Demo Service in Swarm Basic Operations

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.

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

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

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

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

4. View Service Logs

Stream logs to troubleshoot or verify startup:

docker service logs first-service

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
   

6. Remove the Service

Clean up by removing the service and all its tasks:

docker service rm first-service
docker service ls

7. Scale Services

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

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

b. Scale Up to Five Replicas

docker service update --replicas 5 second-service

c. Scale Down to Three Replicas

docker service update --replicas 3 second-service

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
   

9. Rollback

If an update misbehaves, revert immediately:

docker service update --rollback second-service
docker service inspect second-service --pretty | grep -i Image

10. Quick Command Reference

Links and References

• Docker Swarm Overview
• Service Commands
• Rolling Updates