Chapter 2. Exposing custom application metrics for autoscaling

Procedure

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

2. 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
   ---

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3. 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>>)'
   ---

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   1

   Specifies the chosen metric to be the number of HTTP requests.

   2

   Specifies the frequency for the metric.

4. 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
   ---

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5. Show the Prometheus Adapter image to use:

   $ kubectl get -n openshift-monitoring deploy/prometheus-adapter -o jsonpath="{..image}"
   quay.io/openshift-release-dev/ocp-v4.2-art-dev@sha256:76db3c86554ad7f581ba33844d6a6ebc891236f7db64f2d290c3135ba81c264c

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6. 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-v4.2-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: {}

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   1

   image: openshift-release-dev/ocp-v4.2-art-dev specifies the Prometheus Adapter image found in the previous step.

7. Apply the configuration file to the cluster:

   $ oc apply -f deploy.yaml

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8. Now the application’s metrics are exposed and can be used to configure horizontal pod autoscaling.