ZoneRedundancyNotAllowedInResourceGroup when creating Multi-AZ App Service Plan after Single-AZ Plan

Question

I am encountering the (Code: ZoneRedundancyNotAllowedInResourceGroup) error when trying to configure a multi-AZ App Service Plan. I have observed the following behavior:

In the first scenario, I created a new resource group and initially deployed an App Service Plan with zone redundancy enabled. After that, I was able to create another App Service Plan in the same resource group with zone redundancy disabled without any issues.

In the second scenario, I created another resource group and first deployed an App Service Plan with zone redundancy disabled. However, when I attempted to create a second App Service Plan in the same resource group with zone redundancy enabled, I encountered the error: (Code: ZoneRedundancyNotAllowedInResourceGroup).

I would like to understand the exact reason for this behavior. Specifically, why am I unable to create a zone-redundant App Service Plan when the first App Service Plan in the resource group was created without zone redundancy?

In this case, do I need to create a new resource group to enable multi-AZ support?

Answer 1

Hello @Ankit Thakkar

ZoneRedundancyNotAllowedInResourceGroup occurs because Azure App Service Plans are deployed on underlying scale units, and zone redundancy is only supported if that scale unit supports availability zones; as per Microsoft documentation, if the plan is on a scale unit that doesn’t support zones, you cannot enable or create a zone‑redundant plan there and must deploy to a new one. Since all plans in the same resource group (same region and OS) are placed on the same infrastructure, the first App Service Plan determines whether that resource group supports zone redundancy.

Therefore, if the first plan is created without zone redundancy, the resource group may be tied to a non‑zone‑redundant scale unit, causing subsequent zone‑redundant deployments to fail; to use multi‑AZ, you need to create a new resource group and deploy the first plan with zone redundancy enabled.

Reference:
https://learn.microsoft.com/en-us/azure/app-service/configure-zone-redundancy?tabs=portal

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Answer 2

Hello @Ankit Thakkar

Thank you for reaching out Microsoft Q&A. I understand your scenario.

The ZoneRedundancyNotAllowedInResourceGroup error occurs because Azure App Service Plans are deployed onto specific underlying scale units, and zone redundancy is only available when that scale unit supports Availability Zones. According to Microsoft guidance, if an App Service Plan is placed on infrastructure that does not support zones, you cannot later enable zone redundancy on that plan or create another zone-redundant plan on the same infrastructure.

In practice, App Service Plans created within the same resource group, region, and operating system type are typically allocated to the same underlying infrastructure stamp. Because of this, the first App Service Plan created in that resource group effectively determines whether zone redundancy is supported there.

As a result, if the initial App Service Plan was created without zone redundancy on a non-AZ-capable scale unit, later attempts to deploy a zone-redundant App Service Plan in that same resource group can fail with ZoneRedundancyNotAllowedInResourceGroup.

To deploy a multi-Availability Zone App Service Plan, the recommended approach is to create a new resource group and ensure the first App Service Plan is created with zone redundancy enabled from the beginning.

Kindly let us know if the above helps or you need further assistance on this issue.

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Answer 3

Zone redundancy support for App Service plans is determined by the scale unit that the resource group is mapped to, and that mapping is effectively decided by the first App Service plan created in that resource group.

From the documentation:

• Zone redundancy is a property of the scale unit where the App Service plan is deployed.
• When a new App Service plan is created, it is assigned to a scale unit based on the resource group.
• Some scale units support availability zones (and therefore zone redundancy); others do not.

This leads to the behavior described:

1. First scenario (works):
   • The first plan in the resource group is created with zone redundancy enabled.
   • Because zone redundancy is explicitly selected at creation time, the plan is placed on a scale unit that supports availability zones.
   • Subsequent plans in the same resource group can be created with zone redundancy either enabled or disabled, because they are all on a scale unit that supports zones.
2. Second scenario (fails):
   • The first plan in the resource group is created without zone redundancy.
   • That first plan is placed on a scale unit that does not support availability zones.
   • Zone redundancy is a property of the scale unit, not just the individual plan. Because the scale unit does not support zones, any attempt to create a zone-redundant plan in that same resource group fails with ZoneRedundancyNotAllowedInResourceGroup.

The documentation explicitly states that:

• If a current App Service plan is in a scale unit that doesn't support zone redundancy, zone redundancy cannot be enabled on that plan.
• When a new App Service plan is created with zone redundancy enabled in a different resource group, it is deployed to a different scale unit.
• Apps and plans cannot move between scale units; redeployment is required.

Therefore, in this situation:

• Yes, to create a zone-redundant App Service plan when the first plan in the existing resource group is non–zone-redundant (and thus on a non–zone-redundant scale unit), a new resource group must be created.
• In that new resource group, create a new App Service plan with zone redundancy explicitly enabled at creation time. This ensures placement on a scale unit that supports availability zones. Additional plans in that resource group can then be created with or without zone redundancy as needed.

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References:

• Configure App Service plans for zone redundancy
• Reliability in Azure App Service
• Reliability in Azure App Service Environment
• Move App Service resources to a new resource group or subscription
• Manage an App Service plan in Azure