How to manage incoming traffic for multiple instances of the same app with isolated namespaces and unique subdomains using an Ingress Controller?

General Discussions
1

How can I use an Ingress Controller in K8S to manage traffic for multiple instances of the same application with isolated namespaces and unique subdomains for each instance? I need each instance to have two services (backend and frontend) accessible via their respective subdomains. However, the Ingress Controller cannot access other namespaces, creating an issue in managing traffic. I’ve considered placing the Ingress Controller in the kube-system namespace, but I’m not sure if this is a good practice. I’ve also heard about ISTIO, but I’m unsure if it can solve my problem. Any suggestions or ideas on how to resolve this issue are appreciated.

Here is an example of the NGINX Ingress Controller that I have started to use (so that you have an idea of what I want to do):

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress
  annotations:
    nginx.ingress.kubernetes.io/ingress.class: nginx
spec:
  ingressClassName: nginx
  rules:
    - host: sub-01.my-domain.com
      http:
        paths:
          - path: /api/
            pathType: Prefix
            backend:
              service:
                name: sub-01-backend-service
                port:
                  number: 30000
          - path: /
            pathType: Prefix
            backend:
              service:
                name: sub-01-frontend-service
                port:
                  number: 80
    - host: sub-02.my-domain.com
      http:
        paths:
          - path: /api/
            pathType: Prefix
            backend:
              service:
                name: sub-02-backend-service
                port:
                  number: 30000
          - path: /
            pathType: Prefix
            backend:
              service:
                name: sub-02-frontend-service
                port:
                  number: 80

Thanks in advance for your help.

2

The Ingress API can not cross namespaces, but the implementation of the ingress controller can. The nginx controller, last I looked, was a “merging” implementation - a single pool of nginx instances run, and all Ingress resources (in all namespaces) are merged into one big config.

So you should be able to drop an Ingress into each namespace.