Published: Fri 08 September 2023
Updated: Fri 08 September 2023
By Hephzibah Pon Cellat Arulprakash
In k8s .
tags: k8s
This article discusses Horizontal Pod Autoscaling (HPA), one of the types of autoscaling in Kubernetes.
What is Horizontal Autoscaling
Horizontal autoscaling is based on the load in CPU and memory, you can scale up or down the number of pods automatically so that your application can better serve during high or low traffic hours eventually customers can have a seamless experience.
For this purpose, you would configure the minimum and maximum number of pods to be created based on metrics like CPU and memory.
There is a concept called vertical autoscaling where you add nodes to increase the infrastructure capacity in terms of CPU, RAM, storage, etc.,
How in Kubernetes
Deploying sample application using Kubernetes Deployment and Service
Consider below deployment and service definition yaml file php-apache.yaml.
apiVersion : apps / v1
kind : Deployment
metadata :
name : php - apache
spec :
selector :
matchLabels :
run : php - apache
template :
metadata :
labels :
run : php - apache
spec :
containers :
- name : php - apache
image : registry . k8s . io / hpa - example
ports :
- containerPort : 80
resources :
limits :
cpu : 500 m
requests :
cpu : 200 m
---
apiVersion : v1
kind : Service
metadata :
name : php - apache
labels :
run : php - apache
spec :
ports :
- port : 80
selector :
run : php - apache
Assuming you already have a k8s cluster setup, to create deployment and service resources,
$ kubectl apply -f php-apache.yaml
This would create a deployment and service as below. From the deployment, the replicaset is created and from the replicaset, pods are created. so we have a service, deployment, replicaset, and pod.
$ kubectl get all
NAME READY STATUS RESTARTS AGE
pod/php-apache-7495ff8f5b-gt8r8 1 /1 Running 0 4m29s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT( S) AGE
service/php-apache ClusterIP 10 .100.126.40 <none> 80 /TCP 4m29s
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/php-apache 1 /1 1 1 4m29s
NAME DESIRED CURRENT READY AGE
replicaset.apps/php-apache-7495ff8f5b 1 1 1 4m29s
To check if the sample application is working, as this service is of type Cluster-IP, we can either expose the service as NodePort so that it is accessible from the host machine, or we can ssh into the cluster and access via the Cluster-IP.
Testing Application Method 1 (optional)
Expose the service php-apache to a new service of type Nodeport so that it will be accessible from your local machine and outside of the Kubernetes cluster. You can now access the app from the local machine using the IP address of the cluster followed by the port exposed in NodePort.
$ kubectl expose service php-apache --port= 80 --target-port= 80 --name= php-apache-np --type= NodePort
service/php-apache-np exposed
$ kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT( S) AGE
php-apache ClusterIP 10 .100.126.40 <none> 80 /TCP 29m
php-apache-np NodePort 10 .102.48.181 <none> 80 :30708/TCP 4s
$ minikube ip
192 .168.49.2
$ curl http://192.168.49.2:30708
OK!
Testing Application Method 2 (optional)
To SSH into the cluster and check the PHP application, the below example assumes the cluster is created using Minikube.
$ minikube ssh
docker@minikube:~$
To check the application, use curl with the app IP address. The app IP address can be found in Cluster-IP from the service by executing kubectl get svc php-apache.
$ minikube ssh
docker@minikube:~$ curl http://10.100.126.40
OK!
Create Metrics Server
Download the latest release of the metrics server.
curl - LO https : // github . com / kubernetes - sigs / metrics - server / releases / latest / download / components . yaml
Add the lines hostNetwork: true and - --kubelet-insecure-tls in components.yaml.
template:
metadata:
labels:
k8s-app: metrics-server
spec:
hostNetwork: true
containers:
- args:
- --kubelet-insecure-tls
- --cert-dir=/tmp
- --secure-port=4443
Apply the components.yaml.
kubectl apply -f components.yaml
Check for the pods in the namespace kube-system.
$ kubectl get pod -n kube-system
NAME READY STATUS RESTARTS AGE
...
metrics-server-77d9b56856-qjxh7 1 /1 Running 0 3m32s
...
Check if it's installed properly by,
$ kubectl top nodes
NAME CPU( cores) CPU% MEMORY( bytes) MEMORY%
minikube 389m 19 % 901Mi 11 %
$ kubectl top pods
NAME CPU( cores) MEMORY( bytes)
php-apache-7495ff8f5b-gt8r8 1m 31Mi
If it is installed properly you will see the output about the CPU, and memory metrics as shown above.
Create the Horizontal Pod AutoScaler
Create a Horizontal Pod Autoscaler which would autoscale if the CPU usage goes beyond 50% with the minimum and maximum number of pods to be autoscaled.
$ kubectl autoscale deployment php-apache --cpu-percent= 50 --min= 1 --max= 10
View the HPA resource,
$ kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
php-apache Deployment/php-apache 0 %/50% 1 10 1 65m
As currently, the application has no load, the target is 0%. HPA gets this information from the metrics server installed previously.
Increase the Load
To increase the load we will be using the busybox image, which continuously accesses the application in a loop. In a new terminal,
$ kubectl run - i -- tty load - generator -- rm -- image = busybox : 1.28 -- restart = Never -- / bin / sh - c "while sleep 0.01; do wget -q -O- http://php-apache; done"
In the other terminal, after a while, you can see the target % is increased leading to autoscale out the deployment which affects the replicasets which in turn increases the number of pods to handle the load.
$ kubectl get all
NAME READY STATUS RESTARTS AGE
pod / load - generator 1 / 1 Running 0 105 s
pod / php - apache - 7495 ff8f5b - gfzhb 1 / 1 Running 0 68 s
pod / php - apache - 7495 ff8f5b - gt8r8 1 / 1 Running 1 ( 72 m ago ) 4 h
pod / php - apache - 7495 ff8f5b - j8fb9 1 / 1 Running 0 69 s
pod / php - apache - 7495 ff8f5b - p26g7 1 / 1 Running 0 53 s
pod / php - apache - 7495 ff8f5b - vhxt8 0 / 1 Pending 0 8 s
pod / php - apache - 7495 ff8f5b - wzlr4 1 / 1 Running 0 84 s
NAME TYPE CLUSTER - IP EXTERNAL - IP PORT ( S ) AGE
service / kubernetes ClusterIP 10.96 . 0.1 < none > 443 / TCP 4 h1m
service / php - apache ClusterIP 10.100 . 126.40 < none > 80 / TCP 4 h
service / php - apache - np NodePort 10.102 . 48.181 < none > 80 : 30708 / TCP 3 h31m
NAME READY UP - TO - DATE AVAILABLE AGE
deployment . apps / php - apache 5 / 6 6 5 4 h
NAME DESIRED CURRENT READY AGE
replicaset . apps / php - apache - 7495 ff8f5b 6 6 5 4 h
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
horizontalpodautoscaler . autoscaling / php - apache Deployment / php - apache 56 %/ 50 % 1 10 5 70 m
Now stop the load to the application by Ctrl+C in the terminal where busybox was run. After a few minutes, you can see the pods would have autoscaled down, decreasing the number of pods due to less or no traffic to the application.
$ kubectl get all
NAME READY STATUS RESTARTS AGE
pod/php-apache-7495ff8f5b-gt8r8 1 /1 Running 1 ( 78m ago) 4h7m
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT( S) AGE
service/kubernetes ClusterIP 10 .96.0.1 <none> 443 /TCP 4h7m
service/php-apache ClusterIP 10 .100.126.40 <none> 80 /TCP 4h7m
service/php-apache-np NodePort 10 .102.48.181 <none> 80 :30708/TCP 3h37m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/php-apache 1 /1 1 1 4h7m
NAME DESIRED CURRENT READY AGE
replicaset.apps/php-apache-7495ff8f5b 1 1 1 4h7m
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
horizontalpodautoscaler.autoscaling/php-apache Deployment/php-apache 0 %/50% 1 10 1 76m
Cleanup
Remove the application deployment and service
kubectl delete -f php-apache.yaml
Optionally remove the NodePort service, if created
kubectl delete svc php-apache-np
Remove the metrics server
kubectl delete -f components.yaml
kubectl delete hpa php-apache
References
