Observability (18%)

Liveness and readiness probes

kubernetes.io > Documentation > Tasks > Configure Pods and Containers > Configure Liveness and Readiness Probes

Create an nginx pod with a liveness probe that just runs the command ‘ls’. Save its YAML in pod.yaml. Run it, check its probe status, delete it.

kubectl run nginx --image=nginx --restart=Never --dry-run=client -o yaml > pod.yaml
vi pod.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    livenessProbe: # our probe
      exec: # add this line
        command: # command definition
        - ls # ls command
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
kubectl create -f pod.yaml
kubectl describe pod nginx | grep -i liveness # run this to see that liveness probe works
kubectl delete -f pod.yaml

Modify the pod.yaml file so that liveness probe starts kicking in after 5 seconds whereas the interval between probes would be 5 seconds. Run it, check the probe, delete it.

kubectl explain pod.spec.containers.livenessProbe # get the exact names
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    livenessProbe: 
      initialDelaySeconds: 5 # add this line
      periodSeconds: 5 # add this line as well
      exec:
        command:
        - ls
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
kubectl create -f pod.yaml
kubectl describe po nginx | grep -i liveness
kubectl delete -f pod.yaml

Create an nginx pod (that includes port 80) with an HTTP readinessProbe on path ‘/’ on port 80. Again, run it, check the readinessProbe, delete it.

kubectl run nginx --image=nginx --dry-run=client -o yaml --restart=Never --port=80 > pod.yaml
vi pod.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    ports:
      - containerPort: 80 # Note: Readiness probes runs on the container during its whole lifecycle. Since nginx exposes 80, containerPort: 80 is not required for readiness to work.
    readinessProbe: # declare the readiness probe
      httpGet: # add this line
        path: / #
        port: 80 #
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
kubectl create -f pod.yaml
kubectl describe pod nginx | grep -i readiness # to see the pod readiness details
kubectl delete -f pod.yaml

Lots of pods are running in qa,alan,test,production namespaces. All of these pods are configured with liveness probe. Please list all pods whose liveness probe are failed in the format of <namespace>/<pod name> per line.

A typical liveness probe failure event

LAST SEEN   TYPE      REASON      OBJECT              MESSAGE
22m         Warning   Unhealthy   pod/liveness-exec   Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory

collect failed pods namespace by namespace

kubectl get ns # check namespaces
kubectl -n qa get events | grep -i "Liveness probe failed"
kubectl -n alan get events | grep -i "Liveness probe failed"
kubectl -n test get events | grep -i "Liveness probe failed"
kubectl -n production get events | grep -i "Liveness probe failed"

Logging

Create a busybox pod that runs ‘i=0; while true; do echo “$i: $(date)"; i=$((i+1)); sleep 1; done’. Check its logs

kubectl run busybox --image=busybox --restart=Never -- /bin/sh -c 'i=0; while true; do echo "$i: $(date)"; i=$((i+1)); sleep 1; done'
kubectl logs busybox -f # follow the logs

Debugging

Create a busybox pod that runs ‘ls /notexist’. Determine if there’s an error (of course there is), see it. In the end, delete the pod

kubectl run busybox --restart=Never --image=busybox -- /bin/sh -c 'ls /notexist'
# show that there's an error
kubectl logs busybox
kubectl describe po busybox
kubectl delete po busybox

Create a busybox pod that runs ‘notexist’. Determine if there’s an error (of course there is), see it. In the end, delete the pod forcefully with a 0 grace period

kubectl run busybox --restart=Never --image=busybox -- notexist
kubectl logs busybox # will bring nothing! container never started
kubectl describe po busybox # in the events section, you'll see the error
# also...
kubectl get events | grep -i error # you'll see the error here as well
kubectl delete po busybox --force --grace-period=0

Get CPU/memory utilization for nodes (metrics-server must be running)

kubectl top nodes
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