Multi-host networking

In Chapter 10, Single-Host Networking, we discussed how containers communicate on a single Docker host. Now, we have a Swarm that consists of a cluster of nodes or Docker hosts. Containers that are located on different nodes need to be able to communicate with each other. Many techniques can help us to achieve this goal. Docker has chosen to implement an overlay network driver for Docker Swarm. This overlay network allows containers attached to the same overlay network to discover each other and freely communicate with each other. The following is a schema for how an overlay network works:

Overlay network

We have two nodes or Docker hosts with the IP addresses 172.10.0.15 and 172.10.0.16. The values we have chosen for the IP addresses are not important; what is important is that both hosts have a distinct...