Deployment using all three Kubernetes probes

Full Example YAML

Here’s a deployment using all three Kubernetes probes:

containers:
  - name: api
    image: my-api:latest

    startupProbe:
      httpGet:
        path: /readyz
        port: 5000
      failureThreshold: 20
      periodSeconds: 15

    readinessProbe:
      httpGet:
        path: /readyz
        port: 5000
      initialDelaySeconds: 5
      periodSeconds: 10
      failureThreshold: 3

    livenessProbe:
      httpGet:
        path: /healthz
        port: 5000
      initialDelaySeconds: 30
      periodSeconds: 20
      failureThreshold: 3

Now let’s break down what Kubernetes is actually doing here.

---

startupProbe

startupProbe:
  httpGet:
    path: /readyz
    port: 5000
  failureThreshold: 20
  periodSeconds: 15

This tells Kubernetes:

Check /readyz every 15 seconds.
Allow 20 failures before killing the container.

Calculation:

15 seconds × 20 failures = 300 seconds

So Kubernetes gives the application:

5 minutes to fully start

before deciding:

“The application failed to start.”

Default Values

If not specified, Kubernetes uses:

periodSeconds: 10
timeoutSeconds: 1
failureThreshold: 3
successThreshold: 1

Which means by default:

10 seconds × 3 failures = 30 seconds

Your application may only get:

~30 seconds

before Kubernetes decides startup failed.

This is why slow-starting applications often need a custom startupProbe.

Common Real-World Use Cases

• Java applications
• ML workloads
• applications loading huge caches
• Python/Gunicorn services
• applications waiting for database migrations

The important part:

A startup probe failure itself is NOT the issue.

The issue happens only when failures continue beyond the threshold.

---

readinessProbe

readinessProbe:
  httpGet:
    path: /readyz
    port: 5000
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

This tells Kubernetes:

Wait 5 seconds after container start.
Then check /readyz every 10 seconds.
If it fails 3 consecutive times:
remove the pod from Service traffic.

Calculation:

10 seconds × 3 failures = 30 seconds

If the application cannot respond successfully for:

30 continuous seconds

the pod becomes:

NotReady

But importantly:

The container is NOT restarted.

Traffic simply stops flowing to it temporarily.

Default Values

If not configured, Kubernetes defaults to:

initialDelaySeconds: 0
periodSeconds: 10
timeoutSeconds: 1
failureThreshold: 3
successThreshold: 1

This means Kubernetes starts checking almost immediately.

That can become dangerous for applications that:

• take time to boot
• warm caches
• establish DB connections
• initialize workers

Important Concept

A readiness failure usually means:

"Do not send traffic right now."

It does NOT mean:

"The application is dead."

This distinction is extremely important in production.

---

livenessProbe

livenessProbe:
  httpGet:
    path: /healthz
    port: 5000
  initialDelaySeconds: 30
  periodSeconds: 20
  failureThreshold: 3

This tells Kubernetes:

Wait 30 seconds before starting checks.
Then check /healthz every 20 seconds.
If it fails 3 consecutive times:
restart the container.

Calculation:

20 seconds × 3 failures = 60 seconds

If health checks fail continuously for:

60 seconds

Kubernetes assumes:

“The application is unhealthy or stuck.”

and restarts the container automatically.

Default Values

Kubernetes defaults:

initialDelaySeconds: 0
periodSeconds: 10
timeoutSeconds: 1
failureThreshold: 3
successThreshold: 1

Which effectively means:

10 seconds × 3 failures = 30 seconds

before restart behavior begins.

Common Mistake

Many teams configure aggressive liveness probes like:

timeoutSeconds: 1

During:

• CPU spikes
• GC pauses
• dependency slowness
• temporary latency

the application may briefly respond slowly.

This can accidentally trigger unnecessary restarts.

---

The Most Important Thing to Understand

Many engineers panic immediately when they see:

Readiness probe failed

or:

Liveness probe failed

But probes are designed to fail occasionally.

The real question is:

Did the failures exceed the threshold?

Because Kubernetes only takes action after repeated failures over time.

That’s why these settings matter so much:

failureThreshold
periodSeconds
timeoutSeconds
initialDelaySeconds

Together, they control:

• how patient Kubernetes should be
• when traffic should stop
• when restarts should happen
• how tolerant the system should be during spikes

---

Probe	What Happens on Failure?
startupProbe	Container may be killed if startup takes too long
readinessProbe	Pod stops receiving traffic
livenessProbe	Container gets restarted

---

Kubernetes probes are not meant to punish applications.

They are safety mechanisms.

The goal is to:

• avoid sending traffic to unhealthy pods
• restart stuck applications
• allow slow startups safely

Once you understand probe thresholds, Kubernetes behavior suddenly becomes much easier to debug.