conf(ingress-nginx): Enable prometheus scraping

Create the ServiceMonitor to enable scraping within prometheus for the
ingress-nginx metrics.

Author: ssoriche

platform/ingress-nginx/kustomization.yaml

@@ -4,6 +4,7 @@ kind: Kustomization
 resources:
   - https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v1.10.1/deploy/static/provider/do/deploy.yaml
   - service.yaml
+  - servicemonitor.yaml
 patchesStrategicMerge:
   - |-
     apiVersion: v1

platform/ingress-nginx/servicemonitor.yaml

@@ -0,0 +1,22 @@
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: ingress-nginx-controller
+  namespace: ingress-nginx
+  labels:
+    app.kubernetes.io/name: ingress-nginx
+    app.kubernetes.io/part-of: ingress-nginx
+    release: prometheus
+spec:
+  endpoints:
+    - port: metrics
+      interval: 30s
+      path: /metrics
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: ingress-nginx
+      app.kubernetes.io/instance: ingress-nginx
+      app.kubernetes.io/component: controller
+  namespaceSelector:
+    matchNames:
+      - ingress-nginx