I have a backend service named – backend-service.
The pod of this service does the host based routing, like when run below from the pod –

curl --location 'http://localhost:9900/api/foo' 
--header 'Host: foo.example.com' 
--header 'Content-Type: application/json' 
--data-raw '{
   "foo": "bar" 
}'

This gives 200 status.

Now I have a ingress rule with host bar.example.com which has this backend service configured.
when I am accessing bar.example.com with header ‘Host: foo.example.com’, nginx gives 404 error.

Command used –

curl --location 'http://bar.example.com/api/foo' 
--header 'Host: foo.example.com' 
--header 'Content-Type: application/json' 
--data-raw '{
   "foo": "bar" 
}'

Below are my ingress annotations –

    nginx.ingress.kubernetes.io/affinity: cookie
    nginx.ingress.kubernetes.io/session-cookie-expires: "172800"
    nginx.ingress.kubernetes.io/session-cookie-max-age: "172800"
    nginx.ingress.kubernetes.io/session-cookie-name: SESSION

ingress-nginx-controller configmap –

  allow-snippet-annotations: "true"
  enable-access-log-for-default-backend: "true"
  enable-underscores-in-headers: "true"
  large-client-header-buffers: 4 100k
  proxy-real-ip-cidr: 10.1.2.3/23,10.1.2.4/24
  use-forwarded-headers: "true"

Seems nginx is not preserving the host header passed from client.
What could be issue here ?