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Chapter 7. Managing metrics

You can collect metrics to monitor how cluster components and your own workloads are performing.

7.1. Understanding metrics
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In OpenShift Container Platform 4.11, cluster components are monitored by scraping metrics exposed through service endpoints. You can also configure metrics collection for user-defined projects.

You can define the metrics that you want to provide for your own workloads by using Prometheus client libraries at the application level.

In OpenShift Container Platform, metrics are exposed through an HTTP service endpoint under the /metrics canonical name. You can list all available metrics for a service by running a curl query against http://<endpoint>/metrics. For instance, you can expose a route to the prometheus-example-app example service and then run the following to view all of its available metrics: 

$ curl http://<example_app_endpoint>/metrics
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Example output

# HELP http_requests_total Count of all HTTP requests
# TYPE http_requests_total counter
http_requests_total{code="200",method="get"} 4
http_requests_total{code="404",method="get"} 2
# HELP version Version information about this binary
# TYPE version gauge
version{version="v0.1.0"} 1
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You can create a ServiceMonitor resource to scrape metrics from a service endpoint in a user-defined project. This assumes that your application uses a Prometheus client library to expose metrics to the /metrics canonical name.

This section describes how to deploy a sample service in a user-defined project and then create a ServiceMonitor resource that defines how that service should be monitored.

7.2.1. Deploying a sample service
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To test monitoring of a service in a user-defined project, you can deploy a sample service.

Procedure

  1. Create a YAML file for the service configuration. In this example, it is called prometheus-example-app.yaml.

  2. Add the following deployment and service configuration details to the file: 

    apiVersion: v1
kind: Namespace
metadata:
  name: ns1
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: prometheus-example-app
  name: prometheus-example-app
  namespace: ns1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: prometheus-example-app
  template:
    metadata:
      labels:
        app: prometheus-example-app
    spec:
      containers:
      - image: ghcr.io/rhobs/prometheus-example-app:0.4.2
        imagePullPolicy: IfNotPresent
        name: prometheus-example-app
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: prometheus-example-app
  name: prometheus-example-app
  namespace: ns1
spec:
  ports:
  - port: 8080
    protocol: TCP
    targetPort: 8080
    name: web
  selector:
    app: prometheus-example-app
  type: ClusterIP
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    This configuration deploys a service named prometheus-example-app in the user-defined ns1 project. This service exposes the custom version metric.

  3. Apply the configuration to the cluster: 

    $ oc apply -f prometheus-example-app.yaml
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    It takes some time to deploy the service.

  4. You can check that the pod is running: 

    $ oc -n ns1 get pod
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    Example output

    NAME                                      READY     STATUS    RESTARTS   AGE
prometheus-example-app-7857545cb7-sbgwq   1/1       Running   0          81m
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7.2.2. Specifying how a service is monitored
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To use the metrics exposed by your service, you must configure OpenShift Container Platform monitoring to scrape metrics from the /metrics endpoint. You can do this using a ServiceMonitor custom resource definition (CRD) that specifies how a service should be monitored, or a PodMonitor CRD that specifies how a pod should be monitored. The former requires a Service object, while the latter does not, allowing Prometheus to directly scrape metrics from the metrics endpoint exposed by a pod.

This procedure shows you how to create a ServiceMonitor resource for a service in a user-defined project.

Prerequisites

  • You have access to the cluster as a user with the cluster-admin cluster role or the monitoring-edit cluster role.
  • You have enabled monitoring for user-defined projects.

  • For this example, you have deployed the prometheus-example-app sample service in the ns1 project.

    Note

    The prometheus-example-app sample service does not support TLS authentication.

Procedure

  1. Create a YAML file for the ServiceMonitor resource configuration. In this example, the file is called example-app-service-monitor.yaml.

  2. Add the following ServiceMonitor resource configuration details: 

    apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  labels:
    k8s-app: prometheus-example-monitor
  name: prometheus-example-monitor
  namespace: ns1
spec:
  endpoints:
  - interval: 30s
    port: web
    scheme: http
  selector:
    matchLabels:
      app: prometheus-example-app
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    This defines a ServiceMonitor resource that scrapes the metrics exposed by the prometheus-example-app sample service, which includes the version metric.

    Note

    A ServiceMonitor resource in a user-defined namespace can only discover services in the same namespace. That is, the namespaceSelector field of the ServiceMonitor resource is always ignored.

  3. Apply the configuration to the cluster: 

    $ oc apply -f example-app-service-monitor.yaml
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    It takes some time to deploy the ServiceMonitor resource.

  4. You can check that the ServiceMonitor resource is running: 

    $ oc -n ns1 get servicemonitor
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    Example output

    NAME                         AGE
prometheus-example-monitor   81m
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7.3. Next steps
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