The liveness probe in Kubernetes is designed to detect whether a container is still running correctly or has entered a failed or unresponsive state. Its primary purpose is to determine whether a container should be restarted. When a liveness probe fails repeatedly, Kubernetes assumes the container is unhealthy and automatically restarts it to restore normal operation.

Option D correctly describes this behavior. Liveness probes are used to identify situations where an application is running but no longer functioning as expected—for example, a deadlock, infinite loop, or hung process that cannot recover on its own. In such cases, restarting the container is often the most effective remediation, and Kubernetes handles this automatically through the liveness probe mechanism.

Option A is incorrect because readiness probes—not liveness probes—determine whether a container is ready to receive traffic. A container can be alive but not ready, such as during startup or temporary maintenance. Option B is incorrect because startup success is handled by startup probes, which are specifically designed to manage slow-starting applications and delay liveness and readiness checks until initialization is complete. Option C is incorrect because exceeding resource limits is managed by the container runtime and kubelet (for example, OOMKills), not by probes.

Liveness probes can be implemented using HTTP requests, TCP socket checks, or command execution inside the container. If the probe fails beyond a configured threshold, Kubernetes restarts the container according to the Pod’s restart policy. This self-healing behavior is a core feature of Kubernetes and contributes significantly to application reliability.

Kubernetes documentation emphasizes using liveness probes carefully, as misconfiguration can cause unnecessary restarts. However, when used correctly, they provide a powerful way to automatically recover from application-level failures that Kubernetes cannot otherwise detect.

In summary, the liveness probe’s role is to detect when a container is unresponsive and needs to be restarted, making option D the correct and fully verified answer.