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Setting up Active and Passive health checks

Learn to setup active and passive health checking using the Kong Ingress Controller. This configuration allows Kong to automatically short-circuit requests to specific Pods that are mis-behaving in your Kubernetes Cluster.

Before you begin ensure that you have Installed Kong Ingress Controller in your Kubernetes cluster and are able to connect to Kong.

Prerequisites

Install Kong

You can install Kong in your Kubernetes cluster using Helm.

Add the Kong Helm charts:

 helm repo add kong https://charts.konghq.com
 helm repo update

Install Kong Ingress Controller and Kong Gateway with Helm:

 helm install kong kong/ingress -n kong --create-namespace 

Test connectivity to Kong

Kubernetes exposes the proxy through a Kubernetes service. Run the following commands to store the load balancer IP address in a variable named PROXY_IP:

Populate $PROXY_IP for future commands:

 export PROXY_IP=$(kubectl get svc --namespace kong kong-gateway-proxy -o jsonpath='{.status.loadBalancer.ingress[0].ip}')
 echo $PROXY_IP

Ensure that you can call the proxy IP:

 curl -i $PROXY_IP

The results should look like this:

 HTTP/1.1 404 Not Found
 Content-Type: application/json; charset=utf-8
 Connection: keep-alive
 Content-Length: 48
 X-Kong-Response-Latency: 0
 Server: kong/3.0.0
  
 {"message":"no Route matched with those values"}

Create a Kubernetes service

Create a Kubernetes service setup a httpbin service in the cluster and proxy it.

$ kubectl apply -f https://raw.githubusercontent.com/Kong/kubernetes-ingress-controller/v3.0.0/deploy/manifests/httpbin.yaml

The results should look like this:

service/httpbin created
deployment.apps/httpbin created

Setup Ingress rules

Expose the service outside the Kubernetes cluster by defining Ingress rules.

 echo '
 apiVersion: networking.k8s.io/v1
 kind: Ingress
 metadata:
   name: demo
   annotations:
     konghq.com/strip-path: "true"
 spec:
   ingressClassName: kong
   rules:
   - http:
       paths:
       - path: /test
         pathType: Prefix
         backend:
           service:
             name: httpbin
             port:
               number: 80
 ' | kubectl apply -f -

The results should look like this:

 ingress.networking.k8s.io/demo created

Test these endpoints.

 curl -i $PROXY_IP/test/status/200

The results should look like this:

 HTTP/1.1 200 OK
 Content-Type: text/html; charset=utf-8
 Content-Length: 0
 Connection: keep-alive
 Server: gunicorn/19.9.0
 Access-Control-Allow-Origin: *
 Access-Control-Allow-Credentials: true
 X-Kong-Upstream-Latency: 982
 X-Kong-Proxy-Latency: 2
 Via: kong/3.3.1

Observe that the headers and you can see that Kong has proxied the request correctly.

Setup passive health checking

All health checks are done at Service-level and not Ingress-level. To configure Kong to short-circuit requests to a Pod if it throws 3 consecutive errors, add a KongIngress resource.

echo "apiVersion: configuration.konghq.com/v1
kind: KongIngress
metadata:
    name: demo-health-checking
upstream:
  healthchecks:
    passive:
      healthy:
        successes: 3
      unhealthy:
        http_failures: 3" | kubectl apply -f -

The results should look like this:

kongingress.configuration.konghq.com/demo-health-checking created

Associate the KongIngress resource with httpbin service.

 $ kubectl patch svc httpbin -p '{"metadata":{"annotations":{"konghq.com/override":"demo-health-checking"}}}'

The results should look like this:

 service/httpbin patched

Test the Ingress rule by sending 2 requests that represent a failure from upstream and then send a request for 200. The requests with /status/500 simulate a failure from upstream. Send two requests with staus/500.

 $ curl -i $PROXY_IP/test/status/500
 $ curl -i $PROXY_IP/test/status/500

The results should look like this:

 HTTP/1.1 500 INTERNAL SERVER ERROR
 Content-Type: text/html; charset=utf-8
 Content-Length: 0
 Connection: keep-alive
 Server: gunicorn/19.9.0
 Access-Control-Allow-Origin: *
 Access-Control-Allow-Credentials: true
 X-Kong-Upstream-Latency: 2
 X-Kong-Proxy-Latency: 0
 Via: kong/3.1.1

Send the third request with staus/200

 $ curl -i $PROXY_IP/test/status/200

The results should look like this:

 HTTP/1.1 200 OK
 Content-Type: text/html; charset=utf-8
 Content-Length: 0
 Connection: keep-alive
 Server: gunicorn/19.9.0
 Access-Control-Allow-Origin: *
 Access-Control-Allow-Credentials: true
 X-Kong-Upstream-Latency: 2
 X-Kong-Proxy-Latency: 0
 Via: kong/3.1.1

Kong has not short-circuited because there were only two failures.

Send 3 requests to open the circuit, and then send a normal request. Send two requests with staus/500.

 $ curl -i $PROXY_IP/test/status/500
 $ curl -i $PROXY_IP/test/status/500
 $ curl -i $PROXY_IP/test/status/500

The results should look like this:

 HTTP/1.1 500 INTERNAL SERVER ERROR
 Content-Type: text/html; charset=utf-8
 Content-Length: 0
 Connection: keep-alive
 Server: gunicorn/19.9.0
 Access-Control-Allow-Origin: *
 Access-Control-Allow-Credentials: true
 X-Kong-Upstream-Latency: 2
 X-Kong-Proxy-Latency: 0
 Via: kong/3.1.1

Send the fourth request with staus/200

 $ curl -i $PROXY_IP/test/status/200

The results should look like this:

 HTTP/1.1 503 Service Temporarily Unavailable
 Content-Type: application/json; charset=utf-8
 Connection: keep-alive
 Content-Length: 62
 X-Kong-Response-Latency: 1
 Server: kong/3.3.1
    
 {
   "message":"failure to get a peer from the ring-balancer"
 }%                  

Kong returns a 503, indicating that the service is unavailable. Because there is only one Pod of httpbin service running in the cluster, and that is throwing errors, Kong does not proxy anymore requests.

There are a few options:

Delete the current httpbin Pod; Kong then sends proxy requests to the new Pod that comes in its place.
Scale the httpbin deployment; Kong then sends proxy requests to the new Pods and leave the short-circuited Pod out of the loop.
Manually change the Pod health status in Kong using Kong’s Admin API.

These options highlight the fact that once a circuit is opened because of errors, there is no way for Kong to close the circuit again.

This is a feature which some services might need, after a Pod starts throwing errors, manual intervention is necessary so that a Pod can again handle requests. To get around this, you can use active health-check, where each instance of Kong actively probes Pods to check if they are healthy.

Setup active health checking

Update the KongIngress resource to use active health-checks.

echo "apiVersion: configuration.konghq.com/v1
kind: KongIngress
metadata:
    name: demo-health-checking
upstream:
  healthchecks:
    active:
      healthy:
        interval: 5
        successes: 3
      http_path: /status/200
      type: http
      unhealthy:
        http_failures: 1
        interval: 5
    passive:
      healthy:
        successes: 3
      unhealthy:
        http_failures: 3" | kubectl apply -f -

The results should look like this:

kongingress.configuration.konghq.com/demo-health-checking created

This configures Kong to actively probe /status/200 every 5 seconds. If a Pod is unhealthy from Kong’s perspective, 3 successful probes changes the status of the Pod to healthy and Kong again starts to forward requests to that Pod. Wait 15 seconds for the pod to be marked as healthy before continuing.

Test the Ingress rule.

 $ curl -i $PROXY_IP/test/status/200

The results should look like this:

 HTTP/1.1 200 OK
 Content-Type: text/html; charset=utf-8
 Content-Length: 0
 Connection: keep-alive
 Server: gunicorn/19.9.0
 Access-Control-Allow-Origin: *
 Access-Control-Allow-Credentials: true
 X-Kong-Upstream-Latency: 2
 X-Kong-Proxy-Latency: 0
 Via: kong/3.1.1

Trip the circuit again by sending three requests that returns the status 500 from httpbin.

$ curl -i $PROXY_IP/test/status/500
$ curl -i $PROXY_IP/test/status/500
$ curl -i $PROXY_IP/test/status/500

When you send the requests, it fails for about 15 seconds, the duration for active health checks to re-classify the httpbin Pod as healthy again.

$ curl -i $PROXY_IP/test/status/200

The results should look like this:

HTTP/1.1 503 Service Temporarily Unavailable
Content-Type: application/json; charset=utf-8
Connection: keep-alive
Content-Length: 62
X-Kong-Response-Latency: 1
Server: kong/3.3.1
    
{
  "message":"failure to get a peer from the ring-balancer"
}%                  

Send the requests after 15 seconds or so.

$ curl -i $PROXY_IP/test/status/200

The results should look like this:

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 0
Connection: keep-alive
Server: gunicorn/19.9.0
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
X-Kong-Upstream-Latency: 2
X-Kong-Proxy-Latency: 0
Via: kong/3.1.1

Read more about health-checks and circuit breaker in Kong’s documentation.