Swarm Operations

In this lesson, you’ll learn how to:

• Promote and demote Swarm nodes
• Drain nodes for maintenance
• Remove nodes from your cluster

These operations help maintain high availability and streamline cluster management.

Promote and Demote Nodes

Only Swarm manager nodes can orchestrate the cluster. You can elevate a worker node to manager or revert a manager back to a worker. Run these commands on any current manager.

Promote a Worker to Manager

docker node promote worker1

Verify the updated node list:

Demote a Manager to Worker

docker node demote worker1

Confirm the demotion:

Drain a Node for Maintenance

Before patching or upgrading, remove workloads from a node to avoid downtime. The following diagram shows a Swarm cluster with one manager and two workers running a “Web” service.

Drain worker1 to migrate its tasks:

docker node update --availability drain worker1

Check the drain status:

After maintenance, reactivate scheduling:

docker node update --availability active worker1

Now worker1 will accept new tasks:

Remove a Node from the Swarm

To permanently remove a worker node:

1. Drain the node:

   docker node update --availability drain worker2
   

2. Log in to worker2 and leave the swarm:

   docker swarm leave
   

Example confirmation:

Node left the swarm.

At this point, worker2 is safely removed, and your cluster continues with the remaining nodes.

References

• Docker Swarm Overview
• Docker Node Management
• Docker Maintenance Best Practices