Adding nginx gateway fabric monitoring (#520)

base-kustomize/prometheus-nginx-gateway/nginx-gateway-monitor.yaml

@@ -0,0 +1,17 @@
+apiVersion: monitoring.coreos.com/v1
+kind: PodMonitor
+metadata:
+  name: nginx-gateway-fabric
+  namespace: prometheus
+  labels:
+    app.kubernetes.io/name: nginx-gateway-fabric
+spec:
+  namespaceSelector:
+    matchNames:
+      - nginx-gateway
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: nginx-gateway-fabric
+  podMetricsEndpoints:
+    - port: metrics
+      interval: 15s

docs/prometheus-nginx-gateway.md

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+# NGINX Gateway Fabric Monitoring
+
+NGINX Gateway Fabric exposes a lot of important metrics about the gateway. We simply
+create a pod monitor to pull these metrics into Prometheus.
+
+
+## Installation
+
+``` shell
+kubectl apply -f /etc/genestack/kustomize/prometheus-nginx-gateway/
+```
+
+!!! success
+    If the installation is successful, you should see metrics with `nginx_gateway_fabric_*` in Prometheus.