Among other resources, Docker For AWS template created two auto-scaling groups. One is used for masters and the other for workers. Those security groups have multiple purposes.
If we choose to update the stack to, for example, change the size of the nodes or upgrade Docker server to a newer version, the template will temporarily increase the number of nodes by one and shut down one of the old ones. The replicas that were running on the old server will be moved to the new one. Once the new server is created, it will move to the next, and the next after that, all the way until all the nodes are replaced. The process is very similar to rolling updates we performed by Swarm when updating services. The same process is done whenever we decide to update any aspect of the Docker For AWS stack.
Similarly, if one of the nodes fail health checks, the...