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07_autoscaling.md

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Autoscaling

Autoscaling can be configured on pods to enable OpenShift to add or remove pods as load varies. In general, the Horizontal Pod Autoscaler sets:

  • Upper limit of pods
  • Lower limit of pods
  • Metric threshold to use for scaling tasks

Currently CPU and memory metrics are supported, with additional arbitrary metrics support intended for the future.

Video Walkthrough Thumbnail

Video walkthrough

Autoscaling Pods

This lab will provide a simple demonstration of autoscaling based on CPU, as this is configurable in the Web Console.

  • First take some time to discover the configurable fields that belong to a HorizontalPodAutoscaler: oc explain HorizontalPodAutoscaler
  • Create an autoscaler to automatically set the number of pods your app uses:

You are configuring a very low CPU request target (10%) so that you can test the autoscaling easily by browsing the web application. A real production CPU target would be closer to 70-80%.

oc -n [-dev] autoscale deployment/rocketchat-[username] --min 1 --max 10 --cpu-percent=10

  • Browse to the application to generate some load and monitor the behavior of the pods

  • Generate some activity such as creating messages, channels, etc.

  • We'll use a tool called ApacheBench to create some load for our application. You can check if you have ab installed by running ab version. If this returns an error, you can install using sudo apt install apache2-utils which includes the ab utility.

  • Use the command below to benchmark your app using 10,000 requests generated by ab (ApacheBench)

    # update the URL below and grab a new integration URL
# Open RocketChat, go to Adminstration > Integrations >  New Integration > Incoming WebHook
#    Set "Enabled" to "true"
#    Set "Post to Channel"  to "#general"
#    Set "Post as"  as "rocket.cat"
#    Click on "Save Changes" at the bottom
#    Copy "Webhook URL" (see "COPY TO CLIPBOARD" button/link)
#    Make sure the domain matches the exposed route (no "localhost:3000")!!!
#    Paste the command below into your terminal, replace the URL at the end with the URL from your clipboard, and run it to begin the load test:
printf '{"text":"Example message","attachments":[{"title":"Rocket.Chat","title_link":"https://rocket.chat","text":"Rocket.Chat, the best open source chat","image_url":"https://rocket.chat/images/mockup.png","color":"#764FA5"}]}' > /tmp/rocketchat-post-msg.json && ab -p /tmp/rocketchat-post-msg.json -n 10000 -c 10 -T "application/json" http://rocketchat-[username]-[namespace].apps.silver.devops.gov.bc.ca/hooks/[integration]/[token]

  • Review the deployment and try to add or remove replicas by editing its .spec.replicas YAML value

    Editing a deployment's YAML to change the replica count

  • Observe how the autoscaler reacts to your new replica count and changes it

    Topology view showing the autoscaler changing the replica count

  • Remove the autoscaler

    oc -n [-dev] delete hpa/rocketchat-[username]

Next page - Persistent Storage