[appmesh-gateway] Support passing in custom namespaceSelector for VirtualGateway

[hscheib]

Is your feature request related to a problem?
Yes, two versions of the same chart cant be used in two namespaces on the same cluster.

I created two namespaces (apps and service) and have the appmesh.k8s.aws/sidecarInjectorWebhook: enabled annotation on both of them for app mesh side car injection. I have installed appmesh-controller : 1.2.1. I then helm install the appmesh-gateway : 0.1.5 helm chart to both namespaces. The problem happens now when I try to apply a Kind: GatewayRoute to the cluster. I get:

admission webhook "mgatewayroute.appmesh.k8s.aws" denied the request: found multiple matching virtualGateways for namespace: service, expecting 1 but found 2: appmesh-gateway,service-gateway-appmesh-gateway

Is your feature request related to a specific Helm chart, if yes mention name of the chart?
Yes, appmesh-gateway

Describe the solution you'd like
I would like to be able to pass in my own namespace selector value instead of always relying on the hardcoded namespaceSelector that exists today. The annotation appmesh.k8s.aws/sidecarInjectorWebhook: enabled is required for the sidecar injects and is not unique across namespaces.

ie:

values:
    appmesh:
        gateway:
            namespaceSelector:
                gateway: apps-gateway

Describe alternatives you've considered
I was able to get around this by updating my values of the charts to

values:
    appmesh:
        gateway: false

and then manually creating my own Kind: VirtualGateway with a namespaceSelector I pick that is unique per namespace

ie:

---
apiVersion: appmesh.k8s.aws/v1beta2
kind: Mesh
metadata:
  name: stage
spec:
  namespaceSelector:
    matchLabels:
      mesh: stage
---
apiVersion: v1
kind: Namespace
metadata:
  labels:
    mesh: stage
    gateway: apps-gateway
    appmesh.k8s.aws/sidecarInjectorWebhook: enabled
  name: apps
---
apiVersion: v1
kind: Namespace
metadata:
  labels:
    mesh: stage
    gateway: service-gateway
    appmesh.k8s.aws/sidecarInjectorWebhook: enabled
  name: service
---
apiVersion: appmesh.k8s.aws/v1beta2
kind: VirtualGateway
metadata:
  name: service-gateway
  namespace: service
spec:
  namespaceSelector:
    matchLabels:
      gateway: service-gateway
  podSelector:
    matchLabels:
      app.kubernetes.io/name: service-gateway-appmesh-gateway
  listeners:
    - portMapping:
        port: 8088
        protocol: http
  logging:
    accessLog:
      file:
        path: "/dev/stdout"
---
apiVersion: appmesh.k8s.aws/v1beta2
kind: VirtualGateway
metadata:
  name: apps-gateway
  namespace: apps
spec:
  namespaceSelector:
    matchLabels:
      gateway: apps-gateway
  podSelector:
    matchLabels:
      app.kubernetes.io/name: appmesh-gateway
  listeners:
    - portMapping:
        port: 8088
        protocol: http
  logging:
    accessLog:
      file:
        path: "/dev/stdout"

Creating GatewayRoutes were then successful. This request will simplify creating multiple VirtualGateways across namespaces when using appmesh-gateway helm chart.