I m bit new to Kubernetes and was going over "Ingress". after reading the k8 docs and googling , I summarised the following. Can somebody confirm/correct my understanding:

To understand Ingress, I divided it into 2 sections :

Cloud Infrastructure:

In this, there is in-built ingress controller which runs in the master node(but we can't see it when running kubectl get pods -n all). To configure , first create ur Deployment Pods and expose them through services (Service Type=NodePort must). Also, make sure to create default-backend-service. Then create ingress rules as follows:

kind: Ingress
metadata:
  name: app-ingress
spec:
  backend:
   serviceName: default-svc
   servicePort: 80
  rules:
  - host: api.foo.com
    http:
      paths:
      - path: /v1/
        backend:
          serviceName: api-svc-v1
          servicePort: 80
      - path: /v2/
        backend:
          serviceName: api-svc-v2
          servicePort: 80

Once you apply the ingress rules to the API server, ingress controller listens to the API and updates the /etc/nginx.conf. Also, after few mins, nginx controller creates an external Load balancer with an IP(lets say LB_IP)

now to test: from your browser, enter http://api.foo.com/(or(http://api.foo.com/(or) http://) which will redirect to default service and http://api.foo.com/v1(or(http://api.foo.com/v1(or) http:///v1) which will redirect it service api-svc-v1

Question:

1. how can I see /etc/nginx files since the ingress controller pod is not visible.

2. During the time, ingress rules are applied and an external LB_IP is getting created, does all the DNS servers of all registrars are updated with DNS entry "api.foo.com "

In-house kubernetes deployment using kubeadm:

In this, there is no external ingress controller and you need to install it manually. To configure, first create ur deployment pods and expose them through service (make sure that service Type=NodePort). Also, make sure to create default-backend-service.Create Ingress controller using the below yaml file:

spec: 
  containers: 
    - 
      args: 
        - /nginx-ingress-controller
        - "--default-backend-service=\\$(POD_NAMESPACE)/default-backend"
      image: "gcr.io/google_containers/nginx-ingress-controller:0.8.3"
      imagePullPolicy: Always
      livenessProbe: 
        httpGet: 
          path: /healthz
          port: 10254
          scheme: HTTP
        initialDelaySeconds: 10
        timeoutSeconds: 5
      name: nginx-ingress-controller
      readinessProbe: 
        httpGet: 
          path: /healthz
          port: 10254
          scheme: HTTP

we can see the ingress controller running in node3 using "kubectl get pods" and login to this pod, we can see /etc/nginx/nginx.conf

Now create the ingress rules as follows:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    ingress.kubernetes.io/rewrite-target: /
  name: app-ingress
spec:
  rules:
  - host: testabc.com
    http:
      paths:
      - backend:
          serviceName: appsvc1
          servicePort: 80
        path: /app1
      - backend:
          serviceName: appsvc2
          servicePort: 80
        path: /app2

Once you apply the ingress rules to the API server, ingress controller listens to the API and updates the /etc/nginx.conf. But note that there is no Load balancer created . Instead when you do "kubectl get ingress", you get Host=testabc.com and IP=127.0.0.1. Now to expose this ingress-controller outside, I need to create a service with type=NodePort or type=Loadbalancer

kind: Service
metadata:    
  name: nginx-ingress    
spec:
  type: NodePort
  ports:
    - port: 80
      nodePort: 33200
      name: http
    selector:
    app: nginx-ingress-lb

After this, we will get an external IP(if type=Loadbalancer)

now to test: from your browser, enter http://testabc.com/(or(http://testabc.com/(or) http://) which will redirect to default service and http://testabc.com/v1(or(http://testabc.com/v1(or) http:///v1) which will redirect it service api-svc-v1

Question:

3.if the ingress-controller pod is running in node3, how it can listen to ingress api which is running in node1