[atombender]

That is indeed the use case being solved here.

Kubernetes enforces a specific rule: Each pod (a group of containers) must be allocated its own cluster-routable IP address. This vastly simplifies Docker setups: In a way, it containerizes the network, just like Docker containerizes processes. It's the only sane way to manage containers, in my opinion.

This system requires something that can hand out IPs and ensure that they're routable on every machine. That something can be done in different ways, range from extremely simple to rather complex. For example, you could have something that acts like a bridge and coordinates with other nodes to find available IPs, and simply maintains the routing table on the nodes themselves in sync with this shared database (Flannel can run in this mode). Or you could use an SDN-defined overlay network (e.g. Weave).