Surfaces previously hidden topics that had URL conflicts, moves pages to index.md as often as possible
This commit is contained in:
johndmulhausen
@@ -0,0 +1,147 @@
|
||||
---
|
||||
---
|
||||
|
||||
Horizontal pod autoscaling allows to automatically scale the number of pods
|
||||
in a replication controller, deployment or replica set based on observed CPU utilization.
|
||||
In the future also other metrics will be supported.
|
||||
|
||||
In this document we explain how this feature works by walking you through an example of enabling horizontal pod autoscaling for the php-apache server.
|
||||
|
||||
## Prerequisites
|
||||
|
||||
This example requires a running Kubernetes cluster and kubectl in the version at least 1.2.
|
||||
[Heapster](https://github.com/kubernetes/heapster) monitoring needs to be deployed in the cluster
|
||||
as horizontal pod autoscaler uses it to collect metrics
|
||||
(if you followed [getting started on GCE guide](/docs/getting-started-guides/gce),
|
||||
heapster monitoring will be turned-on by default).
|
||||
|
||||
## Step One: Run & expose php-apache server
|
||||
|
||||
To demonstrate horizontal pod autoscaler we will use a custom docker image based on php-apache server.
|
||||
The image can be found [here](/docs/user-guide/horizontal-pod-autoscaling/image).
|
||||
It defines [index.php](/docs/user-guide/horizontal-pod-autoscaling/image/index.php) page which performs some CPU intensive computations.
|
||||
|
||||
First, we will start a deployment running the image and expose it as a service:
|
||||
|
||||
```shell
|
||||
$ kubectl run php-apache --image=gcr.io/google_containers/hpa-example --requests=cpu=200m --expose --port=80
|
||||
service "php-apache" created
|
||||
deployment "php-apache" created
|
||||
```
|
||||
|
||||
## Step Two: Create horizontal pod autoscaler
|
||||
|
||||
Now that the server is running, we will create the autoscaler using
|
||||
[kubectl autoscale](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/user-guide/kubectl/kubectl_autoscale.md).
|
||||
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 we created in the first step of these instructions.
|
||||
Roughly speaking, the horizontal autoscaler will increase and decrease the number of replicas
|
||||
(via the deployment) to maintain an average CPU utilization across all Pods of 50%
|
||||
(since each pod requests 200 milli-cores by [kubectl run](#kubectl-run), this means average CPU usage of 100 milli-cores).
|
||||
See [here](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/horizontal-pod-autoscaler.md#autoscaling-algorithm) for more details on the algorithm.
|
||||
|
||||
```shell
|
||||
$ kubectl autoscale deployment php-apache --cpu-percent=50 --min=1 --max=10
|
||||
deployment "php-apache" autoscaled
|
||||
```
|
||||
|
||||
We may check the current status of autoscaler by running:
|
||||
|
||||
```shell
|
||||
$ kubectl get hpa
|
||||
NAME REFERENCE TARGET CURRENT MINPODS MAXPODS AGE
|
||||
php-apache Deployment/php-apache/scale 50% 0% 1 10 18s
|
||||
|
||||
```
|
||||
|
||||
Please note that the current CPU consumption is 0% as we are not sending any requests to the server
|
||||
(the ``CURRENT`` column shows the average across all the pods controlled by the corresponding deployment).
|
||||
|
||||
## Step Three: Increase load
|
||||
|
||||
Now, we will see how the autoscaler reacts on the increased load on the server.
|
||||
We will start a container with `busybox` image and an infinite loop of queries to our server inside (please run it in a different terminal):
|
||||
|
||||
```shell
|
||||
$ 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
|
||||
```
|
||||
|
||||
We may examine, how CPU load was increased by executing (it usually takes 1 minute):
|
||||
|
||||
```shell
|
||||
$ kubectl get hpa
|
||||
NAME REFERENCE TARGET CURRENT MINPODS MAXPODS AGE
|
||||
php-apache Deployment/php-apache/scale 50% 305% 1 10 3m
|
||||
|
||||
```
|
||||
|
||||
In the case presented here, it bumped CPU consumption to 305% of the request.
|
||||
As a result, the deployment was resized to 7 replicas:
|
||||
|
||||
```shell
|
||||
$ kubectl get deployment php-apache
|
||||
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
|
||||
php-apache 7 7 7 7 19m
|
||||
```
|
||||
|
||||
**Warning!** Sometimes it may take few steps to stabilize the number of replicas.
|
||||
Since the amount of load is not controlled in any way it may happen that the final number of replicas will
|
||||
differ from this example.
|
||||
|
||||
## Step Four: Stop load
|
||||
|
||||
We will finish our example by stopping the user load.
|
||||
|
||||
In the terminal where we created container with `busybox` image we will terminate
|
||||
infinite ``while`` loop by sending `SIGINT` signal,
|
||||
which can be done using `<Ctrl> + C` combination.
|
||||
|
||||
Then we will verify the result state:
|
||||
|
||||
```shell
|
||||
$ kubectl get hpa
|
||||
NAME REFERENCE TARGET CURRENT MINPODS MAXPODS AGE
|
||||
php-apache Deployment/php-apache/scale 50% 0% 1 10 11m
|
||||
|
||||
$ kubectl get deployment php-apache
|
||||
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
|
||||
php-apache 1 1 1 1 27m
|
||||
```
|
||||
|
||||
As we see, in the presented case CPU utilization dropped to 0, and the number of replicas dropped to 1.
|
||||
|
||||
**Warning!** Sometimes dropping number of replicas may take few steps.
|
||||
|
||||
## Appendix: Other possible scenarios
|
||||
|
||||
### Creating the autoscaler from a .yaml file
|
||||
|
||||
Instead of using `kubectl autoscale` command we can use the [hpa-php-apache.yaml](/docs/user-guide/horizontal-pod-autoscaling/hpa-php-apache.yaml) file, which looks like this:
|
||||
|
||||
```yaml
|
||||
apiVersion: extensions/v1beta1
|
||||
kind: HorizontalPodAutoscaler
|
||||
metadata:
|
||||
name: php-apache
|
||||
namespace: default
|
||||
spec:
|
||||
scaleRef:
|
||||
kind: Deployment
|
||||
name: php-apache
|
||||
subresource: scale
|
||||
minReplicas: 1
|
||||
maxReplicas: 10
|
||||
cpuUtilization:
|
||||
targetPercentage: 50
|
||||
```
|
||||
|
||||
We will create the autoscaler by executing the following command:
|
||||
|
||||
```shell
|
||||
$ kubectl create -f docs/user-guide/horizontal-pod-autoscaling/hpa-php-apache.yaml
|
||||
horizontalpodautoscaler "php-apache" created
|
||||
```
|
||||
Reference in New Issue
Block a user