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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.

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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.

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Promote a Worker to Manager

Promoting a node requires you to be connected to an active manager. Check your current context with docker info.
Verify the updated node list:

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Demote a Manager to Worker

Confirm the demotion:

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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.
The image illustrates a Docker Swarm setup with three nodes: one manager node and two worker nodes, each labeled with an IP address and a "Web" service.
Drain worker1 to migrate its tasks:
Draining a node stops new tasks from being scheduled and reschedules existing ones on other workers. Ensure your cluster has enough capacity before draining.
Check the drain status: After maintenance, reactivate scheduling:
Now worker1 will accept new tasks:

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Remove a Node from the Swarm

To permanently remove a worker node:
  1. Drain the node:
  2. Log in to worker2 and leave the swarm:
Example confirmation:
At this point, worker2 is safely removed, and your cluster continues with the remaining nodes.

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References

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