Exec probe configuration in Kubernetes - Step-by-Step Execution

Process Flow - Exec probe configuration

Pod starts

↓

Kubelet runs exec probe

↓

Exec command runs inside container

↓

Command exits with code

↓

Exit code 0?

Yes→Probe success

↓

Exit code != 0?

Yes→Probe failure

↓

Kubelet acts on probe result

The kubelet runs a command inside the container. If the command exits with 0, the probe is successful; otherwise, it fails.

Execution Sample

Kubernetes

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

This probe runs 'cat /tmp/healthy' inside the container every 5 seconds after an initial delay of 5 seconds to check if the container is healthy.

Process Table

Step	Action	Command Run	Exit Code	Probe Result	Kubelet Response
1	Pod starts				Pod running, probe scheduled
2	Wait initialDelaySeconds				Waiting 5 seconds before first probe
3	Run exec probe	cat /tmp/healthy	0	Success	No action needed
4	Wait periodSeconds				Wait 5 seconds before next probe
5	Run exec probe	cat /tmp/healthy	1	Failure	Restart container
6	Container restarts				Pod restarting container
7	Run exec probe	cat /tmp/healthy	0	Success	No action needed

💡 Probe runs repeatedly every periodSeconds; failure triggers container restart.

Status Tracker

Variable	Start	After Step 3	After Step 5	After Step 7
Exit Code	N/A	0	1	0
Probe Result	N/A	Success	Failure	Success
Container State	Starting	Running	Restarting	Running

Key Moments - 3 Insights

Why does the probe fail when the command exits with code 1?

Because in the execution_table at Step 5, the exit code is 1, which means the command did not succeed, so the probe result is Failure, triggering a container restart.

What happens during initialDelaySeconds before the first probe?

As shown in Step 2, the kubelet waits the initialDelaySeconds (5 seconds) before running the first exec probe to give the container time to start.

Does the exec probe run only once?

No, as seen in Steps 3, 5, and 7, the exec probe runs repeatedly every periodSeconds (5 seconds) to continuously check container health.

Visual Quiz - 3 Questions

Look at the execution_table at Step 3. What is the exit code of the exec command?

A 0

B 1

C Success

D Failure

💡 Hint

Check the 'Exit Code' column at Step 3 in the execution_table.

At which step does the kubelet decide to restart the container?

A Step 3

B Step 5

C Step 7

D Step 2

💡 Hint

Look at the 'Kubelet Response' column to find when the container restarts.

If the exec command always exits with 0, how would the container state change over time?

A Container keeps restarting

B Container stays running without restarts

C Container stops after first probe

D Container never starts

💡 Hint

Refer to the 'Container State' in variable_tracker when Exit Code is 0.

Concept Snapshot

Exec probe runs a command inside the container.
If command exits 0, probe succeeds; else fails.
Configured under livenessProbe or readinessProbe.
initialDelaySeconds waits before first run.
periodSeconds sets how often to run.
Failure can restart container.

Full Transcript

Exec probe configuration in Kubernetes means the kubelet runs a command inside the container to check health. The command's exit code determines success (0) or failure (non-zero). The probe runs after an initial delay and repeats periodically. If the probe fails, kubelet can restart the container. This visual trace shows the pod starting, waiting initialDelaySeconds, running the exec command, and reacting based on the exit code. Variables like exit code, probe result, and container state change step by step. Key moments clarify why exit code matters, the role of initial delay, and repeated probe runs. Quiz questions test understanding of exit codes, restart timing, and container state behavior.