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What are Availability Zones? 

Availability Zones, or zone redundancy, refers to the deployment of applications across multiple availability zones within an Azure region. Each availability zone consists of one or more data centers with independent power, cooling, and networking. By leveraging zone redundancy, you can protect your applications and data from data center failures, ensuring uninterrupted service. 

Key Updates 

• The minimum instance requirement for enabling Availability Zones has been reduced from three instances to two, while still maintaining a 99.99% SLA. 

• Many existing App Service plans with two or more instances will automatically support Availability Zones without additional setup. 

• The zone redundant setting for App Service plans and App Service Environment v3 is now mutable throughout the life of the resources. 

• Enhanced visibility into Availability Zone information, including physical zone placement and zone counts, is now provided. 

• For App Service Environment v3, the minimum instance fee for enabling Availability Zones has been removed, aligning the pricing model with the multi-tenant App Service offering. 

The minimum instance requirement for enabling Availability Zones has been reduced from three instances to two. You can now enjoy the benefits of Availability Zones with just two instances since we continue to uphold a 99.99% SLA even with the two-instance configuration. Many existing App Service plans with two or more instances will automatically support Availability Zones without necessitating additional setup. Over the past few years, efforts have been made to ensure that the App Service footprint supports Availability Zones wherever possible, and we’ve made significant gains in doing so. Therefore, many existing customers can enable Availability Zones on their current deployments without needing to redeploy. 

Along with supporting 2-instance Availability Zone configuration, we have enabled Availability Zones on the App Service footprint in regions where only two zones may be available. Previously, enabling Availability Zones required a region to have three zones with sufficient capacity. To account for the growing demand, we now support Availability Zone deployments in regions with just two zones. This allows us to provide you with Availability Zone features across more regions. And with that, we are upholding the 99.99% SLA even with the 2-zone configuration.

Additionally, we are pleased to announce that the zone redundant setting (zoneRedundant property) for App Service plans and App Service Environment v3 is now mutable throughout the life of these resources. This enhancement allows customers on Premium V2, Premium V3, or Isolated V2 plans to toggle zone redundancy on or off as required. With this capability, you can reduce costs and scale to a single instance when multiple instances are not necessary. Conversely, you can scale out and enable zone redundancy at any time to meet your requirements. This ability has been requested for a while now and we are excited to finally make it available. For App Service Environment v3 users, this also means that your individual App Service plan zone redundancy status is now independent of other plans in your App Service Environment. This means that you can have a mix of zone redundant and non-zone redundant plans in an App Service Environment, something that was previously not supported.

In addition to these new features, we also have a couple of other exciting things to share. We are now providing enhanced visibility into Availability Zone information, including the physical zone placement of your instances and zone counts. For our App Service Environment v3 customers, we have removed the minimum instance fee for enabling Availability Zones. This means that you now only pay for the Isolated V2 instances you consume. This aligns the pricing model with the multi-tenant App Service offering. 

For more information as well as guidance on how to use these features, see the updated docs starting on May 19th – Reliability in Azure App Service | Microsoft Learn. 

Azure Portal support for these new features will be available by mid-June 2025. In the meantime, see the documentation to use these new features with ARM/Bicep or the Azure CLI.

Also check out BRK200 breakout session at Microsoft Build 2025 live on May 20th or anytime after via the recording where my team and I will be discussing these new features and many more exciting announcements for Azure App Service. If you’re in the Seattle area and attending Microsoft Build 2025 in person, come meet my team and me at our Expert Meetup Booth. 

FAQ 

Q: What are availability zones? 

Availability zones are physically separate locations within an Azure region, each consisting of one or more data centers with independent power, cooling, and networking. Deploying applications across multiple availability zones ensures high availability and business continuity. 

Q: How do I enable Availability Zones for my existing App Service plan or App Service Environment v3?  

There is a new toggle in the Azure portal that will be enabled if your App Service plan or App Service Environment v3 supports Availability Zones. Your deployment must be on the App Service footprint that supports zones in order to have this capability. There is a new property called “MaximumNumberOfZones”, which indicates the number of zones your deployment supports. If this value is greater than one, you are on the footprint that supports zones and can enable Availability Zones as long as you have two or more instances. If this value is equal to one, you need to redeploy. Note that we are continually working to expand the zone footprint across more App Service deployments.  

Q: Is there an additional charge for Availability Zones? 

There is no additional charge, you only pay for the instances you use. The only requirement is that you use two or more instances. 

Q: Can I change the zone redundant property after creating my App Service plan? 

Yes, the zone redundant property is now mutable, meaning you can toggle it on or off at any time. 

Q: How can I verify the zone redundancy status of my App Service Plans? 

We now display the physical zone for each instance, helping you verify zone redundancy status for audits and compliance reviews.

Q: How do I use these new features?

You can use ARM/Bicep or the Azure CLI at this time. Starting in mid-June, Azure Portal support should be available. The documentation currently shows how to use ARM/Bicep and the Azure CLI to enable these features. The documentation as well as this blog post will be updated once Azure Portal support is available.