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Docker Swarm lets you manage containerized applications as services rather than individual containers. A service in Swarm mode ensures your desired state—replicas, load balancing, rolling updates, and self-healing—are always maintained.

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Table of Contents

  1. Verify Cluster Status
  2. Create Your First Service
  3. Inspect Tasks and Service Details
  4. View Service Logs
  5. Self-Healing Demonstration
  6. Remove the Service
  7. Scale Services
  8. Rolling Updates
  9. Rollback
  10. Quick Command Reference

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1. Verify Cluster Status

Ensure your 6-node Swarm is healthy and managers/workers are all Ready: 
docker node ls
Sample output: 
ID                            HOSTNAME       STATUS  AVAILABILITY  MANAGER STATUS  ENGINE VERSION
kvbhteg486wmj881wp5vkqx53 *  managerone     Ready   Active       Leader          19.03.8
u81imabedhzsu4cawtoz6jh32    managerthree   Ready   Active       Reachable       19.03.8
s2zymqdbtfal66imydx31rlno    managertwo     Ready   Active       Reachable       19.03.8
38oehht7y9bsfs7kcoeji2cvah   workerone      Ready   Active       Active          19.03.8
k4gcc5ooc0mn8xl3f6bm2bp2d    workerthree    Ready   Active       Active          19.03.8
1pqddmhc2f0y79vq9najr841d    workertwo      Ready   Active       Active          19.03.8
Always confirm that at least one manager node is in Leader status before proceeding.

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2. Create Your First Service

Deploy a simple HTTP server using the httpd:alpine image on port 80: 
docker service create \
  --name first-service \
  -p 80:80 \
  httpd:alpine
Verify that the service is up: 
docker service ls
Expected output: 
ID             NAME            MODE         REPLICAS  IMAGE            PORTS
njoes31daltz   first-service   replicated   1/1       httpd:alpine     *:80->80/tcp

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3. Inspect Tasks and Service Details

List the tasks (containers) for first-service: 
docker service ps first-service
For a detailed, human-friendly overview: 
docker service inspect first-service --pretty
Key excerpt: 
Name:           first-service
Service Mode:   Replicated
 Replicas:      1
Image:          httpd:alpine@sha256:...
Ports:
 Published:     80/TCP → 80/TCP

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4. View Service Logs

Stream logs to troubleshoot or verify startup: 
docker service logs first-service

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5. Self-Healing Demonstration

Swarm automatically replaces failed tasks to maintain the desired replica count.
  1. On a worker, find and remove the container: 
    docker container ls
docker rm -f <container_id>
  2. Back on a manager, confirm Swarm recreated it: 
    docker service ps first-service
Swarm will detect that the replica count is below the desired state and launch a new task immediately.

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6. Remove the Service

Clean up by removing the service and all its tasks: 
docker service rm first-service
docker service ls

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7. Scale Services

Run multiple replicas behind Swarm’s built-in load balancer to ensure zero downtime.

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a. Create a Service with Three Replicas

docker service create \
  --name second-service \
  -p 80:80 \
  --replicas 3 \
  httpd:alpine
Verify: 
docker service ls
docker service ps second-service

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b. Scale Up to Five Replicas

docker service update --replicas 5 second-service

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c. Scale Down to Three Replicas

docker service update --replicas 3 second-service

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8. Rolling Updates

Perform seamless image upgrades without stopping traffic.
  1. View current image: 
    docker service inspect second-service --pretty | grep -i Image
  2. Update to a new tag (e.g., httpd:2): 
    docker service update --image httpd:2 second-service
  3. Monitor rollout: 
    docker service ls
docker service ps second-service
During rolling updates, verify your application’s health checks to avoid cascading failures.

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9. Rollback

If an update misbehaves, revert immediately: 
docker service update --rollback second-service
docker service inspect second-service --pretty | grep -i Image

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10. Quick Command Reference

OperationCommand
Verify clusterdocker node ls
Create servicedocker service create --name <svc> -p 80:80 <image>
List servicesdocker service ls
Inspect servicedocker service inspect <svc> --pretty
View service tasksdocker service ps <svc>
Stream logsdocker service logs <svc>
Remove servicedocker service rm <svc>
Scale servicedocker service update --replicas <n> <svc>
Rolling updatedocker service update --image <image:tag> <svc>
Rollbackdocker service update --rollback <svc>

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