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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

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

7.2. Setting up metrics collection for user-defined projects
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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

    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

    It takes some time to deploy the service.

  4. You can check that the pod is running: 

    $ oc -n ns1 get pod

    Example output

    NAME                                      READY     STATUS    RESTARTS   AGE
prometheus-example-app-7857545cb7-sbgwq   1/1       Running   0          81m

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

    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

    It takes some time to deploy the 

    ServiceMonitor
    resource.

  4. You can check that the 

    ServiceMonitor
    resource is running: 

    $ oc -n ns1 get servicemonitor

    Example output

    NAME                         AGE
prometheus-example-monitor   81m

7.3. Next steps
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