Zone Redundant App Service Errors and Solutions
Published Jan 23 2023 07:18 AM 1,047 Views

 Current requirements/limitations for enabling zone redundancy:


Zone Redundant App Service errors and solutions for different scenarios:


Scenario 1

Symptom: Web sockets error when accessing an App service web app in an app service plan which has enabled Zone Redundancy.

Error: Failed to start the transport 'WebSockets': Error: There was an error with the transport.

Root Cause: This issue happened when these 3 conditions are met.

  • Zone Redundancy enabled.
  • Web Sockets set to on (in App service Settings -> Configuration -> General Settings)
  • ARR affinity set to off (in App service Settings -> Configuration -> General Settings)

Solution: Enable ARR affinity for the app service


Scenario 2

Symptom:  Failed to scale down a Linux App service plan --e.g. from P1V3 to P1V2, it failed with message ---You cannot change the OS hosting your app at this time. Please recreate your app with the desired OS

Network trace shows--- http 400 bad request error when sending the PUT request to

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

                          App service plan has Zone redundancy enabled with autoscale configured with an Auto Scale out rule, setting the minimum and default instance count to be less than 3.

Solution:  Update minimum worker rule in Auto Scale to 3 or use Manual Scale

Version history
Last update:
‎Jan 26 2023 02:30 AM
Updated by: