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Exposing custom application metrics for autoscaling

You can export custom application metrics for the horizontal pod autoscaler.

Prometheus Adapter is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Exposing custom application metrics for horizontal pod autoscaling

You can use the prometheus-adapter resource to expose custom application metrics for the horizontal pod autoscaler.

Prerequisites

  • You have a custom Prometheus instance installed as a Prometheus pod managed by a deployment or StatefulSet object but not by a Prometheus custom resource (CR).

  • You have installed the custom Prometheus instance in a user-defined custom-prometheus project.

    Custom Prometheus instances and the Prometheus Operator installed through Operator Lifecycle Manager (OLM) are not compatible with user-defined monitoring if it is enabled. Therefore, custom Prometheus instances that are installed as a Prometheus custom resource (CR) managed by the OLM Prometheus Operator are not supported in OKD.

  • You have deployed an application and a service in a user-defined project. In this example, it is presumed that the application and its service monitor were installed in a user-defined custom-prometheus project.

  • You have installed the OpenShift CLI (oc).

Procedure

  1. Create a YAML file for your configuration. In this example, the file is called deploy.yaml.

  2. Add configuration details for creating the service account, roles, and role bindings for prometheus-adapter:

    kind: ServiceAccount
apiVersion: v1
metadata:
  name: custom-metrics-apiserver
  namespace: custom-prometheus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: custom-metrics-server-resources
rules:
- apiGroups:
  - custom.metrics.k8s.io
  resources: ["*"]
  verbs: ["*"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: custom-metrics-resource-reader
rules:
- apiGroups:
  - ""
  resources:
  - namespaces
  - pods
  - services
  verbs:
  - get
  - list
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: custom-metrics:system:auth-delegator
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:auth-delegator
subjects:
- kind: ServiceAccount
  name: custom-metrics-apiserver
  namespace: custom-prometheus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: custom-metrics-auth-reader
  namespace: kube-system
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: extension-apiserver-authentication-reader
subjects:
- kind: ServiceAccount
  name: custom-metrics-apiserver
  namespace: custom-prometheus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: custom-metrics-resource-reader
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: custom-metrics-resource-reader
subjects:
- kind: ServiceAccount
  name: custom-metrics-apiserver
  namespace: custom-prometheus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: hpa-controller-custom-metrics
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: custom-metrics-server-resources
subjects:
- kind: ServiceAccount
  name: horizontal-pod-autoscaler
  namespace: kube-system
---

  3. Add configuration details for the custom metrics for prometheus-adapter:

    apiVersion: v1
kind: ConfigMap
metadata:
  name: adapter-config
  namespace: custom-prometheus
data:
  config.yaml: |
    rules:
    - seriesQuery: 'http_requests_total{namespace!="",pod!=""}' (1)
      resources:
        overrides:
          namespace: {resource: "namespace"}
          pod: {resource: "pod"}
          service: {resource: "service"}
      name:
        matches: "^(.*)_total"
        as: "${1}_per_second" (2)
      metricsQuery: 'sum(rate(<<.Series>>{<<.LabelMatchers>>}[2m])) by (<<.GroupBy>>)'
---
    1 Specifies the chosen metric to be the number of HTTP requests.
    2 Specifies the frequency for the metric.

  4. Add configuration details for registering prometheus-adapter as an API service:

    apiVersion: v1
kind: Service
metadata:
  annotations:
    service.beta.openshift.io/serving-cert-secret-name: prometheus-adapter-tls
  labels:
    name: prometheus-adapter
  name: prometheus-adapter
  namespace: custom-prometheus
spec:
  ports:
  - name: https
    port: 443
    targetPort: 6443
  selector:
    app: prometheus-adapter
  type: ClusterIP
---
apiVersion: apiregistration.k8s.io/v1beta1
kind: APIService
metadata:
  name: v1beta1.custom.metrics.k8s.io
spec:
  service:
    name: prometheus-adapter
    namespace: custom-prometheus
  group: custom.metrics.k8s.io
  version: v1beta1
  insecureSkipTLSVerify: true
  groupPriorityMinimum: 100
  versionPriority: 100
---

  5. List the Prometheus Adapter image:

    $ oc get -n openshift-monitoring deploy/prometheus-adapter -o jsonpath="{..image}"

  6. Add configuration details for deploying prometheus-adapter:

    apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: prometheus-adapter
  name: prometheus-adapter
  namespace: custom-prometheus
spec:
  replicas: 1
  selector:
    matchLabels:
      app: prometheus-adapter
  template:
    metadata:
      labels:
        app: prometheus-adapter
      name: prometheus-adapter
    spec:
      serviceAccountName: custom-metrics-apiserver
      containers:
      - name: prometheus-adapter
        image: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:a46915a206cd7d97f240687c618dd59e8848fcc3a0f51e281f3384153a12c3e0 (1)
        args:
        - --secure-port=6443
        - --tls-cert-file=/var/run/serving-cert/tls.crt
        - --tls-private-key-file=/var/run/serving-cert/tls.key
        - --logtostderr=true
        - --prometheus-url=http://prometheus-operated.default.svc:9090/
        - --metrics-relist-interval=1m
        - --v=4
        - --config=/etc/adapter/config.yaml
        ports:
        - containerPort: 6443
        volumeMounts:
        - mountPath: /var/run/serving-cert
          name: volume-serving-cert
          readOnly: true
        - mountPath: /etc/adapter/
          name: config
          readOnly: true
        - mountPath: /tmp
          name: tmp-vol
      volumes:
      - name: volume-serving-cert
        secret:
          secretName: prometheus-adapter-tls
      - name: config
        configMap:
          name: adapter-config
      - name: tmp-vol
        emptyDir: {}
    1 Specifies the Prometheus Adapter image found in the previous step.

  7. Apply the configuration to the cluster:

    $ oc apply -f deploy.yaml
    Example output
    serviceaccount/custom-metrics-apiserver created
clusterrole.rbac.authorization.k8s.io/custom-metrics-server-resources created
clusterrole.rbac.authorization.k8s.io/custom-metrics-resource-reader created
clusterrolebinding.rbac.authorization.k8s.io/custom-metrics:system:auth-delegator created
rolebinding.rbac.authorization.k8s.io/custom-metrics-auth-reader created
clusterrolebinding.rbac.authorization.k8s.io/custom-metrics-resource-reader created
clusterrolebinding.rbac.authorization.k8s.io/hpa-controller-custom-metrics created
configmap/adapter-config created
service/prometheus-adapter created
apiservice.apiregistration.k8s.io/v1.custom.metrics.k8s.io created
deployment.apps/prometheus-adapter created

  8. Verify that the prometheus-adapter pod in your user-defined project is in a Running state. In this example the project is custom-prometheus:

    $ oc -n custom-prometheus get pods prometheus-adapter-<string>

  9. The metrics for the application are now exposed and they can be used to configure horizontal pod autoscaling.

Additional resources

Next steps