K8S Liveness Probe HTTP Request

Liveness Probe HTTPRequest is an element in Kubernetes that allows you to control the liveness of a counter in pods using HTTP. The component allows to query a specific endpoint in the container and infer whether the application is working correctly.

In this article, I will list some common Kubernetes Liveness Probe and httpGet settings. Then I’ll show you a working example of how to properly configure Liveness Probe in your code.

Liveness Probe Settings

Liveness Probe restarts the container when a 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 – Endpoint polling frequency
3. timeoutSeconds – time after which the timeout will expire.
4. successThreshold – the minimum number of successful attempts after which the liveness probe will confirm that the container is operating correctly
5. failThreshold – the number of failed attempts after which the container will be restarted

httpGet options:

1. host – name of the host to connect to
2. scheme – HTTP or HTTPS protocol type
3. path – access path on the HTTP/HTTPS server
4. httpHeaders – Custom headers to set in the request
5. port – The port number that can be accessed in 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 HTTP Request – przykłady

Utwórz pod:

kubectl create -f liveness-pod-example.yaml

Opisz 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 działa.

Żeby sprawdzić, czy działa liveness probe, usuń plik index.html z poda “liveness-request” poniższą komendą.

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

Plik index.html został usunięty, a liveness probe próbował wysłać request do portu 80, ponieważ status odpowiedzi nie znajdował się w zakresie między 200 a 399. Kontener zostanie uruchomiony ponownie. Rezultat zobaczysz poniżej:

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