1장. Understanding networking

The pod network is a flat network space where every pod in the cluster receives its own unique IP address. This network is managed by the Container Network Interface (CNI) plugin. The CNI plugin is responsible for wiring each pod into the cluster network.

This design allows pods to communicate directly with each other using their IP addresses, regardless of which node they are running on. However, these pod IP addresses are ephemeral. This means the IP addresses are destroyed when the pod is destroyed and a new IP address is assigned when a new pod is created. Because of this, you should never rely on pod IP addresses directly for long-lived communication.

A service is a networking object that provides a single, stable virtual IP address, called a ClusterIP, and a DNS name for a logical group of pods.

When a request is sent to a the ClusterIP of the service, OpenShift Container Platform automatically load balances the traffic to one of the healthy pods backing that service. OpenShift Container Platform uses Kubernetes labels and selectors to keep track of which pods belong to which service. This abstraction makes your applications resilient because individual pods can be created or destroyed without affecting the applications trying to reach them.