EBS - Defer imports until it's necessary (#5265)

moto/ec2/models/elastic_block_store.py

@@ -1,5 +1,4 @@
 from moto.core import get_account_id, CloudFormationModel
-from moto.kms import kms_backends
 from moto.packages.boto.ec2.blockdevicemapping import BlockDeviceType
 from ..exceptions import (
     InvalidAMIAttributeItemValueError,
@@ -404,6 +403,8 @@ class EBSBackend:
         # https://aws.amazon.com/kms/features/#AWS_Service_Integration
         # An AWS managed CMK is created automatically when you first create
         # an encrypted resource using an AWS service integrated with KMS.
+        from moto.kms import kms_backends
+
         kms = kms_backends[self.region_name]
         ebs_alias = "alias/aws/ebs"
         if not kms.alias_exists(ebs_alias):

moto/kms/models.py

@@ -6,13 +6,13 @@ from cryptography.exceptions import InvalidSignature
 from cryptography.hazmat.primitives import hashes
 
 from cryptography.hazmat.primitives.asymmetric import padding
-from moto.apigateway.exceptions import ValidationException
 
 from moto.core import get_account_id, BaseBackend, BaseModel, CloudFormationModel
 from moto.core.utils import get_random_hex, unix_time, BackendDict
 from moto.utilities.tagging_service import TaggingService
 from moto.core.exceptions import JsonRESTError
 
+from .exceptions import ValidationException
 from .utils import (
     RESERVED_ALIASES,
     decrypt,