Exercise 4: Scaling the application
In this exercise, we'll leverage the metrics we've observed in the previous step to automatically scale our UI application in response to load.
Enable Resource Limits
Before we can setup autoscaling for our pods, we first need to set resource limits on the pods running in our cluster. Limits allows you to choose the minimum and maximum CPU and memory usage for a pod.
Switch back to the Application Console view and select your project. Navigate to Applications > Deployments, then choose your deployment. Then, choose Actions > Edit Resource Limits.
Hopefully you have your running script simulating load (if not go here), Grafana showed you that your application was consuming anywhere between ".002" to ".02" cores. This translates to 2-20 "millicores". That seems like a good range for our CPU request, but to be safe, let's bump the higher-end up to 30 millicores. In addition, Grafana showed that the app consumes about 25-35 MB of RAM. Set the following resource limits for your deployment now.
Remember to set the correct unit -- millicores and MB (not MiB)
Hit save. If there's an error saying that the deployment has changed, you may need to go back to your deployment, refersh the page, and try again.
Enable Autoscaler
Now that we have resource limits, let's enable autoscaler. Go back to the deployment, but this time choose Actions > Add Autoscaler.
By default, the autoscaler allows you to scale based on CPU or Memory. The UI allows you to do CPU only (for now). Pods are balanced between the minimum and maximum number of pods that you specify. With the autoscaler, pods are automatically created or deleted to ensure that the average CPU usage of the pods is below the CPU request target as defined. In general, you probably want to start scaling up when you get near 50-90% of the CPU usage of a pod. In our case, let's make it 1% to test the autoscaler since we are generating minimal load.
Click Save.
Test Autoscaler
If you're not running the script from the previous exercise, the pods should stay at 1. Check by going to the overview page.
Start simulating load by hitting the page several times, or running the script. You'll see that it starts to scale up:
That's it! You now have a highly available and automatically scaled front-end Node.js application. OpenShift is automatically scaling your application pods since the CPU usage of the pods greatly exceeded 1% of the resource limit, 30 millicores.
Optional
Find the Autoscaler information in the Deployment.
If you're interested in setting up the CLI, follow the steps here. Then, run the following command in your CLI oc get hpa to get information about your horizontal pod autoscaler. Remember to switch to your project first with oc project <project-name>.
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