Understanding how to add custom metrics autoscalers - Automatically scaling pods with the Custom Metrics Autoscaler Operator | Nodes

Adding a custom metrics autoscaler to a workload
Additional resources

To add a custom metrics autoscaler, create a ScaledObject custom resource for a deployment, stateful set, or custom resource. Create a ScaledJob custom resource for a job.

You can create only one scaled object for each workload that you want to scale. Also, you cannot use a scaled object and the horizontal pod autoscaler (HPA) on the same workload.

Adding a custom metrics autoscaler to a workload

You can create a custom metrics autoscaler for a workload that is created by a deployment, StatefulSet, or custom resource object.

Prerequisites

The Custom Metrics Autoscaler Operator must be installed.

If you use a custom metrics autoscaler for scaling based on CPU or memory:

Your cluster administrator must have properly configured cluster metrics. You can use the oc describe PodMetrics <pod-name> command to determine if metrics are configured. If metrics are configured, the output appears similar to the following, with CPU and Memory displayed under Usage.

$ oc describe PodMetrics openshift-kube-scheduler-ip-10-0-135-131.ec2.internal

Example output

Name:         openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Namespace:    openshift-kube-scheduler
Labels:       <none>
Annotations:  <none>
API Version:  metrics.k8s.io/v1beta1
Containers:
  Name:  wait-for-host-port
  Usage:
    Memory:  0
  Name:      scheduler
  Usage:
    Cpu:     8m
    Memory:  45440Ki
Kind:        PodMetrics
Metadata:
  Creation Timestamp:  2019-05-23T18:47:56Z
  Self Link:           /apis/metrics.k8s.io/v1beta1/namespaces/openshift-kube-scheduler/pods/openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Timestamp:             2019-05-23T18:47:56Z
Window:                1m0s
Events:                <none>

The pods associated with the object you want to scale must include specified memory and CPU limits. For example:

Example pod spec

apiVersion: v1
kind: Pod
# ...
spec:
  containers:
  - name: app
    image: images.my-company.example/app:v4
    resources:
      limits:
        memory: "128Mi"
        cpu: "500m"
# ...

Procedure

Create a YAML file similar to the following. Only the name <2>, object name <4>, and object kind <5> are required:

Example scaled object

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  annotations:
    autoscaling.keda.sh/paused-replicas: "0" (1)
  name: scaledobject (2)
  namespace: my-namespace
spec:
  scaleTargetRef:
    apiVersion: apps/v1 (3)
    name: example-deployment (4)
    kind: deployment (5)
    envSourceContainerName: .spec.template.spec.containers[0] (6)
  cooldownPeriod:  200 (7)
  maxReplicaCount: 100 (8)
  minReplicaCount: 0 (9)
  metricsServer: (10)
    auditConfig:
      logFormat: "json"
      logOutputVolumeClaim: "persistentVolumeClaimName"
      policy:
        rules:
        - level: Metadata
        omitStages: "RequestReceived"
        omitManagedFields: false
      lifetime:
        maxAge: "2"
        maxBackup: "1"
        maxSize: "50"
  fallback: (11)
    failureThreshold: 3
    replicas: 6
  pollingInterval: 30 (12)
  advanced:
    restoreToOriginalReplicaCount: false (13)
    horizontalPodAutoscalerConfig:
      name: keda-hpa-scale-down (14)
      behavior: (15)
        scaleDown:
          stabilizationWindowSeconds: 300
          policies:
          - type: Percent
            value: 100
            periodSeconds: 15
  triggers:
  - type: prometheus (16)
    metadata:
      serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
      namespace: kedatest
      metricName: http_requests_total
      threshold: '5'
      query: sum(rate(http_requests_total{job="test-app"}[1m]))
      authModes: basic
    authenticationRef: (17)
      name: prom-triggerauthentication
      kind: TriggerAuthentication

1	Optional: Specifies that the Custom Metrics Autoscaler Operator is to scale the replicas to the specified value and stop autoscaling, as described in the "Pausing the custom metrics autoscaler for a workload" section.
2	Specifies a name for this custom metrics autoscaler.
3	Optional: Specifies the API version of the target resource. The default is `apps/v1`.
4	Specifies the name of the object that you want to scale.
5	Specifies the `kind` as `deployment`, `StatefulSet` or `CustomResource`.
6	Optional: Specifies the name of the container in the target resource, from which the custom metrics autoscaler gets environment variables holding secrets and so forth. The default is `.spec.template.spec.containers[0]`.
7	Optional. Specifies the period in seconds to wait after the last trigger is reported before scaling the deployment back to `0` if the `minReplicaCount` is set to `0`. The default is `300`.
8	Optional: Specifies the maximum number of replicas when scaling up. The default is `100`.
9	Optional: Specifies the minimum number of replicas when scaling down.
10	Optional: Specifies the parameters for audit logs. as described in the "Configuring audit logging" section.
11	Optional: Specifies the number of replicas to fall back to if a scaler fails to get metrics from the source for the number of times defined by the `failureThreshold` parameter. For more information on fallback behavior, see the KEDA documentation.
12	Optional: Specifies the interval in seconds to check each trigger on. The default is `30`.
13	Optional: Specifies whether to scale back the target resource to the original replica count after the scaled object is deleted. The default is `false`, which keeps the replica count as it is when the scaled object is deleted.
14	Optional: Specifies a name for the horizontal pod autoscaler. The default is `keda-hpa-{scaled-object-name}`.
15	Optional: Specifies a scaling policy to use to control the rate to scale pods up or down, as described in the "Scaling policies" section.
16	Specifies the trigger to use as the basis for scaling, as described in the "Understanding the custom metrics autoscaler triggers" section. This example uses OpenShift Dedicated monitoring.
17	Optional: Specifies a trigger authentication or a cluster trigger authentication. For more information, see Understanding the custom metrics autoscaler trigger authentication in the Additional resources section. Enter `TriggerAuthentication` to use a trigger authentication. This is the default. Enter `ClusterTriggerAuthentication` to use a cluster trigger authentication.

Create the custom metrics autoscaler by running the following command:
```
$ oc create -f <filename>.yaml
```

Verification

View the command output to verify that the custom metrics autoscaler was created:
```
$ oc get scaledobject <scaled_object_name>
```
Example output
```
NAME            SCALETARGETKIND      SCALETARGETNAME        MIN   MAX   TRIGGERS     AUTHENTICATION               READY   ACTIVE   FALLBACK   AGE
scaledobject    apps/v1.deployment   example-deployment     0     50    prometheus   prom-triggerauthentication   True    True     True       17s
```
Note the following fields in the output:
- TRIGGERS: Indicates the trigger, or scaler, that is being used.
- AUTHENTICATION: Indicates the name of any trigger authentication being used.
- READY: Indicates whether the scaled object is ready to start scaling:
  
  If True, the scaled object is ready.
  
  If False, the scaled object is not ready because of a problem in one or more of the objects you created.
- ACTIVE: Indicates whether scaling is taking place:
  
  If True, scaling is taking place.
  
  If False, scaling is not taking place because there are no metrics or there is a problem in one or more of the objects you created.
- FALLBACK: Indicates whether the custom metrics autoscaler is able to get metrics from the source
  
  If False, the custom metrics autoscaler is getting metrics.
  
  If True, the custom metrics autoscaler is getting metrics because there are no metrics or there is a problem in one or more of the objects you created.

Additional resources

Understanding custom metrics autoscaler trigger authentications