Kubernetes Patterns, 2nd Edition

Chapter 13. Service Discovery

The Service Discovery pattern provides a stable endpoint through which consumers of a service can access the instances providing the service. For this purpose, Kubernetes provides multiple mechanisms, depending on whether the service consumers and producers are located on or off the cluster.

Problem

Applications deployed on Kubernetes rarely exist on their own, and usually they have to interact with other services within the cluster or systems outside the cluster. The interaction can be initiated internally within the service or through external stimulus. Internally initiated interactions are usually performed through a polling consumer: either after startup or later, an application connects to another system and starts sending and receiving data. Typical examples are an application running within a Pod that reaches a file server and starts consuming files, or a message that connects to a message broker and starts receiving or sending messages, or an application that uses a relational database or a key-value store and starts reading or writing data.

The critical distinction here is that the application running within the Pod decides at some point to open an outgoing connection to another Pod or external system and starts exchanging data in either direction. In this scenario, we don’t have an external stimulus for the application, and we don’t need any additional setup in Kubernetes.

To implement the patterns described in Chapter 7, “Batch Job”, or ...