Linux Foundation Exam CKAD Topic 10 Question 3 Discussion

Actual exam question for Linux Foundation's Certified Kubernetes Application Developer exam

Question #: 3
Topic #: 10

[All Certified Kubernetes Application Developer Questions]

Exhibit:

Context

A pod is running on the cluster but it is not responding.

Task

The desired behavior is to have Kubemetes restart the pod when an endpoint returns an HTTP 500 on the /healthz endpoint. The service, probe-pod, should never send traffic to the pod while it is failing. Please complete the following:

* The application has an endpoint, /started, that will indicate if it can accept traffic by returning an HTTP 200. If the endpoint returns an HTTP 500, the application has not yet finished initialization.

* The application has another endpoint /healthz that will indicate if the application is still working as expected by returning an HTTP 200. If the endpoint returns an HTTP 500 the application is no longer responsive.

* Configure the probe-pod pod provided to use these endpoints

* The probes should use port 8080

ASolution:

In the configuration file, you can see that the Pod has a singleContainer. TheperiodSecondsfield specifies that the kubelet should perform a liveness probe every 5 seconds. TheinitialDelaySecondsfield tells the kubelet that it should wait 5 seconds before performing the first probe. To perform a probe, the kubelet executes the commandcat /tmp/healthyin the target container. If the command succeeds, it returns 0, and the kubelet considers the container to be alive and healthy. If the command returns a non-zero value, the kubelet kills the container and restarts it.
When the container starts, it executes this command:
/bin/sh -c 'touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600'
For the first 30 seconds of the container's life, there is a/tmp/healthyfile. So during the first 30 seconds, the commandcat /tmp/healthyreturns a success code. After 30 seconds,cat /tmp/healthyreturns a failure code.
Create the Pod:
kubectl apply -f https://k8s.io/examples/pods/probe/exec-liveness.yaml
Within 30 seconds, view the Pod events:
kubectl describe pod liveness-exec
The output indicates that no liveness probes have failed yet:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
24s 24s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Pulling pulling image 'k8s.gcr.io/busybox'
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Pulled Successfully pulled image 'k8s.gcr.io/busybox'
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Created Created container with docker id 86849c15382e; Security:[seccomp=unconfined]
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Started Started container with docker id 86849c15382e
After 35 seconds, view the Pod events again:
kubectl describe pod liveness-exec
At the bottom of the output, there are messages indicating that the liveness probes have failed, and the containers have been killed and recreated.
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
37s 37s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Pulling pulling image 'k8s.gcr.io/busybox'
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Pulled Successfully
2s 2s 1 {kubelet worker0} spec.containers{liveness} Warning Unhealthy Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory
Wait another 30 seconds, and verify that the container has been restarted:
kubectl get pod liveness-exec
The output shows thatRESTARTShas been incremented:
NAME READY STATUS RESTARTS AGE
liveness-exec 1/1 Running 1 1m

BSolution:

In the configuration file, you can see that the Pod has a singleContainer. TheperiodSecondsfield specifies that the kubelet should perform a liveness probe every 5 seconds. TheinitialDelaySecondsfield tells the kubelet that it should wait 5 seconds before performing the first probe. To perform a probe, the kubelet executes the commandcat /tmp/healthyin the target container. If the command succeeds, it returns 0, and the kubelet considers the container to be alive and healthy. If the command returns a non-zero value, the kubelet kills the container and restarts it.
When the container starts, it executes this command:
/bin/sh -c 'touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600'
For the first 30 seconds of the container's life, there is a/tmp/healthyfile. So during the first 30 seconds, the commandcat /tmp/healthyreturns a success code. After 30 seconds,cat /tmp/healthyreturns a failure code.
Create the Pod:
kubectl apply -f https://k8s.io/examples/pods/probe/exec-liveness.yaml
Within 30 seconds, view the Pod events:
kubectl describe pod liveness-exec
The output indicates that no liveness probes have failed yet:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
24s 24s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Pulling pulling image 'k8s.gcr.io/busybox'
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Pulled Successfully pulled image 'k8s.gcr.io/busybox'
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Created Created container with docker id 86849c15382e; Security:[seccomp=unconfined]
23s 23s 1 {kubelet worker0} spec.containers{liveness} Normal Started Started container with docker id 86849c15382e
After 35 seconds, view the Pod events again:
kubectl describe pod liveness-exec
At the bottom of the output, there are messages indicating that the liveness probes have failed, and the containers have been killed and recreated.
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
37s 37s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Pulling pulling image 'k8s.gcr.io/busybox'
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Pulled Successfully pulled image 'k8s.gcr.io/busybox'
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Created Created container with docker id 86849c15382e; Security:[seccomp=unconfined]
36s 36s 1 {kubelet worker0} spec.containers{liveness} Normal Started Started container with docker id 86849c15382e
2s 2s 1 {kubelet worker0} spec.containers{liveness} Warning Unhealthy Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory
Wait another 30 seconds, and verify that the container has been restarted:
kubectl get pod liveness-exec
The output shows thatRESTARTShas been incremented:
NAME READY STATUS RESTARTS AGE
liveness-exec 1/1 Running 1 1m

Show Suggested Answer

Suggested Answer: B

by Rasheeda at May 09, 2022, 02:44 PM

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