Kubernetes Liveness Probe – HTTPRequest

Liveness Probe HTTPRequest is an element in Kubernetes, thanks to which you can control the state of life of a counter in Pods using the HTTP protocol. The component allows you to send queries to a given endpoint in the container and infer whether the application is working correctly.

In this article, I will list some common settings of Kubernetes Liveness Probe and httpGet options. Then, I’ll show you a working example of how you can set up Liveness Probe correctly in your code.

Liveness Probe settings

Liveness Probe restarts the container when the given endpoint returns a status higher than 399. This feature also has some useful settings such as: 

1. initialDelaySeconds – time after which Liveness Probe should start polling the endpoint 
2. periodSeconds – the frequency of polling the endpoint 
3. timeoutSeconds – time after which the timeout will expire. 
4. successThreshold – the minimum number of successful attempts after which the probe will determine the correct operation of the container 
5. failureThreshold – number of failed attempts after which the container will be restarted 

httpGet options: 

1. host – Host name to connect to
2. scheme – Protocol type HTTP or HTTPS
3. path – Path to access on the HTTP/HTTPS server
4. httpHeaders– Custom headers to set in the request 
5. port – Port number to access on the container 

# YAML example
# liveness-pod-example.yaml
#
apiVersion: v1 
kind: Pod 
metadata: 
  name: liveness-request 
spec: 
  containers: 
  - name: liveness 
    image: nginx 
    ports: 
        - containerPort: 80 
    livenessProbe: 
      httpGet: 
        path: / 
        port: 80 
      initialDelaySeconds: 2 #Default 0 
      periodSeconds: 2 #Default 10 
      timeoutSeconds: 1 #Default 1 
      successThreshold: 1 #Default 1 
      failureThreshold: 3 #Default 3 

Liveness Probe – example

Create pod:

kubectl create -f liveness-pod-example.yaml

Describe the pod:

kubectl describe pod liveness-request  

Restart Count:  0
.
.
.
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled <unknown> default-scheduler Successfully assigned example-dc/liveness-request to dcpoz-d-sou-k8swor3
Normal Pulling 4m45s kubelet, dcpoz-d-sou-k8swor3 Pulling image "nginx"
Normal Pulled 4m42s kubelet, dcpoz-d-sou-k8swor3 Successfully pulled image "nginx"
Normal Created 4m42s kubelet, dcpoz-d-sou-k8swor3 Created container liveness
Normal Started 4m42s kubelet, dcpoz-d-sou-k8swor3 Started container liveness

Pod works great, no issue count.

To check if liveness probe works, remove index.html file from “liveness-request” pod.

kubectl exec -it liveness-request -- rm /usr/share/nginx/html/index.html 

kubectl describe pod liveness-request 

Restart Count: 1
.
.
.
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled <unknown> default-scheduler Successfully assigned example-dc/liveness-request to dcpoz-d-sou-k8swor3
Normal Pulling 9s (x2 over 11m) kubelet, dcpoz-d-sou-k8swor3 Pulling image "nginx"
Warning Unhealthy 9s (x3 over 13s) kubelet, dcpoz-d-sou-k8swor3 Liveness probe failed: HTTP probe failed with statuscode: 403
Normal Killing 9s kubelet, dcpoz-d-sou-k8swor3 Container liveness failed liveness probe, will be restarted
Normal Pulled 7s (x2 over 11m) kubelet, dcpoz-d-sou-k8swor3 Successfully pulled image "nginx"
Normal Created 7s (x2 over 11m) kubelet, dcpoz-d-sou-k8swor3 Created container liveness
Normal Started 7s (x2 over 11m) kubelet, dcpoz-d-sou-k8swor3 Started container liveness