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Module 16 Exercises — Docker Swarm

Exercise 1: Init swarm and create a service

Goal: You form a one-node swarm and run a replicated service. Time estimate: 20 minutes Instructions:

  1. Initialize Swarm (if not already active). 
    docker swarm init
    Swarm initialized: current node (...) is now a manager
  2. Create a service with three replicas. 
    docker service create --name swarm-nginx --publish 8088:80 --replicas 3 nginx:1.27-alpine
    overall progress: 3 out of 3 tasks
  3. List services and tasks. 
    docker service ls
docker service ps swarm-nginx
    REPLICAS   3/3

Expected output: docker service ls shows 3/3 replicas; curl http://localhost:8088 returns nginx HTML (status 200). Hint: If port 8088 is busy, pick another host port and adjust --publish.

Exercise 2: Scale and update

Goal: You scale a service and perform a rolling image update. Time estimate: 25 minutes Instructions:

  1. Scale the service from Exercise 1 to 5 replicas. 
    docker service scale swarm-nginx=5
    overall progress: 5 out of 5 tasks
  2. Update the image tag. 
    docker service update --image nginx:1.28-alpine swarm-nginx
    overall progress: 5 out of 5 tasks
  3. Confirm tasks use the new image. 
    docker service ps swarm-nginx --no-trunc | head -n 6

Expected output: Five running tasks; image column shows nginx:1.28-alpine after update completes. Hint: Watch progress with docker service ps swarm-nginx until all tasks are Running.

Exercise 3: Deploy and remove a stack

Goal: You deploy the module stack file and tear it down cleanly. Time estimate: 25 minutes Instructions:

  1. From modules/16-docker-swarm/examples, deploy the stack. 
    docker stack deploy -c swarm-stack.yaml webstack
    Creating service webstack_web
  2. Verify three replicas and HTTP response. 
    docker stack services webstack
curl -s -o /dev/null -w "%{http_code}\n" http://localhost:8080
    3/3
200
  3. Remove the stack. 
    docker stack rm webstack
    Removing service webstack_web
  4. Remove the Exercise 1 service if you no longer need it. 
    docker service rm swarm-nginx

Expected output: Stack services show 0/0 or disappear after stack rm; port 8080 is free. Hint: You cannot deploy two stacks that publish the same host port—remove Exercise 1 service or change ports in the YAML.