Fix: Golang aws-sdk fails to parse elbv2:CreateLoadBalancer response (#3639)

The `botocore` response parsers are forgiving when it comes to timestamps,
but a real AWS backend does return time zone details for this attribute.

Verified failure/fix using the Go repo included in the issue report.

Fixes #3516

moto/elbv2/models.py

@@ -7,7 +7,11 @@ from botocore.exceptions import ParamValidationError
 from moto.compat import OrderedDict
 from moto.core.exceptions import RESTError
 from moto.core import BaseBackend, BaseModel, CloudFormationModel
-from moto.core.utils import camelcase_to_underscores, underscores_to_camelcase
+from moto.core.utils import (
+    camelcase_to_underscores,
+    underscores_to_camelcase,
+    iso_8601_datetime_with_milliseconds,
+)
 from moto.ec2.models import ec2_backends
 from moto.acm.models import acm_backends
 from .utils import make_arn_for_target_group
@@ -380,7 +384,7 @@ class FakeLoadBalancer(CloudFormationModel):
         scheme="internet-facing",
     ):
         self.name = name
-        self.created_time = datetime.datetime.now()
+        self.created_time = iso_8601_datetime_with_milliseconds(datetime.datetime.now())
         self.scheme = scheme
         self.security_groups = security_groups
         self.subnets = subnets or []

tests/test_elbv2/test_elbv2.py

@@ -51,6 +51,7 @@ def test_create_load_balancer():
             {"SubnetId": subnet2.id, "ZoneName": "us-east-1b"},
         ]
     )
+    lb.get("CreatedTime").tzinfo.should_not.be.none
 
     # Ensure the tags persisted
     response = conn.describe_tags(ResourceArns=[lb.get("LoadBalancerArn")])