Understanding Kubernetes Readiness and Liveness Probes

Distributed systems are hard to manage because they depend on many components, and any failure must be detected, isolated, and repaired automatically. Health checks provide a simple way to verify whether an application instance is functioning correctly, allowing traffic to be routed only to healthy pods.

Kubernetes starts sending traffic to a pod as soon as it starts, but custom health checks (Readiness and Liveness probes) let you fine‑tune this behavior. This article details how to choose and configure these probes.

Health Check Types

Kubernetes offers two main health‑check mechanisms: Readiness and Liveness probes.

Readiness

A Readiness probe tells Kubernetes when an application is ready to accept traffic. If the probe fails, Kubernetes stops sending requests to the pod until it succeeds.

Liveness

A Liveness probe indicates whether an application is still alive. If it fails, Kubernetes kills the pod and creates a new one.

Why Use Probes

Readiness is useful when an app needs time to warm up; Kubernetes will wait before routing traffic. Liveness helps recover from deadlocks or crashes by restarting unhealthy pods.

Probe Types

Kubernetes supports three implementation methods for probes: HTTP, Command, and TCP.

HTTP

HTTP probes send a request to a specified path; a 2xx or 3xx response marks the pod as healthy.

Command

Command probes run a command inside the container; a zero exit code indicates health.

TCP

TCP probes attempt to open a TCP connection to a port; success means the pod is healthy, useful for services like gRPC or FTP.

Configuring Probe Delays

Probes can be tuned with parameters such as initialDelaySeconds, periodSeconds, successThreshold, and failureThreshold. For Liveness probes, setting an appropriate initialDelaySeconds (e.g., using the p99 startup latency) prevents premature restarts.

Summary

Health checks are essential for distributed systems, and Kubernetes provides flexible Readiness and Liveness probes that improve stability, reliability, and uptime of cloud‑native applications.