How to Use Exec Probe in Kubernetes for Container Health Checks

In Kubernetes, use the exec probe to run a command inside a container to check its health. Define the exec probe in the pod's livenessProbe or readinessProbe section with the command to execute. Kubernetes runs this command periodically and uses its success or failure to manage container lifecycle.

Syntax

The exec probe runs a command inside the container to check its health. It is defined under livenessProbe or readinessProbe in the pod spec.

Key parts:

• exec: The command to run as an array of strings.
• initialDelaySeconds: Time to wait before starting probes.
• periodSeconds: How often to run the probe.
• timeoutSeconds: Time to wait for the command to finish.

yaml

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 5
  periodSeconds: 5
  timeoutSeconds: 1

Example

This example shows a pod with an exec liveness probe that checks if the file /tmp/healthy exists inside the container. If the file is missing, Kubernetes restarts the container.

yaml

apiVersion: v1
kind: Pod
metadata:
  name: exec-probe-example
spec:
  containers:
  - name: busybox
    image: busybox
    command: ["sh", "-c", "touch /tmp/healthy && sleep 3600"]
    livenessProbe:
      exec:
        command:
        - cat
        - /tmp/healthy
      initialDelaySeconds: 5
      periodSeconds: 5
      timeoutSeconds: 1

Output

kubectl get pod exec-probe-example
NAME                 READY   STATUS    RESTARTS   AGE
exec-probe-example   1/1     Running   0          10s

Common Pitfalls

Common mistakes when using exec probes include:

• Using commands that never exit or take too long, causing probe timeouts.
• Not setting initialDelaySeconds, so probes start before the container is ready.
• Using commands that require environment setup not present in the container.
• Confusing exec probe with HTTP or TCP probes.

Always test your command inside the container manually before using it in a probe.

yaml

Wrong:
livenessProbe:
  exec:
    command:
    - tail
    - -f
    - /dev/null
  initialDelaySeconds: 5
  periodSeconds: 5

Right:
livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 5
  periodSeconds: 5

Quick Reference

Field	Description	Example
exec.command	Command array to run inside container	["cat", "/tmp/healthy"]
initialDelaySeconds	Wait time before first probe	5
periodSeconds	Interval between probes	5
timeoutSeconds	Time to wait for command to finish	1
failureThreshold	Failures before marking container unhealthy	3

Key Takeaways

Use the exec probe to run a command inside the container for health checks.

Set initialDelaySeconds to avoid probing before the container is ready.

Ensure the exec command exits quickly and correctly reflects container health.

Test your exec command inside the container before using it in probes.

Exec probes help Kubernetes decide when to restart or stop routing traffic to containers.