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exposing-prometheus-and-alertmanager.md

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Note: Starting with v0.39.0, Prometheus Operator requires use of Kubernetes v1.16.x and up.

Exposing Prometheus and Alertmanager

The Prometheus Operator takes care of operating Prometheus and Alertmanagers clusters. Kubernetes provides several ways to expose these clusters to the outside world. This document outlines best practices and caveats for exposing Prometheus and Alertmanager clusters.

NodePort

The easiest way to expose Prometheus or Alertmanager is to use a Service of type NodePort.

Create a simple Prometheus object with one replica:

apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  name: main
spec:
  resources:
    requests:
      memory: 400Mi

All Prometheus Pods are labeled with prometheus: <prometheus-name>. If the Prometheus object's name is main, the selector is prometheus: main. This means that the respective manifest for the Service must define the selector as prometheus: main.

apiVersion: v1
kind: Service
metadata:
  name: prometheus-main
spec:
  type: NodePort
  ports:
  - name: web
    nodePort: 30900
    port: 9090
    protocol: TCP
    targetPort: web
  selector:
    prometheus: main

After creating a Service with the above manifest, the web UI of Prometheus will be accessible by browsing to any of the worker nodes using http://<node-ip>:30900/.

Exposing the Alertmanager works in the same fashion, with the selector alertmanager: <alertmanager-name>.

apiVersion: monitoring.coreos.com/v1
kind: Alertmanager
metadata:
  name: main
spec:
  replicas: 3
  resources:
    requests:
      memory: 400Mi

And the Service.

apiVersion: v1
kind: Service
metadata:
  name: alertmanager-main
spec:
  type: NodePort
  ports:
  - name: web
    nodePort: 30903
    port: 9093
    protocol: TCP
    targetPort: web
  selector:
    alertmanager: main

The Alertmanager web UI will be available at http://<node-ip>:30903/.

Kubernetes API

The Kubernetes API has a feature of forwarding requests from the API to a cluster internal Service. The general URL scheme to access these is:

http(s)://control-plane-host/api/v1/proxy/namespaces/<namespace>/services/<service-name>:<port-name-or-number>/

For ease of use, use kubectl proxy. It proxies requests from a local address to the Kubernetes API server and handles authentication.

To be able to do so, create a Service of type ClusterIP:

apiVersion: v1
kind: Service
metadata:
  name: prometheus-main
spec:
  type: ClusterIP
  ports:
  - name: web
    port: 9090
    protocol: TCP
    targetPort: web
  selector:
    prometheus: main

Prometheus and Alertmanager must be configured with the full URL at which they will be exposed. Therefore the Prometheus manifest requires an entry for externalUrl:

apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  name: main
spec:
  externalUrl: http://127.0.0.1:8001/api/v1/proxy/namespaces/default/services/prometheus-main:web/
  resources:
    requests:
      memory: 400Mi

Note the externalUrl uses the host 127.0.0.1:8001, which is how kubectl proxy exposes the Kubernetes API by default.

Once the Prometheus Pods are running they are reachable under the specified externalUrl.

The Alertmanager object's manifest follows the same rules:

apiVersion: monitoring.coreos.com/v1
kind: Alertmanager
metadata:
  name: main
spec:
  replicas: 3
  externalUrl: http://127.0.0.1:8001/api/v1/proxy/namespaces/default/services/alertmanager-main:web/
  resources:
    requests:
      memory: 400Mi

And the respective Service:

apiVersion: v1
kind: Service
metadata:
  name: alertmanager-main
spec:
  type: ClusterIP
  ports:
  - name: web
    port: 9093
    protocol: TCP
    targetPort: web
  selector:
    alertmanager: main

Then it will be available under http://127.0.0.1:8001/api/v1/proxy/namespaces/default/services/alertmanager-main:web/.

Note the URL for the Service uses the host 127.0.0.1:8001, which is how kubectl proxy exposes the Kubernetes API by default.

Ingress

Exposing the Prometheus or Alertmanager web UI through an Ingress object requires a running Ingress controller. For more information, see the Kubernetes documentation on Ingress.

This example was tested with the NGINX Ingress Controller. For a quick-start for running the NGINX Ingress Controller follow the instructions in the NGINX Ingress installation guide.

Be certain to evaluate available Ingress controllers for the specifics of your production environment. The NGINX Ingress Controller may or may not be suitable. Consider other solutions, like HA Proxy, Traefik, GCE, or AWS.

WARNING: If your Ingress is exposed to the internet, everyone can have full access on your resources. It's strongly recommend to enable an external authentication or whitelisting IP address.

An Ingress object also requires a Service to be set up, as the requests are routed from the Ingress endpoint to the internal Service.

apiVersion: v1
kind: Service
metadata:
  name: prometheus-main
spec:
  type: ClusterIP
  ports:
  - name: web
    port: 9090
    protocol: TCP
    targetPort: web
  selector:
    prometheus: main
---
apiVersion: v1
kind: Service
metadata:
  name: alertmanager-main
spec:
  type: ClusterIP
  ports:
  - name: web
    port: 9093
    protocol: TCP
    targetPort: web
  selector:
    alertmanager: main

A corresponding Ingress object would be:

apiVersion: extensions/v1
kind: Ingress
metadata:
  name: monitoring
  annotations:
    ingress.kubernetes.io/whitelist-source-range: 10.0.0.0/16 # change this range to admin IPs
    nginx.ingress.kubernetes.io/rewrite-target: /$2
spec:
  rules:
  - http:
      paths:
      - backend:
          serviceName: prometheus-main
          servicePort: 9090
        path: /prometheus(/|$)(.*)
      - backend:
          serviceName: alertmanager-main
          servicePort: 9093
        path: /alertmanager(/|$)(.*)

Finally, the Prometheus and Alertmanager objects must be created, specifying the externalUrl at which they will be found.

apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  name: main
spec:
  externalUrl: http://monitoring.my.systems/prometheus
  resources:
    requests:
      memory: 400Mi
---
apiVersion: monitoring.coreos.com/v1
kind: Alertmanager
metadata:
  name: main
spec:
  replicas: 3
  externalUrl: http://monitoring.my.systems/alertmanager
  resources:
    requests:
      memory: 400Mi

Note the path /prometheus at the end of the externalUrl, as specified in the Ingress object.