Explain Openshift resource manifest

[Chetan_Tiwary_]

Explain this openshift resource manifest

apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: hpa-resource-metrics-memory
  namespace: default
spec:
...
  minReplicas: 20
...
  behavior:
    scaleDown:
      stabilizationWindowSeconds: 300
      policies:
      - type: Pods
        value: 4
        periodSeconds: 30
      - type: Percent
        value: 10
        periodSeconds: 60
      selectPolicy: Max
    scaleUp:
      selectPolicy: Disabled

[Kent-Kamau]

The provided resource manifest is for a HorizontalPodAutoscaler (HPA) which automatically scales the number of pods in a deployment or replica set based on observed resource usage or other metrics.

This HorizontalPodAutoscaler is set to:

1. Minimum Replicas: Always maintain at least 20 pods.
2. Scale Down Behavior: After scaling down, wait for 5 minutes before considering another scale-down event.
3. Limit scale-down actions to a maximum of 4 pods within 30 seconds or 10% of the total pods within 60 seconds, whichever is greater.
4. The Max scaling policy ensures that the largest scale-down value will be applied.
5. Scale Up Behavior: Scaling up is disabled for this HPA, meaning no new pods will be added even if resource usage increases.

[juicylemon]

This configuration helps manage the number of replicas in response to changing workload demands while preventing rapid scaling oscillations.
Minimum 20 replicas running, scalling down is gradually with 10% cut down every minute or 4 pods every 30 seconds, which ever is bigger.
Scaling up targeting utilization without specific policy. 

[mcapileibm]

HorizontalPodAutoscaler (HPA) in OpenShift manages pod scaling based on % resource usage.
ensures at least 20 pods are always running (minReplicas: 20).
Scaling down : It can remove up to 4 pods every 30 seconds or 10% of pods every 60 seconds.
Scaling up is disabled, meaning new pods won’t be added automatically.

[walid-cnj]

Is that an old manifest?   The latest stable version of the Horizontal Pod Autoscaler (HPA) API is:  apiVersion: autoscaling/v2 was introduced in Kubernetes 1.23 and became stable (GA) in Kubernetes 1.26.

Other than what others already said, I present my concerns, what is not there instead of what is there!!

Some Concerns:
1- With scaling up disabled, the system can't automatically handle increased load
   scaleUp:  selectPolicy: Disabled

2- The minimum of 20 replicas might be resource-intensive if not needed, haven't seen it in my 6+ years of K8s operations?!

3- The 5-minute stabilization window might be too long for most workloads

4- Having two scale-down policies introduces confusion as well might lead to aggressive scaling in some scenarios

Thoughts:

Update to the right/latest API version for HPA.

Doesn't want automatic scaling up (possibly handled by other mechanisms?!)
Needs careful, controlled scaling down?!
Requires high availability (minimum 20 pods)?!

[MonazahAzhar]

Its horizontal pod autosacalling configuration file which has details given below:
setting the repicas minimum to 20 

setting the scalling behaviour for scaling down by 4 pod (10%) every 30 seconds with stability of 5 minuts.
its not gona scale up as per this configuration

[pramod188]

- This HPA creates the scaledown policy,
- This HPA maintains 20 minimum replicas. Even if load decreases, openshift will not scale below 20.
- The first policy (Pods) allows at most 4 replicas to be scaled down in 30 seconds. The second policy (Percent) allows atmost 10 percent of
the current replicas to be scaled down in 60 seconds. This will repart in each iterations.

- In this example there are two policies defined and it specifies Policy to `selectPolicy: Max`    The Max policy allows the highest amount of change. For lowest amount of the chnage Min can be used.

- The default value for Policy is Max.