Route nginx to services in different namespaces - nginx

Question

We have a Kubernetes cluster with an nginx controller.
We are using this nginx controller to route different paths to different services. Though,
when a service is on a different namespace, I cannot figure out how to redirect to it.
This is the nginx configuration
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: gateway-ingress
annotations:
kubernetes.io/ingress.class: "nginx"
kubernetes.io/tls-acme: 'true'
nginx.ingress.kubernetes.io/proxy-body-size: "0"
nginx.ingress.kubernetes.io/proxy-read-timeout: "600"
nginx.ingress.kubernetes.io/proxy-send-timeout: "600"
nginx.ingress.kubernetes.io/enable-cors: "true"
nginx.ingress.kubernetes.io/cors-allow-methods: "*"
nginx.ingress.kubernetes.io/cors-allow-headers: "*"
nginx.ingress.kubernetes.io/cors-allow-origin: "*"
nginx.ingress.kubernetes.io/service-upstream: "true"
spec:
rules:
- host: MY_BACKEND.MY_DOMAIN.com
http:
paths:
- pathType: Prefix
path: "/"
backend:
service:
name: my-backend
port:
number: 3001
- host: MY_FRONTEND.MY_DOMAIN.com
http:
paths:
- pathType: Prefix
path: "/"
backend:
service:
name: my-frontend
port:
number: 3000
...
The above snippet works perfectly, but it is worth to mention that both services my-backend and my-frontend are running on default namespace.
We have then deployed a Jenkins instance on namespace jenkins. My first attempty was to simply add
- host: MY_JENKINS.MY_DOMAIN.com
http:
paths:
- pathType: Prefix
path: "/"
backend:
service:
name: jenkins-service
port:
number: 8080
Though when browsing on MY_JENKINS.MY_DOMAIN.com I get a 503 Service Temporary Unavailable. Could it be because it is running on a different namespace? Namely jenkins?
Normally in order to connect on different namespaces I just use the standard service.namespace. Though here when trying I get a standard console error/warning
The Ingress "gateway-ingress" is invalid: spec.rules[16].http.paths[0].backend.service.name: Invalid value: "WHATEVER_VALUE_WRITTEN": a DNS-1035 label must consist of lower case alphanumeric characters or '-', start with an alphabetic character, and end with an alphanumeric character (e.g. 'my-name', or 'abc-123', regex used for validation is '[a-z]([-a-z0-9]*[a-z0-9])?')
I tried: service.namespace, namespace.service, namespace/service, service/namespace. All the attempts and up on the same error message.
How can I instruct nginx-controller to connect to a service that is in a specific namespace?

Answer 1

You can reach a service from another namespace with: <service>.<namespace>; by bypassing the service you can also reach other pods by their ip address (even in another namespace).
But afaik all ingress controllers (also nginx) per default do not allow multi-namespace ingress out of security reasons.
For nginx you can configure ingress across multiple namespaces with a master/minion approach. You have to add the nginx.org/mergeable-ingress-type-annotation to your Ingress resources.
A master processes configuration on the host and minions provide the ingress resources.
Find more info here: https://docs.nginx.com/nginx-ingress-controller/configuration/ingress-resources/cross-namespace-configuration/
And here:
https://github.com/nginxinc/kubernetes-ingress/tree/v2.2.1/examples/mergeable-ingress-types