Changing property ‘platformFaultDomainCount’ is not allowed

While updating VMSS (Virtual machine scale sets) related config through Terraform Scripts or using AZURE REST API you may face Changing property ‘platformFaultDomainCount’ is not allowed. Once we created VMSS with a Fault domain count value we can’t update that value with a different value using REST API | Terraform script. If you’re trying to update the Fault domain count value you’ll get the below error.

Platform Fault Domain Count Error

To get rid of above issue:

1. To delete the VMSS & re-create with a new Fault domain count value.
2. Get the existing Fault domain count value from VMSS & pass that value.

For Example : Using REST API

1. To Create a New VMSS

New VMSS

2. Go to AZURE PORTAL check whether VMSS created or not. Here Instances count I setup by default as 2. we can setup based on requirement.

WEB VMSS

3. Now we’re Trying to update the Fault domain count value 2 -> 3 you’ll get the error 409-Conflict with “Changing property ‘platformFaultDomainCount’ is not allowed.”,

Error

4. To Overcome this issue

Option 1: Get the platformFaultDomainCount value by passing VMSS name to GET API . Then update remaining VMSS configuration values according ORG standards.

GET VMSS

Now Grab the platformFaultDomainCount value and pass into with updated VMSS config. Here testing purpose I updated Tags section.

Update VMSS

Go to Azure portal verify the Tags updated or not.

TEST Tags

Option 2: Delete the Entire VMSS & Re-create the New VMSS with latest ORG standards.

before going to delete VMSS go to AZURE portal filter with Tags whether WEBVMSS exist or not ?

VMSS filter

DELETE

Go to Azure portal & verify whether VMSS deleted or not

VMSS deleted

REF:

1. https://learn.microsoft.com/en-us/rest/api/compute/virtual-machine-scale-sets
2. https://portal.azure.com/