Exposing custom application metrics for autoscaling | Monitoring

Exposing custom application metrics for horizontal pod 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

Make sure you have a custom Prometheus instance installed. In this example, it is presumed that Prometheus was installed in the default namespace.
Make sure you configured monitoring for your application. In this example, it is presumed that the application and the service monitor for it were installed in the default namespace.

Procedure

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

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

kind: serviceAccount
apiVersion: v1
metadata:
  name: custom-metrics-apiserver
  namespace: default
---
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: default
---
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: default
---
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: default
---
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
---

Add configuration for the custom metrics for prometheus-adapter:

apiVersion: v1
kind: ConfigMap
metadata:
  name: adapter-config
  namespace: default
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.

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

apiVersion: v1
kind: service
metadata:
  annotations:
    service.alpha.openshift.io/serving-cert-secret-name: prometheus-adapter-tls
  labels:
    name: prometheus-adapter
  name: prometheus-adapter
  namespace: default
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: default
  group: custom.metrics.k8s.io
  version: v1beta1
  insecureSkipTLSVerify: true
  groupPriorityMinimum: 100
  versionPriority: 100
---

Show the Prometheus Adapter image to use:

$ kubectl get -n openshift-monitoring deploy/prometheus-adapter -o jsonpath="{..image}"
quay.io/openshift-release-dev/ocp-v4.3-art-dev@sha256:76db3c86554ad7f581ba33844d6a6ebc891236f7db64f2d290c3135ba81c264c

Add configuration for deploying prometheus-adapter:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: prometheus-adapter
  name: prometheus-adapter
  namespace: default
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: openshift-release-dev/ocp-v4.3-art-dev (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	`image: openshift-release-dev/ocp-v4.3-art-dev` specifies the Prometheus Adapter image found in the previous step.

Apply the configuration file to the cluster:
```
$ oc apply -f deploy.yaml
```
Now the application’s metrics are exposed and can be used to configure horizontal pod autoscaling.

Additional resources

See the horizontal pod autoscaling documentation.
See the Kubernetes documentation on horizontal pod autoscaler.