How to make virtual network deployment idempotent?

[avivansh]

I tried using both API-Version @2023-11-01 & @2023-09-01. But I am still getting the below error when I try to re-deploy my bicep templates.

Error: -

"details":[{"code":"InUseSubnetCannotBeUpdated","message":"Subnet snet-cosno is in use and cannot be updated."

Context: -
I have my virtual network defined and I am creating 2 subnets snet-cosno & snet-kv. Azure cosmos DB is already provisioned and is in the snet-cosno subnet of the vnet. Now when I re-run the deployment, it results in the above error. I am not sure why it's updating snet-cosno subnet when there has been no changes made to my bicep templates. I was assumed the operation would be idempotent and it won't result into any errors.

Code:-

targetScope = 'resourceGroup'

param name string

param region string

param addressPrefix string

param subnets array

param tags object

param ddosProtectionPlanId string

var subnets = [
  {
    name: 'snet-cosno'
    properties: {
      addressPrefix: '<REDACTED>'
      privateLinkServiceNetworkPolicies: 'Enabled'
      privateEndpointNetworkPolicies: 'Disabled'
      networkSecurityGroup: {
        id: resourceId('<REDACTED>')
      }
    }
  }
  {
    name: 'snet-kv'
    properties: {
      addressPrefix: '<REDACTED>'
      privateLinkServiceNetworkPolicies: 'Enabled'
      privateEndpointNetworkPolicies: 'Disabled'
      networkSecurityGroup: {
        id: resourceId('<REDACTED>')
      }
  }
]

resource virtualNetwork 'Microsoft.Network/virtualNetworks@2023-11-01' = {
  name: name
  location: region
  properties: {
    addressSpace: {
      addressPrefixes: [addressPrefix]
    }
    enableDdosProtection: true
    ddosProtectionPlan: {
      id: ddosProtectionPlanId
    }
    subnets: subnets
  }
  tags: tags
}

output name string = virtualNetwork.name

Region I am trying to do deployment is eastus.

Any help, why re-deployment isn't idempotent here? why snet-cosno is getting updated even when there isn't any change?

[avivansh]

@alex-frankel fyi, based on this discussion Azure/azure-quickstart-templates#2786 (comment)