What is the difference between liveness, readiness, and startup probes?
What they are really testing: Whether you understand that each probe has a distinct effect (restart vs remove from traffic vs gate startup) and the damage a misconfigured liveness probe can do.
A real interview question
What is the difference between liveness, readiness, and startup probes?
What most people say
drag me
“They are health checks that tell Kubernetes whether the container is working.”
It lumps all three together. The whole point is that they do different things, restart vs pull from traffic vs gate startup, and conflating them leads to restart loops and dropped traffic.
The follow-ups they ask next
Why should a liveness probe not check a database connection?
If the database blips, every replica fails liveness and gets restarted simultaneously, turning a dependency issue into a self-inflicted outage. Dependency health belongs in readiness (pull from traffic), not liveness (restart).
Your app takes 60s to start and keeps getting killed during boot. What fixes it?
A startup probe (or a longer initialDelay/failureThreshold) that gates liveness/readiness until the app is up, so a slow but normal start is not treated as a failure.
What the interviewer is listening for
- Liveness=restart, readiness=remove from traffic, startup=gate
- Knows readiness does not restart
- Warns about aggressive/dependency-checking liveness
What sinks the answer
- Treats all three as the same
- Puts dependency checks in liveness
- Unaware of startup probes for slow apps
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“Liveness [asks if the container is healthy, fails to a restart]. Readiness [asks if it can serve now, fails by removing it from Service endpoints, no restart]. Startup [gates the other two for slow-starting apps]. The danger: [an aggressive or dependency-checking liveness probe causes restart loops], so [liveness checks the app, dependencies go in readiness].”
Keep going with kubernetes
Foundation
What problem does Kubernetes solve, and what does it actually do for you?
Foundation
What are the main components of a Kubernetes cluster (control plane and nodes)?
Foundation
What is a Pod, and why do you use a Deployment instead of creating Pods directly?
Foundation
What is a Service in Kubernetes, and what are the main types?
Junior
When would you use a Deployment versus a StatefulSet versus a DaemonSet?
Junior
How do you inject configuration and secrets into a pod, and what is the catch with Kubernetes Secrets?
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