Web server is down - Error Code 521

[gunavardhan.ganji]

Hi,
I am facing ‘Web server is down - Error code 521’ issue for my domain.

I have a GKE cluster and I have installed istio service mesh on top of it.

I have created a new edge certificate which allows *..com and I have created a secret in my cluster’s istio ingress gateway namespace and created a gateway which allows https port for my domain

apiVersion: networking.istio.io/v1beta1
kind: Gateway
metadata:  
  name: test-gateway
  namespace: admin
spec:
  selector:
    istio: ingress
  servers:  
  - port:
      number: 443
      name: https-istiotest
      protocol: HTTPS
    tls:
      mode: SIMPLE
      credentialName: <secret-name>
    hosts:
    - istiotest.<mydomain>.com

I have created an origin pool pointing to my istio ingress gateway external IP and created a health monitor which hits health service on my cluster on HTTPS (443) port. The health check for my origin pool is all healthy

Now, I have created a new load balancer with istiotest..com and connected the origin pool created above.

When I try to hit the service istiotest.<mydomain>.com/platform/health it gives my 521 (web server down) error. I am not sure where I am going wrong.

Troubleshooting I have done:

1. I have followed this document and allowed all the Cloudflare IPs - https://www.cloudflare.com/en-gb/ips/](https://www.cloudflare.com/en-gb/ips/ - Didn’t help
2. Followed this document and troubleshooting this error -https://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors/#error-521-web-server-is-down- This didn’t work as well

Note: platform is my api which has up and running in my cluster)

Can someone help me on this?