Glossary · Monitoring

Readiness Probe

A readiness probe is a check that tells an orchestrator or load balancer whether an instance is ready to receive traffic, without restarting it.

Updated November 4, 2026

A readiness probe is a health check used to decide whether an instance should receive requests right now. If it fails, the instance is removed from the load balancer's pool but is not killed. When it passes again, traffic resumes.

Why it matters

A process can be running yet unable to serve: it may still be loading data, warming caches, waiting for a database, or temporarily overloaded. Sending users to it produces errors. Readiness checks keep traffic away until the instance is genuinely ready, enabling zero-downtime deployments and recovery from brief overload.

Example

In Kubernetes:

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

After three consecutive failures, the pod stops receiving traffic. A good /ready endpoint verifies things the instance needs to answer requests, such as a database connection, but is cheap and does not run heavy queries. Keep it distinct from a liveness probe, which decides whether to restart.

Common mistakes

  • Making readiness depend on every downstream service, so one outage removes all instances and turns a partial failure into a total one.
  • Using the same endpoint and thresholds as liveness.
  • Setting no initial delay for slow-starting applications.
  • Returning 200 from a static page that proves nothing.

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