<p>I need to configure Ingress Nginx on azure k8s, and my question is if is possible to have ingress configured in one namespace et. ingress-nginx and some serivces in other namespace eg. resources?
My files looks like so:</p>

<pre><code># ingress-nginx.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-ingress-controller
  namespace: ingress-nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: ingress-nginx
  template:
    metadata:
      labels:
        app: ingress-nginx
      annotations:
        prometheus.io/port: '10254'
        prometheus.io/scrape: 'true' 
    spec:
      containers:
        - name: nginx-ingress-controller
          image: quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.12.0
          args:
            - /nginx-ingress-controller
            - --default-backend-service=$(POD_NAMESPACE)/default-http-backend
            - --configmap=$(POD_NAMESPACE)/nginx-configuration
            - --tcp-services-configmap=$(POD_NAMESPACE)/tcp-services
            - --udp-services-configmap=$(POD_NAMESPACE)/udp-services
            - --annotations-prefix=nginx.ingress.kubernetes.io
            - --publish-service=$(POD_NAMESPACE)/ingress-nginx
          env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
          ports:
          - name: http
            containerPort: 80
          - name: https
            containerPort: 443
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          readinessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
</code></pre>

<pre><code># configmap.yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: nginx-configuration
  namespace: ingress-nginx
  labels:
    app: ingress-nginx
---
kind: ConfigMap
apiVersion: v1
metadata:
  name: tcp-services
  namespace: ingress-nginx
---
kind: ConfigMap
apiVersion: v1
metadata:
  name: udp-services
  namespace: ingress-nginx
---
# default-backend.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: default-http-backend
  labels:
    app: default-http-backend
  namespace: ingress-nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: default-http-backend
  template:
    metadata:
      labels:
        app: default-http-backend
    spec:
      terminationGracePeriodSeconds: 60
      containers:
      - name: default-http-backend
        # Any image is permissible as long as:
        # 1. It serves a 404 page at /
        # 2. It serves 200 on a /healthz endpoint
        image: gcr.io/google_containers/defaultbackend:1.4
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 30
          timeoutSeconds: 5
        ports:
        - containerPort: 8080
        resources:
          limits:
            cpu: 10m
            memory: 20Mi
          requests:
            cpu: 10m
            memory: 20Mi
---
apiVersion: v1
kind: Service
metadata:
  name: default-http-backend
  namespace: ingress-nginx
  labels:
    app: default-http-backend
spec:
  ports:
  - port: 80
    targetPort: 8080
  selector:
    app: default-http-backend

</code></pre>

<pre><code>kind: Service
apiVersion: v1
metadata:
  name: ingress-nginx
  namespace: ingress-nginx
  labels:
    app: ingress-nginx
spec:
  externalTrafficPolicy: Local
  type: LoadBalancer
  selector:
    app: ingress-nginx
  ports:
  - name: http
    port: 80
    targetPort: http
  - name: https
    port: 443
    targetPort: https
</code></pre>

<pre><code>        # app-ingress.yaml
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: app-ingress
  namespace: ingress-nginx
  annotations:
    kubernetes.io/ingress.class: nginx
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  tls:
    - hosts:
      - api-sand.fake.com
  rules:
  - host: api-sand.fake.com
    http:
      paths:
      - backend:
          serviceName: api-sand
          servicePort: 80
        path: /

</code></pre>

<p>And then I have some app running in the <strong>resources namespace</strong>, and problem is that I am getting the following error </p>

<pre><code>error obtaining service endpoints: error getting service resources/api-sand from the cache: service resources/api-sand was not found

</code></pre>

<p>If I deploy api-sand in the same namespace where ingress is then this service works fine.</p>

<p>I would like to simplify the answer a bit for those who are relatively new to Kubernetes and its ingress options. There are 2 separate things that need to be present for ingress(es) to work:</p>
<ol>
<li><strong>Ingress Controller</strong>: a separate <code>DaemonSet</code> (a controller which runs on all nodes, including any future ones) along with a <code>Service</code> that can be used to utilize routing and proxying. It's based for example on NGINX which acts as the old-school reverse proxy receiving incoming traffic and forwarding it to HTTP(S) routes defined in the <code>Ingress</code> resources in point 2 below (distinguished by their different routes/URLs);</li>
<li><strong>Ingress rules</strong>: separate Kubernetes resources with <code>kind: Ingress</code>. Will only take effect if Ingress Controller is already <a href="https://kubernetes.io/docs/concepts/services-networking/ingress/#prerequisites" rel="noreferrer">deployed</a> on that node.</li>
</ol>
<p>While <strong>Ingress Controller can be deployed in any namespace</strong> it is usually deployed in a namespace separate from your app services (e.g. <code>ingress</code> or <code>kube-system</code>). It can see <code>Ingress</code> rules in all other namespaces and pick them up. However, each of the <strong>Ingress rules must reside in the namespace where the app that they configure reside.</strong></p>
<p>There are some workarounds for that, but this is the most common approach.</p>
