Kubernetes Horizontal Pod Auto-scaling


With Horizontal Pod Autoscaling, Kubernetes automatically scales the number of pods in a replication controller, deployment or replica set based on observed CPU utilization (or, with alpha support, on some other, application-provided metrics).

The Horizontal Pod Autoscaler is implemented as a Kubernetes API resource and a controller. The resource determines the behavior of the controller. The controller periodically adjusts the number of replicas in a replication controller or deployment to match the observed average CPU utilization to the target specified by user.


  • Metrics Server. This needs to be setup if you are using kubeadm etc. and replaces heapster starting with kubernetes version 1.8.
  • Resource Requests and Limits. Defining CPU as well as Memory requirements for containers in Pod Spec is a must.

Deploying Metrics Server

Kubernetes Horizontal Pod Autoscaler along with kubectl top command depends on the core monitoring data such as cpu and memory utilization which is scraped and provided by kubelet, which comes with in built cadvisor component. Earlier, you would have to install a additional component called heapster in order to collect this data and feed it to the hpa controller. With 1.8 version of Kubernetes, this behavior is changed, and now metrics-server would provide this data. Metric server is being included as a essential component for kubernetes cluster, and being incroporated into kubernetes to be included out of box. It stores the core monitoring information using in-memory data store.

If you try to pull monitoring information using the following commands

kubectl top pod

kubectl top node it does not show it, rather gives you a error message similar to


Error from server (NotFound): the server could not find the requested resource (get services http:heapster:)
Even though the error mentions heapster, its replaced with metrics server by default now.

Deploy metric server with the following commands,

git clone  https://github.com/kubernetes-incubator/metrics-server.git
kubectl apply -f kubectl create -f metrics-server/deploy/1.8+/


kubectl get deploy,pods -n kube-system --selector='k8s-app=metrics-server'

[sample output]

NAME                                   DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
deployment.extensions/metrics-server   1         1         1            1           28m

NAME                                  READY     STATUS    RESTARTS   AGE
pod/metrics-server-6fbfb84cdd-74jww   1/1       Running   0          28m

Monitoring has been setup.

Defining Resource Requests and Limits

file eample: vote-deploy.yaml

- name: app
  image: schoolofdevops/vote:v4
    - containerPort: 80
      protocol: TCP
  - configMapRef:
      name: vote
      cpu: "200m"
      memory: "250Mi"
      cpu: "100m"
      memory: "50Mi"

then apply:

kubectl apply -f vote-deploy.yaml

Create a HPA

file: vote-hpa.yaml

apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
  name: vote
  minReplicas: 4
  maxReplicas: 15
  targetCPUUtilizationPercentage: 40
    apiVersion: apps/v1
    kind: Deployment
    name: vote


kubectl apply -f vote-hpa.yaml


kubectl get hpa

kubectl describe hpa vote

kubectl get pod,deploy

Load Test

file: loadtest-job.yaml

apiVersion: batch/v1
kind: Job
  name: loadtest
      - name: siege
        image: schoolofdevops/loadtest:v1
        command: ["siege",  "--concurrent=5", "--benchmark", "--time=10m", "http://vote"]
      restartPolicy: Never
  backoffLimit: 4

And launch the loadtest:

kubectl apply -f loadtest-job.yaml

To monitor while the load test is running ,

watch kubectl top pods

To get information about the job:

kubectl get jobs
kubectl describe  job loadtest

To check the load test output:

kubectl logs  -f loadtest-xxxx

[replace loadtest-xxxx with the actual pod id.]

[Sample Output]

** SIEGE 3.0.8
** Preparing 15 concurrent users for battle.
avia@kube-01:~# kubectl logs vote-loadtest-tv6r2 -f
** SIEGE 3.0.8
** Preparing 15 concurrent users for battle.


Lifting the server siege...      done.

Transactions:              41618 hits
Availability:              99.98 %
Elapsed time:             299.13 secs
Data transferred:         127.05 MB
Response time:              0.11 secs
Transaction rate:         139.13 trans/sec
Throughput:             0.42 MB/sec
Concurrency:               14.98
Successful transactions:       41618
Failed transactions:               8
Longest transaction:            3.70
Shortest transaction:           0.00

FILE: /var/log/siege.log
You can disable this annoying message by editing
the .siegerc file in your home directory; change
the directive 'show-logfile' to false

Now check the job status again

kubectl get jobs
vote-loadtest   1         1            10m

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