For a quick test of horizontal autoscaling of an NginX deployment, we need the following ingredients:
- a metrics server installation to be able to measure the POD’s CPU
- an nginx deployment with a CPU reservation
- an auto scaler configuration
- a process that causes high CPU
This can be tested on: https://killercoda.com/playgrounds/scenario/kubernetes
Install Metrics (quick&insecure way)
curl -s -L https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml | sed 's_\(--cert-dir=/tmp\)_\1\n\ \ \ \ \ \ \ \ - --kubelet-insecure-tls_g' | k apply -f -
Create an NginX Deployment…
…with CPU resource request of 0.1
k create deploy nginx --image=nginx --dry-run=client -o yaml | sed 's_\(resources: \){}_resources:\n\ \ \ \ \ \ \ \ \ \ requests:\n\ \ \ \ \ \ \ \ \ \ \ \ cpu: 0.1_' > nginx.deploy.yaml;
k apply -f nginx.deploy.yamlCreate a horizontal Autoscaler
kubectl autoscale deployment nginx --cpu-percent=50 --min=1 --max=4
Run a high CPU Process
k exec -it deploy/nginx -- bash -c 'while true; do echo -n . >/dev/null; done'
Scaling up Result:
k get hpa --watch NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE nginx Deployment/nginx 0%/50% 1 4 1 51s nginx Deployment/nginx 721%/50% 1 4 1 60s nginx Deployment/nginx 942%/50% 1 4 4 75s nginx Deployment/nginx 228%/50% 1 4 4 90s
Scaling down Result
After stopping the while loop, we see:
k get hpa --watch NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE nginx Deployment/nginx 0%/50% 1 4 4 6m47s nginx Deployment/nginx 0%/50% 1 4 4 8m15s nginx Deployment/nginx 0%/50% 1 4 1 8m30s
Appendix: A. 1: Next Generation (v2) Autoscaling with Default Behavior
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
creationTimestamp: null
name: nginx
spec:
maxReplicas: 4
minReplicas: 1
behavior:
scaleDown:
stabilizationWindowSeconds: 300
policies:
- type: Percent
value: 100
periodSeconds: 15
scaleUp:
stabilizationWindowSeconds: 0
policies:
- type: Percent
value: 100
periodSeconds: 15
- type: Pods
value: 4
periodSeconds: 15
selectPolicy: Max
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: nginx
Appendix: A. 2: Next Generation (v2) Autoscaling with Custom Behavior
The target here is:
- scale down quickly, if there is no high CPU anymore (stabilizationWindowSeconds set to 0)
- scale up one by one every 60 seconds: Pods value 1 and periodSeconds 60
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
creationTimestamp: null
name: nginx
spec:
maxReplicas: 4
minReplicas: 1
behavior:
scaleDown:
stabilizationWindowSeconds: 0
policies:
- type: Percent
value: 100
periodSeconds: 15
scaleUp:
stabilizationWindowSeconds: 0
policies:
- type: Pods
value: 1
periodSeconds: 60
selectPolicy: Max
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: nginx
we can see that the number of replicas rises one by one from 1 to 4, while the load is high, and the number of replicas goes down quickly if the CPU is below its threshold:
controlplane $ k get hpa --watch NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE nginx Deployment/nginx 0%/80% 1 4 1 32m nginx Deployment/nginx 517%/80% 1 4 1 32m nginx Deployment/nginx 816%/80% 1 4 2 33m nginx Deployment/nginx 414%/80% 1 4 2 33m nginx Deployment/nginx 428%/80% 1 4 2 33m nginx Deployment/nginx 428%/80% 1 4 2 34m nginx Deployment/nginx 419%/80% 1 4 3 34m nginx Deployment/nginx 274%/80% 1 4 3 34m nginx Deployment/nginx 275%/80% 1 4 3 35m nginx Deployment/nginx 279%/80% 1 4 4 35m nginx Deployment/nginx 236%/80% 1 4 4 35m nginx Deployment/nginx 214%/80% 1 4 4 35m nginx Deployment/nginx 204%/80% 1 4 4 36m nginx Deployment/nginx 134%/80% 1 4 4 36m nginx Deployment/nginx 0%/80% 1 4 4 36m nginx Deployment/nginx 0%/80% 1 4 1 36m
More Information:
- Concept Overview
- HorizontalPodAutoscaler Walkthrough
- Official Reference Documentation
- Reason why we need a metrics server: https://stackoverflow.com/questions/44736101/kubectl-get-hpa-targetsunknow
- HowTo install a metrics server: https://stackoverflow.com/questions/52694238/kubectl-top-node-error-metrics-not-available-yet-using-metrics-server-as-he
- Using the insecure option of metrics server: https://stackoverflow.com/questions/73880030/x509-cannot-validate-certificate-for-host-ip-because-it-doesnt-contain-any-i
Next Generation Autoscaling with Behavior Control
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