Have you ever attempted to deploy or scale out an App Service Plan and received a 429 response that “Not enough available reserved instance servers to satisfy this request. Currently n instances are available. If you are changing instance size you can reserve up to n instances at this moment. If you are increasing instance count then you can add extra n instances at this moment. Please get available machines and retry later.”?
If so, then we have a new capability within App Service which is going to help to address this and give customers a consistent experience. I’m excited to introduce the preview of the ability to create and scale App Service Plans asynchronously, meaning you can request the eventual number of instances you wish for your plan to scale out to and the platform will take care of ensuring that those instances are made available to your plan without you have to modify and reissue your requests to get to your goal.
Scenario:
You are creating a new App Service Plan and you know you would like that plan to have 15 instances.
Current default behavior:
With the current default behavior you may see your request fail and be told only 6 are available. Then you would have to modify your request to ask for 6 instances, then scale out repeatedly, with small increments whilst the platform makes more instances available, until you reach the target 15 instances.
New Preview Functionality:
With the new functionality you can create your new App Service Plan and request 15 instances and the platform will take care of retrying to provision the full 15 on your behalf. Initially your plan may be created with just six instances but then platform will seek to add the others on your behalf.
Create App Service Plan example:
Let’s take a look at how this behaves in CLI
az group create -n <resourceGroupName> -l <location>
az appservice plan create -g <resourceGroupName> -n <appServicePlanName> --number-of-workers <number of instances you need> --sku <App Service Plan Sku, for example P1v3> --async-scaling-enabled true --location <location>
Then you will see the similar output to below:
az appservice plan create -g asyncasp -n asyncasplinuxexample --number-of-workers 25 --sku p1v3 --async-scaling-enabled true --location northeurope --is-linux
Starting to scale App Service plan asyncasplinuxexample...
Status: InProgress — Scaled to 1 workers of pricing tier P1v3.
Status: InProgress — Scaled to 13 workers of pricing tier P1v3.
Status: InProgress — Scaled to 19 workers of pricing tier P1v3.
Status: InProgress — Scaled to 20 workers of pricing tier P1v3.
Successfully scaled to 25 workers in pricing tier P1v3.
Can I use this functionality for scaling out?
Yes, you can use this functionality for scaling App Service Plans too! The CLI command example is as follows:
az appservice plan update -g <resourceGroupName> -n <App Service Plan Name> --async-scaling-enabled true --number-of-workers <number of workers to scale out to>Summary
This new functionality is available today for both Windows and Linux plans, and across all SKUs apart from free and shared. You can take advantage of this capability via ARM/CLI when creating or scaling App Service Plans. Support for configuring Asynchronous Scaling for App Service Plans in the Azure Portal is rolling out globally.
Microsoft