Kubernetes - How ingress routing works

2
votes

I saw some example where the Kubernetes cluster is installed with ingress controller and then the ingress class is added with annotations and host as below.

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
 annotations:
    kubernetes.io/ingress.class: nginx

spec:
 rules:
   - host: testsvc.k8s.privatecloud.com
     http:

I am not sure which service is installed and which IP is configured with the DNS "k8s.privatecloud.com" so as to route requests? How the DNS routing "k8s.privatecloud.com" routes requests to Kubernetes cluster? How the ingress to kubernetes bridging works?

Also, There could be many services configured with the hosts rule like,

testsvc.k8s.privatecloud.com
testsvc1.k8s.privatecloud.com
testsvc2.k8s.privatecloud.com

How the subdomain routing works here when we hit the service testsvc.k8s.privatecloud.com or testsvc1.k8s.privatecloud.com ...

Thanks

2
kuberneteskubernetes-ingress

2 Answers

1
votes

The DNS for all the hostnames in your given example (e.g. testsvc.k8s.privatecloud.com) would point to the machine or load-balancer through which traffic will reach the Ingress controller's nginx, as is described in the kuberetes Ingress documentation

Subdomain routing is traditionally done via "virtual-hosting", sometimes called "v-host-ing", and the nginx ingress uses the HTTP Host: header to know which backend service should receive that traffic. Some Ingress controllers are able to use SNI for that same trick over https.

1
votes

In addition to @Matthew L Daniel answer. The kubernetes Ingress works as a proxy between external network and your cluster. The behavior of the ingress is explained in the object ingress. For example: 

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: test
  annotations:
    ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: foo.bar.com
    http:
      paths:
      - path: /foo
        backend:
          serviceName: s1
          servicePort: 80
      - path: /bar
        backend:
          serviceName: s2
          servicePort: 80

Above it`s explained how to route traffic between 2 backends s1 and s2. Ingress does not hold any information about services except its name and port, every time it needs more details it would need to be requested from the api-server.