Using Docker

Chapter 11. Networking and Service Discovery

The line between service discovery and networking can become surprisingly blurred in a container context. Service discovery is the process of automatically providing clients¹ of a service with connection information (normally IP address and port) for an appropriate² instance of that service. This problem is easy in a static, single-host system where there is exactly one instance of everything, but is much more complicated in a distributed system with multiple instances of services that come and go over time. One way to approach discovery is for the client simply to request the service by name (e.g., db or api), and do some magic on the backend to have this resolve to the appropriate location. This “magic” can take the form of simple ambassador containers, a service discovery solution such as Consul, a networking solution such as Weave (which includes service discovery features), or some combination of the previous.

For our purposes, networking can be regarded as the process of connecting containers together. It does not involve plugging in physical Ethernet cables, although it often involves software equivalents such as veth. Container networking starts from the assumption that there is a route available between hosts, whether that route involves traversing the public Internet or just a fast local switch.

So, service discovery allows clients to discover instances, and networking takes care of putting the connections in place. Networking ...