Does App service instances spread across zones in a region if instance count = No. of zones without enabling zone redundancy ?

Question

We have deployed our API in App Service, and the instance count is set to 3, which matches the number of availability zones in that region.

However, we did not enable zone redundancy when the App Service plan was created. We understand that it's not possible to enable zone redundancy after the plan has been created, as mentioned in the documentation (https://learn.microsoft.com/en-us/azure/reliability/reliability-app-service?pivots=premium#configure-availability-zone-support).

We do not want to delete and recreate the App Service plan, as this would require significant work due to dependencies on other resources.

Our hope is that, with 3 instances (or potentially more), the App Service will automatically distribute the instances across the available zones.

Please share if our understanding is correct.

TIA

Answer 1

Hi,

You need to re-create the app service plan with zone redundancy enabled:

"When you deploy Azure App Service, you can create multiple instances of an App Service plan, which represents the compute workers that run your application code. Although the platform makes an effort to deploy the instances across different fault domains, it doesn't automatically spread the instances across availability zones."

Source

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