Why probes keep applications healthy in Kubernetes - Visual Breakdown

Process Flow - Why probes keep applications healthy

Start Application Pod

↓

Kubelet runs Probes

↓

Perform Liveness Probe

↓

Is Pod Alive?

No→Restart Pod

Yes↓

Perform Readiness Probe

↓

Is Pod Ready?

No→Remove Pod from Service

Yes↓

Pod serves traffic

↓

Repeat Probes Periodically

Kubernetes uses probes to check if an application is alive and ready. If not alive, it restarts the pod. If not ready, it stops sending traffic to it.

Execution Sample

Kubernetes

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10

This liveness probe checks the /healthz endpoint every 10 seconds after waiting 5 seconds initially.

Process Table

Step	Probe Type	Probe Action	Probe Result	Kubelet Action	Pod State
1	Liveness	Check /healthz	Success	No action	Running
2	Readiness	Check /ready	Success	Pod in service	Serving traffic
3	Liveness	Check /healthz	Failure	Restart Pod	Restarting
4	Liveness	Check /healthz	Success	No action	Running
5	Readiness	Check /ready	Failure	Remove from service	Not serving traffic
6	Readiness	Check /ready	Success	Add to service	Serving traffic
7	Liveness	Check /healthz	Success	No action	Running

💡 Probes run continuously to keep pod healthy and traffic routed correctly.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7
Pod State	Starting	Running	Serving traffic	Restarting	Running	Not serving traffic	Serving traffic	Running
Traffic Routing	None	Routed	Routed	None	None	None	Routed	Routed

Key Moments - 3 Insights

Why does the pod restart after a liveness probe failure?

Because the liveness probe failure means the pod is unhealthy and cannot recover, so Kubernetes restarts it to restore health (see execution_table step 3).

Why is traffic removed from the pod after a readiness probe failure?

Readiness probe failure means the pod is not ready to serve requests, so Kubernetes stops sending traffic to avoid errors (see execution_table step 5).

Can a pod be running but not serving traffic?

Yes, if the readiness probe fails but liveness probe passes, the pod runs but is removed from service (see execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution_table, what action does Kubernetes take at step 3 when the liveness probe fails?

A Restart the pod

B Remove pod from service

C Do nothing

D Send traffic to pod

💡 Hint

Check the 'Kubelet Action' column at step 3 in the execution_table.

At which step does the pod stop serving traffic due to readiness probe failure?

A Step 2

B Step 4

C Step 5

D Step 7

💡 Hint

Look at the 'Pod State' and 'Kubelet Action' columns for readiness probe failures.

If the readiness probe always succeeds, how would the traffic routing change in the variable_tracker?

A Traffic would never be routed

B Traffic would always be routed to the pod

C Traffic would be removed intermittently

D Pod would restart frequently

💡 Hint

Check the 'Traffic Routing' row in variable_tracker and relate it to readiness probe results.

Concept Snapshot

Kubernetes probes check pod health:
- Liveness probe: restarts pod if unhealthy
- Readiness probe: controls traffic routing
- Probes run periodically
- Keeps apps healthy and responsive

Full Transcript

Kubernetes uses liveness and readiness probes to keep applications healthy. The liveness probe checks if the pod is alive; if it fails, Kubernetes restarts the pod to fix issues. The readiness probe checks if the pod is ready to serve traffic; if it fails, Kubernetes stops sending traffic to avoid errors. These probes run repeatedly to monitor pod health and traffic routing. This process ensures applications stay healthy and responsive.