Cluster Networking

Kubernetes approaches networking somewhat differently than Docker does by default. There are 4 distinct networking problems to solve:

1. Highly-coupled container-to-container communications: this is solved by pods and localhost communications.
2. Pod-to-Pod communications: this is the primary focus of this document.
3. Pod-to-Service communications: this is covered by services.
4. External-to-Service communications: this is covered by services.

Summary

Kubernetes assumes that pods can communicate with other pods, regardless of which host they land on. Every pod gets its own IP address so you do not need to explicitly create links between pods and you almost never need to deal with mapping container ports to host ports. This creates a clean, backwards-compatible model where pods can be treated much like VMs or physical hosts from the perspectives of port allocation, naming, service discovery, load balancing, application configuration, and migration.

There are requirements imposed on how you set up your cluster networking to achieve this.