{AKS} az aks create: Raise a ClientRequestError when creating the same cluster again

src/aks-preview/azext_aks_preview/custom.py

@@ -97,6 +97,7 @@
 from azure.cli.core.api import get_config_dir
 from azure.cli.core.azclierror import (
     ArgumentUsageError,
+    ClientRequestError,
     InvalidArgumentValueError,
     MutuallyExclusiveArgumentError,
 )
@@ -720,10 +721,23 @@ def aks_create(
     # DO NOT MOVE: get all the original parameters and save them as a dictionary
     raw_parameters = locals()
 
-    from azure.cli.command_modules.acs._consts import DecoratorEarlyExitException
-    from azext_aks_preview.managed_cluster_decorator import AKSPreviewManagedClusterCreateDecorator
+    # validation for existing cluster
+    existing_mc = None
+    try:
+        existing_mc = client.get(resource_group_name, name)
+    # pylint: disable=broad-except
+    except Exception as ex:
+        logger.debug("failed to get cluster, error: %s", ex)
+    if existing_mc:
+        raise ClientRequestError(
+            f"The cluster '{name}' under resource group '{resource_group_name}' already exists. "
+            "Please use command 'az aks update' to update the existing cluster, "
+            "or select a different cluster name to create a new cluster."
+        )
 
     # decorator pattern
+    from azure.cli.command_modules.acs._consts import DecoratorEarlyExitException
+    from azext_aks_preview.managed_cluster_decorator import AKSPreviewManagedClusterCreateDecorator
     aks_create_decorator = AKSPreviewManagedClusterCreateDecorator(
         cmd=cmd,
         client=client,