Diagnose: Deployment 409 Conflict: resource exists with different immutable properties

SYMPTOM Deployment 409 Conflict: resource exists with different immutable properties

CAUSE Re-running a template 409s because a property that cannot change after creation differs (SKU family, Cosmos DB capabilities, some network settings), or a soft-deleted resource still holds the name.

CONFIRM IT CONFIRM: az deployment group show --name [d] -g [rg] --query properties.error.details names the conflicting property; what-if shows the template trying to change it. For name-held: the resource appears in soft-deleted listings (e.g. az keyvault list-deleted).

FIX FIX: immutable property: revert the template to the existing value, or recreate the resource deliberately (backup data first). Soft-deleted name: purge it (az keyvault purge) or wait out retention. Never script delete-then-create on stateful resources as conflict resolution.

VERIFY VERIFY: what-if shows no changes, deployment reports Succeeded.

Diagnostic skill indexed by the exact error string. Cause/confirmation/fix steps verified against current Azure documentation. Evidence: https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/overview