Demo Docker Compose

In this guide, you’ll learn how to migrate a basic Docker Compose setup from version 1 to version 3. We’ll remove deprecated options, configure environment variables for PostgreSQL, and explore build and deployment best practices.

1. Starting with the Basic Compose File (Version 1)

Here’s a simple Compose file in version 1 syntax defining five services:

redis:
  image: redis

db:
  image: postgres:9.4

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

worker:
  image: worker-app
  links:
    - db
    - redis

result:
  image: result-app
  ports:
    - "5011:80"
  links:
    - db

Version 1 is straightforward but lacks support for:

Automatic network creation
Built-in DNS service discovery
Named volumes and advanced deployment options

2. Upgrading to Version 3

Compose version 3 unlocks Docker Swarm compatibility, automatic networking, and enhanced resource definitions. Follow these steps:

Add version: "3" at the top.
Nest all services under the services: key.
Remove links:—service names now resolve via DNS.

version: "3"
services:
  redis:
    image: redis
  db:
    image: postgres:9.4
  vote:
    image: voting-app
    ports:
      - "5000:80"
  worker:
    image: worker-app
  result:
    image: result-app
    ports:
      - "5001:80"

In version 3, Docker Compose automatically creates a default network. Services communicate by name, e.g., redis ↔ db.

The image shows a section of the Docker documentation website, specifically the Compose and Docker compatibility matrix, listing different Compose file versions and their corresponding Docker versions.

3. Specifying Build Options

You can define how images are built directly in your Compose file. Examples from Docker’s docs: Simple build context:

version: "3.9"
services:
  webapp:
    build: ./dir

Custom Dockerfile and build args:

version: "3.9"
services:
  webapp:
    build:
      context: ./dir
      dockerfile: Dockerfile-alternate
      args:
        buildno: 1

Build with image tag:

services:
  webapp:
    build: ./dir
    image: webapp:tag

In Swarm mode, docker stack deploy ignores the build option. You must build images locally with docker build or push them to a registry before deploying.

4. Deploying with Docker Compose

With your version 3 Compose file in place, start all services:

docker-compose up

Sample output:

WARNING: The Docker Engine you're using is running in swarm mode.
Compose does not use swarm mode to deploy services to multiple nodes
in a swarm. All containers will be scheduled on the current node.
To deploy your application across the swarm, use `docker stack deploy`.
Creating network "code_default" with the default driver
Creating code_redis_1    ... done
Creating code_db_1       ... done
Creating code_vote_1     ... done
Creating code_worker_1   ... done
Creating code_result_1   ... done

Here, code_default is the auto-generated network, and all containers are prefixed with the project name (code_).

If you want to run in detached mode, add -d:

docker-compose up -d

5. Handling PostgreSQL Initialization

On first run, PostgreSQL requires a superuser password. Without it, you’ll see:

db_1  | Error: Database is uninitialized and superuser password is not specified.
db_1  | You must specify POSTGRES_PASSWORD for the superuser. Use
db_1  | "-e POSTGRES_PASSWORD=password" to set it in "docker run".

Add environment variables under the db service:

version: "3"
services:
  redis:
    image: redis
  db:
    image: postgres:9.4
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
  vote:
    image: voting-app
    ports:
      - "5000:80"
  worker:
    image: worker-app
  result:
    image: result-app
    ports:
      - "5001:80"

Restart in detached mode:

docker-compose up -d

PostgreSQL Environment Variables

Variable	Description
POSTGRES_USER	Superuser name (default: `postgres`)
POSTGRES_PASSWORD	Superuser password (required on init)

6. Verifying the Setup

Once all containers are running, open your browser and test the apps:

Voting app: http://localhost:5000
Results app: http://localhost:5001

Cast a vote for one option (e.g., cats).
Confirm the result updates correctly.
Vote again (e.g., dogs) and verify real-time results.

Your Docker Compose setup is now:

Version 3 compliant
Automatically networked
Securely initializing PostgreSQL

Resource	Description
Docker Documentation	Official guides and references
Kubernetes Basics	Overview of container orchestration (K8s)
Terraform Registry	Modules for automated infrastructure provisioning

Introduction

Docker Engine

Docker Image Management

Docker Engine - Security

Docker Engine - Networking

Docker Engine - Storage

Docker Compose

Docker Swarm

Kubernetes

Docker Engine Enterprise

Docker Trusted Registry

Disaster Recovery

Demo Docker Compose

1. Starting with the Basic Compose File (Version 1)

2. Upgrading to Version 3

3. Specifying Build Options

4. Deploying with Docker Compose

5. Handling PostgreSQL Initialization

PostgreSQL Environment Variables

6. Verifying the Setup

Links and References

Further Reading

Watch Video

​1. Starting with the Basic Compose File (Version 1)

​2. Upgrading to Version 3

​3. Specifying Build Options

​4. Deploying with Docker Compose

​5. Handling PostgreSQL Initialization

​PostgreSQL Environment Variables

​6. Verifying the Setup

​Links and References

​Further Reading

Watch Video

1. Starting with the Basic Compose File (Version 1)

2. Upgrading to Version 3

3. Specifying Build Options

4. Deploying with Docker Compose

5. Handling PostgreSQL Initialization

PostgreSQL Environment Variables

6. Verifying the Setup

Links and References

Further Reading