Horizontal Pod Autoscaler in Kubernetes

When we talk about scaling we should always question ourselves and get the answer to the questions below.

What to Scale ?
When to Scale ?
How to Scale ?

Autoscaling is one of the key features in the Kubernetes cluster. It is a feature in which the cluster is capable of increasing the number of pods/nodes as the demand for service response increases and decreases the number of pod/nodes as the requirement decreases.

Let’s cover up the three-way of autoscaling can be done in Kubernetes.

• Horizontal Pod Autoscaler — HPA
• Vertical Pod Autoscaler — VPA
• Cluster Autoscaler — CA

Horizontal Pod Autoscaler — HPA

As the name implies, HPA scales the quantity of pod replicas.Most DevOps use CPU and memory because the triggers to scale additional pod replicas or less.

High-level HPA workflow

HPA WorkFlow

Prerequisites

• Kubernetes Cluster (I tested with 1.10.11 via KOPS on AWS)
• Resource limit set in deployment (check the default YAML file attached for reference)
• Metric Server installed

How to Setup Metric Server

Assuming you have the below setup in working mode to carry out the testing, I have used the AWS environment and used t2.micro instances for testing. I have also configured a separate instance group (db-pool) for testing

Let's Play with CPU scaling now!

• Let's deploy the PHP app for testing which will be scaled on the base of CPU metrics

$ kubectl run php-apache --image=k8s.gcr.io/hpa-example --requests=cpu=200m --expose --port=80
service/php-apache created
deployment.apps/php-apache created

Create Horizontal Pod Autoscaler

The following command will create a Horizontal Pod Autoscaler that maintains between 1 and 10 replicas of the Pods controlled by the php-apache deployment.

$ kubectl autoscale deployment php-apache --cpu-percent=50 --min=1 --max=10
horizontalpodautoscaler.autoscaling/php-apache autoscaled

We may check the current status of autoscaler by running:

$ kubectl get hpa
NAME       REFERENCE   TARGET    MINPODS   MAXPODS   REPLICAS   AGE
php-apache Deployment/php-apache/scale 0% / 50%  1  10   1       18s

Let's Add the Load

We will start a container, and send an infinite loop of queries to the PHP-apache service (please run it in a different terminal):

$ kubectl run -i --tty load-generator --image=busybox /bin/sh
Hit enter for command prompt
$ while true; do wget -q -O- http://php-apache.default.svc.cluster.local; done

Within a minute or so, we should see the higher CPU load by executing:

$ kubectl get hpa
NAME         REFERENCE                     TARGET      CURRENT   MINPODS   MAXPODS   REPLICAS   AGE
php-apache   Deployment/php-apache/scale   305% / 50%  305%      1         10        1          3m

Here, CPU consumption has increased to 305% of the request. As a result, the deployment was resized to 7 replicas:

$ kubectl get deployment php-apache
NAME         DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
php-apache   7         7         7            7           19m

Stop the load!

In the terminal where we created the container with busybox image, terminate the load generation by typing + C Wait for a minute or so and let's verify the status again

$ kubectl get hpa
NAME         REFERENCE                     TARGET       MINPODS   MAXPODS   REPLICAS   AGE
php-apache   Deployment/php-apache/scale   0% / 50%     1         10        1          11m
$ kubectl get deployment php-apache
NAME         DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
php-apache   1         1         1            1           27m

Cool! You are done, you can scale your pods according to your workload.

👋 Join us today !!

️Follow us on LinkedIn, Twitter, Facebook, and Instagram

If this post was helpful, please click the clap 👏 button below a few times to show your support! ⬇