How Docker swarm mode does load balancing?

Question

In docker swarm mode (docker engine 1.12+), for the service, what is the load balancing algorithm?

Is it pluginable?

Assuming it is round-robin, is it still needed for a high level load balancer? Since whatever routing algorithm the high level load balancer is using, the load will go to each node evenly.

Answer 1

The algorithm is currently round-robin and I've seen no indication that it's pluginable yet. A higher level load balancer would allow swarm nodes to be taken down for maintenance, but any sticky sessions or other routing features will be undone by the round-robin algorithm in swarm mode.