What is Docker Swarm and why You Need to Start using it

It’s a cluster comprised of a group of physical and virtual machines running the Docker Engine, these are called nodes.

One of the nodes is elected to be the Leader by using the Raft consensus algorithm. He make all the orchestration decisions for the swarm. In case of failure, a new leader it’s automatically elected.

Manager nodes assign tasks to Worker nodes. They can do some other managerial tasks. You want to have an odd number of managers, for reliability purposes. Having to many managers can degrade performance, it’s recommended to have at most 7.