Ingress controller name for the ingress class - kubernetes

Question

I am setting up my ingress controller, ingress class and ingress to expose a service outside the cluster. This is fresh cluster setup.
I have setup the nginx-ingress controller using
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v0.41.0/deploy/static/provider/baremetal/deploy.yaml
The next step based on my understanding is to create the ingress class https://v1-18.docs.kubernetes.io/docs/concepts/services-networking/ingress/#ingress-class
apiVersion: networking.k8s.io/v1beta1
kind: IngressClass
metadata:
name: external-lb
spec:
controller: example.com/ingress-controller
parameters:
apiGroup: k8s.example.com/v1alpha
kind: IngressParameters
name: external-lb
How did they get the name of the controller example.com/ingress-controller?

Answer 1

I have run multiple scenarios with IngressClass, Ingress and Nginx Ingress Controller.
Scenario 1
IngressClass with custom name
Nginx Ingress Controller with default --ingress-class value which is nginx
Ingress using ingressClassName same as IngressClass name
Output: Response 404
Scenario 2
IngressClass with custom name
Nginx Ingress Controller with owningress-class ingress-test
Ingress using ingressClassName same as IngressClass name
Output: Response 404
Scenario 3
IngressClass with test name
Nginx Ingress Controller --ingress-class with value test
Ingress using test in ingressClassName
Output: Proper response
Senario 4
IngressClass with nginx name
Nginx Ingress Controller --ingress-class with value nginx
Ingress using nginx in ingressClassName
Output: Proper response
Conclusion
First of all, please keep in mind that there are 3 types of Nginx. Open Source Nginx Ingress Controller, you are probably using it. Nginx Incorporaton (nginx inc) and Nginx Incorporaton Plus.
In one of the scenarios, when I have used spec.controller: nginx.org/ingress-controller with Nginx Ingress Controller with argument --ingress-class=nginx, in Nginx Ingress Controller pod you will see entry which is pointing to k8s.io/ingress-nginx.
To reproduce this behavior, you will need to deploy IngressClass with specific controller and then deploy nginx.
apiVersion: networking.k8s.io/v1beta1
kind: IngressClass
metadata:
name: nginx
spec:
controller: nginx.org/ingress-controller
After deploying Nginx Ingress Controller, controller pod will be in CrashLoopBackOff state. In logs you will find entry:
E1118 15:42:19.008911 8 main.go:134] Invalid IngressClass (Spec.Controller) value "nginx.org/ingress-controller". Should be "k8s.io/ingress-nginx"
It works only when IngressClass name is set to nginx.
I would say that nginx.org/ingress-controller is for Nginx Incorporated and k8s.io/ingress-nginx for Open Source Nginx Ingress.
If custom value is used for --ingress-class argument in the controller Deployment manifest, presence or absence of IngressClass object with the same name doesn't made any difference in, how the cluster works, if only you keep Ingress spec.ingressClass value the same with controller argument. Moreover, if it's present, IngressClass spec.controller can have any value that match the required pattern "domain like" and that didn't affect Ingress workflow behavior on my cluster at all.
In addition, Ingress works fine if I put the correct value of the ingress-class either to spec.ingressClass property or to metadata.annotation.kubernetes.io/ingress.class accordingly. It gives an error like the following if you try to put both values to the same Ingres object:
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
name: test-ingress
annotations:
kubernetes.io/ingress.class: nginx
spec:
ingressClassName: nginx
The Ingress "test-ingress" is invalid: annotations.kubernetes.io/ingress.class: Invalid value: "nginx": can not be set when the class field is also set
Please keep in mind it was tested only for Nginx Ingress Controlle. If you would like to use IngressClass with other Ingress Controllers like Traefik or Ambasador, you would check their release notes.

Answer 2

You will create the IngressClass as part of the Installation with Manifests steps (Step 3 here). That will create an IngressClass that looks like:
apiVersion: networking.k8s.io/v1beta1
kind: IngressClass
metadata:
name: nginx
# annotations:
# ingressclass.kubernetes.io/is-default-class: "true"
spec:
controller: nginx.org/ingress-controller
Then, to configure an Ingress resource to be consumed by nginx, just specify ingressClassName: nginx in the Ingress spec, as shown here, and pasted again below:
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
name: cafe-ingress
spec:
ingressClassName: nginx
tls:
- hosts:
- cafe.example.com
secretName: cafe-secret
rules:
- host: cafe.example.com
. . .