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Last week we had zone redundant app services with 2 instances. This week we are prevented from doing so.

Sam Curry 5 Reputation points
2025-07-28T09:37:59.1633333+00:00

Last week we were running an App Service plan with zone redundancy using 2 instances.

The ability to run 2 instead of 3 minimum was recently introduced, as per:

This week we cannot deploy apps to the app service anymore with an error stating we now need 4 instances.

The desired MinimumElasticInstanceCount '2' for the site '{redacted}' must be greater than 3 to support zone redundancy.

^^^ greater than 3 presumably means 4, though we seem to be able to with 3, but last week it was 2.

We can now only deploy after scaling the app service plan up to 3 instances.

This seems like a regression.

If we try to scale down a zone redundant app service plan from 3 instances to 2, the message is:

 App Service Plans with fewer than 3 workers are not allowed for zone redundancy. Requested number of workers: 2.

What has changed? Do we need to somehow reconfigure the app service plan and we apps, or is this an error in Azure validation?

Azure App Service
Azure App Service
Azure App Service is a service used to create and deploy scalable, mission-critical web apps.
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  1. Jordan Selig 10 Reputation points Microsoft Employee
    2025-08-04T20:51:27.3133333+00:00

    Hi there. I'm from the App Service team. We have not changed the requirement back to 3 instances. 2 instances is supported. This appears to be a bug. I've followed up with Ivette who pinged me internally about this and we will handle this from there.

    1 person found this answer helpful.
  2. Alex Burlachenko 13,330 Reputation points Volunteer Moderator
    2025-07-28T11:13:54.17+00:00

    hi Sam,

    thanks for bringing this up on the q&a, really appreciate u sharing the details )

    microsoft quietly updated the requirements for zone redundancy in app service plans. last week 2 instances worked, but now they enforce a minimum of 3. yes, it's a bit of a sudden shift, and the error message could be clearer about the exact number ))

    solution for microsoft app service first, u gotta scale up to at least 3 instances https://learn.microsoft.com/en-au/azure/reliability/reliability-app-service. no way around it, sadly. if u try to deploy with fewer, azure will block u.

    to fix this, go to the app service plan, scale out to 3+ instances, and redeploy. it should work then. if u still hit issues, check the activity log in azure portal sometimes there's a delay or caching weirdness.

    when working with zone redundancy, always check the latest docs before scaling. cloud providers tweak requirements, and what worked yesterday might not today. worth looking into setting up alerts for service updates, so u don't get caught off guard ))

    if u haven't already, review the app service sla https://azure.microsoft.com/support/legal/sla/app-service. just to be sure u're covered.

    if u were testing cost savings with 2 instances, maybe look into reserved instances or spot pricing to offset the extra vm cost. not ideal, but hey, cloud budgets love surprises %)

    let me know if u run into more snags! happy to dig deeper )))

    Best regards,

    Alex

    and "yes" if you would follow me at Q&A - personaly thx.
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