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+# Prometheus operator
+
+The purpose of this document is to explain how to setup [Prometheus operator](https://github.com/coreos/prometheus-operator) for Knative observability. It also describes how to scrape metrics endpoints using service monitors.
+
+## Cluster setup
+
+Create a kubernetes cluster as mentioned [here](https://knative.dev/docs/install/knative-with-gke/#creating-a-kubernetes-cluster).
+
+> Note: A GKE cluster is used, but any other cluster type can be used as well.
+
+Export the cluster properties:
+
+```bash
+export CLUSTER_NAME="YOUR_CLUSTER_NAME" \
+export CLUSTER_PROJECT="YOUR_CLUSTER_PROJECT" \
+export CLUSTER_ZONE="YOUR_CLUSTER_ZONE"
+```
+
+Create a GKE cluster:
+
+```bash
+gcloud beta container --project "${CLUSTER_PROJECT}" clusters create ${CLUSTER_NAME} \
+  --addons=HorizontalPodAutoscaling,HttpLoadBalancing,Istio \
+  --machine-type=n1-standard-4 \
+  --cluster-version=latest --zone=${CLUSTER_ZONE} \
+  --enable-stackdriver-kubernetes --enable-ip-alias \
+  --enable-autoscaling --min-nodes=1 --max-nodes=10 \
+  --enable-autorepair \
+  --scopes cloud-platform
+```
+
+Grant the cluster-admin permissions:
+
+```bash
+kubectl create clusterrolebinding cluster-admin-binding \
+  --clusterrole=cluster-admin \
+  --user=$(gcloud config get-value core/account)
+```
+
+## Knative setup
+
+### Install Knative [Serving](https://github.com/knative/serving/blob/master/DEVELOPMENT.md#deploy-knative-serving) and [Eventing](https://github.com/knative/eventing/blob/master/DEVELOPMENT.md#starting-eventing-controller)
+
+> Note: Skip the installation of the monitoring components of Knative serving.
+
+### Configure monitoring for Knative Serving and Eventing
+
+```bash
+# configure monitoring for Eventing
+cat << EOF | kubectl apply -f -
+apiVersion: v1
+data:
+  metrics.backend-destination: prometheus
+kind: ConfigMap
+metadata:
+  labels:
+    eventing.knative.dev/release: devel
+  name: config-observability
+  namespace: knative-eventing
+EOF
+
+# configure monitoring for Serving
+cat << EOF | kubectl apply -f -
+apiVersion: v1
+data:
+  metrics.backend-destination: prometheus
+kind: ConfigMap
+metadata:
+  labels:
+    serving.knative.dev/release: devel
+  name: config-observability
+  namespace: knative-serving
+EOF
+```
+
+## Prometheus operator setup
+
+### Create the `knative-monitoring` namespace
+
+```bash
+cat << EOF | kubectl apply -f -
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: knative-monitoring
+  labels:
+    monitoring.knative.dev/release: devel
+EOF
+```
+
+### Install the Prometheus operator
+
+```bash
+cat << EOF | kubectl apply -f -
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  labels:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+    app.kubernetes.io/version: v0.33.0
+  name: prometheus-operator
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: prometheus-operator
+subjects:
+- kind: ServiceAccount
+  name: prometheus-operator
+  namespace: knative-monitoring
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  labels:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+    app.kubernetes.io/version: v0.33.0
+  name: prometheus-operator
+rules:
+- apiGroups:
+  - apiextensions.k8s.io
+  resources:
+  - customresourcedefinitions
+  verbs:
+  - '*'
+- apiGroups:
+  - monitoring.coreos.com
+  resources:
+  - alertmanagers
+  - prometheuses
+  - prometheuses/finalizers
+  - alertmanagers/finalizers
+  - servicemonitors
+  - podmonitors
+  - prometheusrules
+  verbs:
+  - '*'
+- apiGroups:
+  - apps
+  resources:
+  - statefulsets
+  verbs:
+  - '*'
+- apiGroups:
+  - '*'
+  resources:
+  - configmaps
+  - secrets
+  verbs:
+  - '*'
+- apiGroups:
+  - '*'
+  resources:
+  - pods
+  verbs:
+  - '*'
+- apiGroups:
+  - '*'
+  resources:
+  - services
+  - services/finalizers
+  - endpoints
+  verbs:
+  - '*'
+- apiGroups:
+  - '*'
+  resources:
+  - nodes
+  verbs:
+  - '*'
+- apiGroups:
+  - '*'
+  resources:
+  - namespaces
+  verbs:
+  - '*'
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+    app.kubernetes.io/version: v0.33.0
+  name: prometheus-operator
+  namespace: knative-monitoring
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app.kubernetes.io/component: controller
+      app.kubernetes.io/name: prometheus-operator
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/component: controller
+        app.kubernetes.io/name: prometheus-operator
+        app.kubernetes.io/version: v0.33.0
+    spec:
+      containers:
+      - args:
+        - --kubelet-service=kube-system/kubelet
+        - --logtostderr=true
+        - --config-reloader-image=quay.io/coreos/configmap-reload:v0.0.1
+        - --prometheus-config-reloader=quay.io/coreos/prometheus-config-reloader:v0.33.0
+        image: quay.io/coreos/prometheus-operator:v0.33.0
+        name: prometheus-operator
+        ports:
+        - containerPort: 8080
+          name: http
+        resources:
+          limits:
+            cpu: 200m
+            memory: 200Mi
+          requests:
+            cpu: 100m
+            memory: 100Mi
+        securityContext:
+          allowPrivilegeEscalation: false
+      nodeSelector:
+        beta.kubernetes.io/os: linux
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 65534
+      serviceAccountName: prometheus-operator
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  labels:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+    app.kubernetes.io/version: v0.33.0
+  name: prometheus-operator
+  namespace: knative-monitoring
+---
+apiVersion: v1
+kind: Service
+metadata:
+  labels:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+    app.kubernetes.io/version: v0.33.0
+  name: prometheus-operator
+  namespace: knative-monitoring
+spec:
+  clusterIP: None
+  ports:
+  - name: http
+    port: 8080
+    targetPort: http
+  selector:
+    app.kubernetes.io/component: controller
+    app.kubernetes.io/name: prometheus-operator
+EOF
+```
+
+### Wait until the Prometheus operator is up and running
+
+```bash
+kubectl get pods --namespace knative-monitoring --selector='app.kubernetes.io/component=controller,app.kubernetes.io/name=prometheus-operator' --watch
+```
+
+### Create an instance from the Prometheus CR
+
+```bash
+cat << EOF | kubectl apply -f -
+apiVersion: monitoring.coreos.com/v1
+kind: Prometheus
+metadata:
+  labels:
+    app: prometheus
+    prometheus: monitoring
+  name: monitoring
+  namespace: knative-monitoring
+spec:
+  baseImage: quay.io/prometheus/prometheus
+  logLevel: info
+  paused: false
+  replicas: 1
+  resources:
+    limits:
+      memory: 1Gi
+    requests:
+      memory: 512Mi
+  retention: 2h
+  routePrefix: /
+  ruleSelector:
+    matchLabels:
+      prometheus: monitoring
+  securityContext:
+    fsGroup: 2000
+    runAsNonRoot: true
+    runAsUser: 1000
+  serviceAccountName: prometheus-operator
+  serviceMonitorSelector:
+    matchLabels:
+      prometheus: monitoring
+  storage:
+    volumeClaimTemplate:
+      spec:
+        accessModes:
+        - ReadWriteOnce
+        resources:
+          requests:
+            storage: 4Gi
+EOF
+```
+
+### Wait until Prometheus is up and running
+
+```bash
+kubectl get pod --namespace knative-monitoring prometheus-monitoring-0 --watch
+```
+
+## Verification
+
+### NatssChannel setup
+
+Install NATS Streaming server:
+
+```bash
+kubectl create namespace natss; \
+kubectl apply --namespace natss -f https://raw.githubusercontent.com/knative/eventing/v0.7.0/contrib/natss/config/broker/natss.yaml
+```
+
+Install NatssChannel:
+
+```bash
+cd ${GOPATH}/src/knative.dev/eventing-contrib/natss/config; \
+git checkout master; \
+ko apply -f .
+```
+
+Add the monitoring port to the **natss-ch-dispatcher** service:
+
+```bash
+# edit the natss-ch-dispatcher service
+kubectl edit service --namespace knative-eventing natss-ch-dispatcher
+
+# add the following config
+spec:
+  ports:
+  - name: http
+    port: 80
+    protocol: TCP
+    targetPort: 8080
+  - name: metrics-port
+    port: 9090
+    protocol: TCP
+    targetPort: 9090
+```
+
+### Create a service monitor for the NatssChannel dispatcher
+
+```bash
+cat << EOF | kubectl apply -f -
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: natss-ch-dispatcher-metrics
+  namespace: knative-monitoring
+  labels:
+    contrib.eventing.knative.dev/release: devel
+    messaging.knative.dev/channel: natss-channel
+    messaging.knative.dev/role: dispatcher
+    prometheus: monitoring
+spec:
+  type: ClusterIP
+  ports:
+  - name: metrics-port
+    port: 9090
+  selector:
+    messaging.knative.dev/channel: natss-channel
+    messaging.knative.dev/role: dispatcher
+---
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: natss-ch-dispatcher-metrics
+  namespace: knative-monitoring
+  labels:
+    contrib.eventing.knative.dev/release: devel
+    messaging.knative.dev/channel: natss-channel
+    messaging.knative.dev/role: dispatcher
+    prometheus: monitoring
+spec:
+  selector:
+    matchLabels:
+      messaging.knative.dev/channel: natss-channel
+      messaging.knative.dev/role: dispatcher
+  endpoints:
+  - port: metrics-port
+    interval: 10s
+  namespaceSelector:
+    any: true
+EOF
+```
+
+### Check Prometheus targets
+
+Do a port-forward to access Prometheus targets endpoint:
+
+```bash
+kubectl port-forward --namespace knative-monitoring \
+   $(kubectl get pods --namespace knative-monitoring \
+   --selector=app=prometheus --output=jsonpath="{.items[0].metadata.name}") \
+   9090
+```
+
+Access [http://localhost:9090/targets](http://localhost:9090/targets), in a few seconds, the **knative-monitoring/natss-ch-dispatcher-metrics** job should be up.
+
+## Cleanup
+
+```bash
+gcloud container clusters delete ${CLUSTER_NAME} --zone ${CLUSTER_ZONE}
+```