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In this step-by-step tutorial, you’ll learn how to orchestrate a multi-service voting application using Docker Compose. By the end, you’ll have a running stack that includes Redis, PostgreSQL, a voting frontend, a worker processor, and a results dashboard.

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Prerequisites

  • Docker Engine installed (version ≥ 19.03)
  • Basic familiarity with docker CLI
  • A terminal/SSH session on Linux, macOS, or Windows WSL

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Step 1: Install Docker Compose

Docker Compose isn’t bundled with Docker Engine by default. Install it on Linux with: 
sudo curl -L "https://github.com/docker/compose/releases/download/1.16.1/docker-compose-$(uname -s)-$(uname -m)" \
  -o /usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose
docker-compose --version
Expected output: 
docker-compose version 1.16.1, build 1719ceb
Replace 1.16.1 with the latest stable release. See the Compose releases on GitHub for details.

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Step 2: Clean Up Existing Containers

Before deploying, stop any previous demo containers: 
# List running containers
docker ps

# Stop containers by ID or prefix
docker stop 69 54 5b 2f 0b

# Verify all relevant containers are stopped
docker ps
Stopping containers will terminate running services. Ensure you don’t have unsaved data in those containers.

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Step 3: Define Services in docker-compose.yml

Create a file named docker-compose.yml with the following content. It leverages Compose file format version 3. 
version: '3'
services:
  redis:
    image: redis

  db:
    image: postgres:9.4

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

  worker:
    image: worker-app
    depends_on:
      - db
      - redis

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

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Service Overview

ServiceImagePortsDescription
redisredis–In-memory queue for incoming votes
dbpostgres:9.4–Persistent storage for vote records
votevoting-app5000→80Frontend where users cast their vote
workerworker-app–Processes queued votes into the PostgreSQL DB
resultresult-app5001→80Displays aggregated vote results
The depends_on key ensures containers start in the correct order, but it doesn’t wait for health checks. Consider adding healthchecks for production workloads.
See the Compose file reference for advanced options.

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Step 4: Deploy the Stack

From the directory containing docker-compose.yml, run: 
docker-compose up -d
This command will pull images, create a default network, and start all five containers. Container names are prefixed by your folder name (e.g., root_redis_1). Verify everything is up: 
docker ps
You should see containers for Redis, PostgreSQL, vote, worker, and result.

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Step 5: Access the Application

Cast a vote on the first page, then switch to the results page to see real-time counts.
The image shows a webpage titled "Cats vs Dogs!" with two buttons labeled "CATS" and "DOGS," where "DOGS" is selected. It also mentions that you can change your vote and displays a container ID at the bottom.

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Clean Up

When you’re done testing, stop and remove all services with: 
docker-compose down
This command stops containers and removes the network. Volumes and images remain unless you add the --volumes or --rmi all flags.

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References and Further Reading

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