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The tests will be performed on a cluster consisting of 4 nodes (1 master and 3 worker) with the same flavor. The flavor will also be modified in turn, remaining the same between the VMs in the cluster, multiplying the CPU and RAM by a factor of 2: passing from training medium (2 CPUs and 4GB RAM) to large (4 CPUs and 8GB RAM) and finally xlarge (8 CPUs and 16GB RAM). Finally, the clusters used for the tests are set to "factory settings", ie i.e. they will contain only the starting software of a typical k8s cluster just created. Before we continue, let's familiarize ourselves with a couple of tools suitable for our purposes: Metrics Server and Horizontal Pod Autoscaler.

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Metrics Server deployment will likely not be Ready. If, analyzing the Pod logs, you see the error "unable to fully scrape metrics", then edit the deployment by inserting the flag

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Run and expose php-apache server

To demonstrate HPA , we will use a custom docker image based on the php-apache image. Copy the following lines of code into the Dockerfile and index.php files and place them in the same folder. Then run the docker build . command

FROM php:5-apache
COPY index.php /var/www/html/index.php
RUN chmod a+rx index.php

// These lines of code define the index.php file, which performs some CPU intensive computations
<?php
  $x = 0.0001;
  for ($i = 0; $i <= 1000000; $i++) {
    $x += sqrt($x);
  }
  echo "OK!";
?>

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 Apply the following file, to install a simple PHP web application in the Kubernetes cluster. Then, verify the pods were created.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: php-apache
spec:
  selector:
    matchLabels:
      run: php-apache
  replicas: 1
  template:
    metadata:
      labels:
        run: php-apache
    spec:
      containers:
      - name: php-apache
        image: k8s.gcr.io/hpa-example
        ports:
        - containerPort: 80
        resources:	# <--- Pay attention
          limits:
            cpu: 500m
          requests:
            cpu: 200m
---
apiVersion: v1
kind: Service
metadata:
  name: php-apache
  labels:
    run: php-apache
spec:
  ports:
  - port: 80
  selector:
    run: php-apache

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We will finish our example by stopping the user load. In the terminal where we created the container with busybox image, terminate the load generation by typing <Ctrl> + Cstopping the process, simply deleting the deployment/infinite-calls component or, if you want to reuse it for further testing, scale it to zero replicas. Then, we verify the result state. After : after a minute or so, re-run the two get commands used earlier. You should get that CPU utilization dropped to 0, and so HPA autoscaled the number of replicas back down to 1.