Kubernetes Patterns

Chapter 4. Health Probe

The Health Probe pattern is about how an application can communicate its health state to Kubernetes. To be fully automatable, a cloud-native application must be highly observable by allowing its state to be inferred so that Kubernetes can detect whether the application is up and whether it is ready to serve requests. These observations influence the lifecycle management of Pods and the way traffic is routed to the application.

Problem

Kubernetes regularly checks the container process status and restarts it if issues are detected. However, from practice, we know that checking the process status is not sufficient to decide about the health of an application. In many cases, an application hangs, but its process is still up and running. For example, a Java application may throw an OutOfMemoryError and still have the JVM process running. Alternatively, an application may freeze because it runs into an infinite loop, deadlock, or some thrashing (cache, heap, process). To detect these kinds of situations, Kubernetes needs a reliable way to check the health of applications. That is, not to understand how an application works internally, but a check that indicates whether the application is functioning as expected and capable of serving consumers.

Solution

The software industry has accepted the fact that it is not possible to write bug-free code. Moreover, the chances for failure increase even more when working with distributed applications. As a result, the ...