Certified Kubernetes Application Developer (CKAD) Study Guide, 2nd Edition

Chapter 14. Container Probes

Applications running in containers do not operate under the premise of “fire and forget.” Once Kubernetes starts the container, you’ll want to know if the application is ready for consumption and is still working as expected in an hour, a week, or a month. A health probe is a periodically running mini-process that asks the application for its status and takes action upon certain conditions.

In this chapter, we’ll discuss container health probes—more specifically, readiness, liveness, and startup probes. You’ll learn about the different health verification methods and how to define them for the proper use cases.

Coverage of Curriculum Objectives

This chapter addresses the following curriculum objective:

• Implement probes and health checks

Working with Probes

Even with the best testing strategy, it’s nearly impossible to find all bugs before deploying software to a production environment. That’s especially true for failure situations that occur only after operating the software for an extended period of time. It’s not uncommon to see memory leaks, deadlocks, infinite loops, and similar conditions crop up once end users put the application under load.

Proper monitoring can help with identifying those issues; however, you still need to act to mitigate the situation. First, you’ll likely want to restart the application to prevent further outages. Second, the development team needs to identify the underlying root cause and fix the application’s code. ...