Autoscaling

Module

The Horizontal Pod Autoscaler automatically scales the number of pods in a replication controller, deployment or replica set based on observed CPU utilization.

Overview

At the end of this module, you will :
  • Learn the format of a YAML Autoscale file
  • Learn how to manage a Autoscale
  • Learn the composition of a Autoscale

Prerequisites

Create the directory data/autoscaling in your home folder to manage the YAML file needed in this module.
mkdir ~/data/autoscaling
This module needs the metrics-server to be deployed on the cluster to get the monitoring values like CPU and memory. Ensure that the module is up and running before continuing.

Create

Looks up a Deployment, ReplicaSet, or ReplicationController by name and creates an autoscaler that uses the given resource as a reference. An autoscaler can automatically increase or decrease number of pods deployed within the system as needed.
Horizontal Pod Autoscaler automatically scales the number of pods in a deployment or replica set based on observed CPU, Memory or Custom Metrics utilization depending the API version used.
The Kubernetes basic autoscaling architecture can be schematized like this :
The create command can directly ask the API resource to create an HorizontalPodAutoscaler in command line or create an HorizontalPodAutoscaler object based on a yaml file definition.

Exercise n°1

  1. 1.
    Run a sample app based on a webserver to expose it on port 80.
  2. 2.
    Create an Horizontal Pod Autoscaler to automatically scale the Deployment if the CPU usage is above 50%.
# Run a sample app in the default namespace
kubectl run php-apache --image=k8s.gcr.io/hpa-example --requests=cpu=200m --limits=cpu=300m --expose --port=80
# Create an Horizontal Pod Autoscaler based on the CPU usage
kubectl autoscale deployment php-apache --cpu-percent=50 --min=3 --max=10

Exercise n°2

  1. 1.
    Run a sample nginx application exposing port 8080
  2. 2.
    Create an Horizontal Pod Autoscaler to automatically scale the Deployment if the memory is above 50%.
kubectl run nginx --image=nginx --requests=memory=500m --limits=memory=1G --expose --port=8080
~/data/autoscaling/01_hpa.yaml
apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
name: nginx
spec:
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: nginx
minReplicas: 1
maxReplicas: 5
metrics:
- type: Resource
resource:
name: memory
target:
type: Utilization
averageUtilization: 80

Get

The get command list the object asked. It could be a single object or a list of multiple objects comma separated. This command is useful to get the status of each object. The output can be formatted to only display some information based on some json search or external tools like tr, sort, uniq.
The default output display some useful information about each services :
  • Name : the name for the newly created object
  • Reference : the object managed by the autoscaler, like Pod name, a Deployment name ...
  • Targets : the metrics defined to autoscale the referenced resource
  • Minpods : the lower limit for the number of pods that can be set by the autoscaler
  • Maxpods : the upper limit for the number of pods that can be set by the autoscaler
  • Replicas : the current replicas number
  • Age : the age of the object from his creation

Exercise n°1

Get the current HorizontalPodAutoscaler resources in the default namespace.
Command
CLI Return
kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
php-apache Deployment/php-apache 0%/50% 3 10 3 16m

Exercise n°2

Stress the Pod created in the previous section and check the HorizontalPoMindAutoscaler associated.
Command
CLI Return
# Connect to the Pod
kubectl run -it load-generator --image=busybox /bin/sh
# Run a loop bash command in the container to stress the CPU
while true; do wget -q -O- http://php-apache.default.svc.cluster.local; done
# Check the Horizontal Pod Autoscaler status
kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
php-apache Deployment/php-apache 76%/50% 3 10 5 17m
Scale the load-generator if you want to stress the php-apache Pods quickly.
Longer Execution Times
The autoscaling can take more than 2 minutes to run. Please be patient. Do not close the window or cancel the operation.

Exercise n°3

Stop to stress the Pod previously created and check that the autoscaler come back to normal.
Command
CLI Return
kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
php-apache Deployment/php-apache 0%/50% 3 10 3 29m

Describe

Once an object is running, it is inevitably a need to debug problems or check the configuration deployed.
The describe command display a lot of configuration information about the Horizontal Pod Autoscaler (labels, annotations, etc.) and the scale policy (selector, type, number of pods, ...).
This command is really useful to introspect and debug an object deployed in a cluster.

Exercise n°1

Describe one of the existing Autoscaler in the default namespace.
Command
CLI Return
kubectl describe horizontalpodautoscaler php-apache
Name: php-apache
Namespace: default
Labels: <none>
Annotations: <none>
CreationTimestamp: Wed, 06 Feb 2019 10:39:55 -0500
Reference: Deployment/php-apache
Metrics: ( current / target )
resource cpu on pods (as a percentage of request): 0% (0) / 50%
Min replicas: 3
Max replicas: 10
Conditions:
Type Status Reason Message
---- ------ ------ -------
AbleToScale True ScaleDownStabilized recent recommendations were higher than current one, applying the highest recent recommendation
ScalingActive True ValidMetricFound the HPA was able to successfully calculate a replica count from cpu resource utilization (percentage of request)
ScalingLimited False DesiredWithinRange the desired count is within the acceptable range
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulRescale 36m horizontal-pod-autoscaler New size: 3; reason: Current number of replicas below Spec.MinReplicas
Normal SuccessfulRescale 31m horizontal-pod-autoscaler New size: 4; reason: cpu resource utilization (percentage of request) above target
Normal SuccessfulRescale 28m horizontal-pod-autoscaler New size: 5; reason: cpu resource utilization (percentage of request) above target)
Normal SuccessfulRescale 2m horizontal-pod-autoscaler New size: 4; reason: All metrics below target

Explain

Kubernetes come with a lot of documentation about his objects and the available options in each one. Those information can be fin easily in command line or in the official Kubernetes documentation.
The explain command allows to directly ask the API resource via the command line tools to display information about each Kubernetes objects and their architecture.

Exercise n°1

Get the documentation of a specific field of a resource.
Command
CLI Return
kubectl explain hpa.spec
KIND: HorizontalPodAutoscaler
VERSION: autoscaling/v1
RESOURCE: spec <Object>
DESCRIPTION:
behaviour of autoscaler. More info:
https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status.
specification of a horizontal pod autoscaler.
FIELDS:
maxReplicas <integer> -required-
upper limit for the number of pods that can be set by the autoscaler;
cannot be smaller than MinReplicas.
minReplicas <integer>
lower limit for the number of pods that can be set by the autoscaler,
default 1.
scaleTargetRef <Object> -required-
reference to scaled resource; horizontal pod autoscaler will learn the
current resource consumption and will set the desired number of pods by
using its Scale subresource.
targetCPUUtilizationPercentage <integer>
target average CPU utilization (represented as a percentage of requested
CPU) over all the pods; if not specified the default autoscaling policy
will be used.
Add the --recursive flag to display all of the fields at once without descriptions.

Delete

The delete command delete resources by filenames, stdin, resources and names, or by resources and label selector.
Be careful on the deletion of an autoscaling object, this can have effects in the availability of the services associated.
Note that the delete command does NOT do resource version checks, so if someone submits an update to a resource right when you submit a delete, their update will be lost along with the rest of the resource.

Exercise n°1

Delete the previous autoscaling group created in command line.
# Delete the HorizontalPodAutoscaler
kubectl delete hpa php-apache
# Delete the Pods
kubectl delete deployment php-apache load-generator
# Delete the Services
kubectl delete service php-apache

Module exercise

The purpose of this section is to manage each steps of the lifecycle of an application to better understand each concepts of the Kubernetes course.
The main objective in this module is to understand how to dynamically and automatically manage the number of Pods needed to handle the workload.
For more information about the application used all along the course, please refer to the Exercise App > Voting App link in the left panel.
Based on the principles explain in this module, try by your own to handle this steps. The development of a yaml file is recommended.
The file developed has to be stored in this directory : ~/data/votingapp/10_autoscaling
Exercise
Solution
  1. 1.
    Manage the HorizontalPodAutoscaler of the worker Pods to :
    1. 1.
      Ensure that the worker has minimum one Pods
    2. 2.
      Ensure that the worker has maximum five Pods
    3. 3.
      Ensure that the Pods is autoscaled when the CPU is above 80%.
Create the HorizontalPodAutoscaler to manage the worker workload.
kubectl autoscale deployment worker -n voting-app --cpu-percent=80 --min=1 --max=5
This can be done with a yaml file definition :
~/data/votingapp/10_autoscaling/hpa.yaml
apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
name: worker
namespace: voting-app
spec:
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: worker
minReplicas: 1
maxReplicas: 5
metrics:
- type: Resource
resource:
name: cpu
target:
type: Utilization
averageUtilization: 80
Create the resource based on the previous yaml file definition.
kubectl create -f ~/data/votingapp/10_autoscaling/hpa.yaml

External documentation

Those documentations can help you to go further in this topic :
Copy link
On this page
Module
Create
Get
Describe
Explain
Delete
Module exercise
External documentation