Demo Docker Stack

In this lesson, we'll deploy the Example Voting App using Docker Stacks on a Swarm cluster. We start by upgrading our Compose file to version 3, deploy it as a stack, verify running services, and then scale the voting service.

1. Prepare the Docker Compose File (Version 3)

Below is the upgraded Compose file in version 3 format. Save this as docker-stack.yml on your Swarm manager:

version: '3'
services:
  redis:
    image: redis
  db:
    image: postgres:9.4
  vote:
    image: dockersamples/examplevotingapp_vote
    ports:
      - "5000:80"
  worker:
    image: dockersamples/examplevotingapp_worker
  result:
    image: dockersamples/examplevotingapp_result
    ports:
      - "5001:80"

The dockersamples images are available on Docker Hub.

docker swarm init

2. Deploy the Stack

1. SSH into your Swarm manager and create a project directory:

   mkdir ~/voting-app-stack && cd ~/voting-app-stack
   

2. Place the docker-stack.yml file in this directory.
3. Deploy the stack:

   docker stack deploy voting-app-stack --compose-file docker-stack.yml
   

   You should see output similar to:

   Creating network voting-app-stack_default
   Creating service voting-app-stack_redis
   Creating service voting-app-stack_db
   Creating service voting-app-stack_vote
   Creating service voting-app-stack_worker
   Creating service voting-app-stack_result
   

Verify all services are up:

docker service ls

3. Inspect Running Tasks

On any manager or worker node, list the active containers to ensure tasks are distributed:

docker ps

Example output:

CONTAINER ID  IMAGE                                           NAMES
3940e228ce02  dockersamples/examplevotingapp_result:latest    voting-app-stack_result.1.abcde
9348d1d3d7f5  postgres:9.4                                    voting-app-stack_db.1.fghij

4. Access the Voting Application

Open a browser and navigate to:

• Voting interface: http://<manager-ip>:5000
• Results dashboard: http://<manager-ip>:5001

5. Scale the Voting Service

To handle higher traffic, update docker-stack.yml by adding the deploy.replicas setting under the vote service:

services:
  vote:
    image: dockersamples/examplevotingapp_vote
    ports:
      - "5000:80"
    deploy:
      replicas: 2

Redeploy the updated stack:

docker stack deploy voting-app-stack --compose-file docker-stack.yml

Confirm that the voting service now has two replicas:

docker service ls

Inspect each task:

docker service ps voting-app-stack_vote

Links and References

• Docker Stack Deploy
• Docker Compose File Reference
• Docker Swarm Overview

This demonstrates how to deploy, verify, and scale services using Docker Stacks in a Swarm cluster.