
    build: ./worker
    links:
      - redis
      - db

  redis:
    image: redis

  db:
    image: postgres:9.4

Compose will build these images from each directory’s Dockerfile before starting the containers.

7. Compose File Versions Compared

Different Compose versions introduce new features and schemas. Refer to this summary:

Version	Structure	Highlights
v1	No `services:`	Legacy; no networks or `depends_on`
v2	`services:`	Built‐in network, `depends_on` support
v3	Same as v2	Adds Swarm deployment settings

Examples

Version 1

version: '1'
redis:
  image: redis
db:
  image: postgres:9.4
vote:
  image: voting-app
  ports:
    - "5000:80"
  links:
    - redis

Version 2

version: '2'
services:
  redis:
    image: redis

  db:
    image: postgres:9.4

  vote:
    image: voting-app
    ports:
      - "5000:80"
    depends_on:
      - redis

Version 3

version: '3'
services:
  redis:
    image: redis

  db:
    image: postgres:9.4

  vote:
    image: voting-app
    ports:
      - "5000:80"

For full details, see the Docker Compose file reference.

8. Defining Custom Networks

By default, Compose creates a single bridge network. You can isolate traffic with multiple networks:

The image is a diagram illustrating a Docker Compose setup with components like a voting app, result app, Redis, database, and worker, connected to represent a system architecture.

version: '2'
services:
  redis:
    image: redis
    networks:
      - back-end

  db:
    image: postgres:9.4
    networks:
      - back-end

  vote:
    image: voting-app
    networks:
      - front-end
      - back-end

  result:
    image: result-app
    networks:
      - front-end
      - back-end

  worker:
    image: worker
    networks:
      - back-end

networks:
  front-end: {}
  back-end: {}

Containers on front-end can only communicate with those also on back-end.

Next Steps

Now that you’ve mastered service definitions, version schemas, and custom networks, try creating and running your own docker-compose.yaml configurations in the exercises below.

Introduction

Docker Engine

Docker Image Management

Docker Engine - Security

Docker Engine - Networking

Docker Engine - Storage

Docker Swarm

Kubernetes

Docker Engine Enterprise

Docker Trusted Registry

Disaster Recovery

Docker Compose

1. Recap: Running Multiple Containers with `docker run`

2. Defining Services in Compose

3. Sample Voting Application Architecture

4. Manual Stack Deployment with `docker run`

4.1 Linking Containers (Deprecated)

5. From `docker run` to `docker-compose.yaml`

6. Building Local Images in Compose

7. Compose File Versions Compared

Examples

Version 1

Version 2

Version 3

8. Defining Custom Networks

Next Steps

Links and References

Watch Video

​1. Recap: Running Multiple Containers with docker run

​2. Defining Services in Compose

​3. Sample Voting Application Architecture

​4. Manual Stack Deployment with docker run

​4.1 Linking Containers (Deprecated)

​5. From docker run to docker-compose.yaml

​6. Building Local Images in Compose

​7. Compose File Versions Compared

​Examples

​Version 1

​Version 2

​Version 3

​8. Defining Custom Networks

​Next Steps

​Links and References

Watch Video

1. Recap: Running Multiple Containers with `docker run`

2. Defining Services in Compose

3. Sample Voting Application Architecture

4. Manual Stack Deployment with `docker run`

4.1 Linking Containers (Deprecated)

5. From `docker run` to `docker-compose.yaml`

6. Building Local Images in Compose

7. Compose File Versions Compared

Examples

Version 1

Version 2

Version 3

8. Defining Custom Networks

Next Steps

Links and References