Autoscaling is one of the key features in Kubernetes cluster. It is a feature in which the cluster is capable of increasing the number of nodes as the demand for service response increases and decrease the number of nodes as the requirement decreases. This feature of auto scaling is currently supported in Google Cloud Engine (GCE) and Google Container Engine (GKE) and will start with AWS pretty soon.
In order to set up scalable infrastructure in GCE, we need to first have an active GCE project with features of Google cloud monitoring, google cloud logging, and stackdriver enabled.
First, we will set up the cluster with few nodes running in it. Once done, we need to set up the following environment variable.
Environment Variable
export NUM_NODES = 2
export KUBE_AUTOSCALER_MIN_NODES = 2
export KUBE_AUTOSCALER_MAX_NODES = 5
export KUBE_ENABLE_CLUSTER_AUTOSCALER = true
Once done, we will start the cluster by running kube-up.sh. This will create a cluster together with cluster auto-scalar add on.
./cluster/kube-up.sh
On creation of the cluster, we can check our cluster using the following kubectl command.
$ kubectl get nodes
NAME STATUS AGE
kubernetes-master Ready,SchedulingDisabled 10m
kubernetes-minion-group-de5q Ready 10m
kubernetes-minion-group-yhdx Ready 8m
Now, we can deploy an application on the cluster and then enable the horizontal pod autoscaler. This can be done using the following command.
$ kubectl autoscale deployment <Application Name> --cpu-percent = 50 --min = 1 --
max = 10
The above command shows that we will maintain at least one and maximum 10 replica of the POD as the load on the application increases.
We can check the status of autoscaler by running the $kubclt get hpa command. We will increase the load on the pods using the following command.
$ kubectl run -i --tty load-generator --image = busybox /bin/sh
$ while true; do wget -q -O- http://php-apache.default.svc.cluster.local; done
We can check the hpa by running $ kubectl get hpa command.
$ kubectl get hpa
NAME REFERENCE TARGET CURRENT
php-apache Deployment/php-apache/scale 50% 310%
MINPODS MAXPODS AGE
1 20 2m
$ kubectl get deployment php-apache
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
php-apache 7 7 7 3 4m
We can check the number of pods running using the following command.
jsz@jsz-desk2:~/k8s-src$ kubectl get pods
php-apache-2046965998-3ewo6 0/1 Pending 0 1m
php-apache-2046965998-8m03k 1/1 Running 0 1m
php-apache-2046965998-ddpgp 1/1 Running 0 5m
php-apache-2046965998-lrik6 1/1 Running 0 1m
php-apache-2046965998-nj465 0/1 Pending 0 1m
php-apache-2046965998-tmwg1 1/1 Running 0 1m
php-apache-2046965998-xkbw1 0/1 Pending 0 1m
And finally, we can get the node status.
$ kubectl get nodes
NAME STATUS AGE
kubernetes-master Ready,SchedulingDisabled 9m
kubernetes-minion-group-6z5i Ready 43s
kubernetes-minion-group-de5q Ready 9m
kubernetes-minion-group-yhdx Ready 9m