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EC2: Resource name DNS options for subnets #154

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Merged
viren-nadkarni merged 3 commits into from
Apr 3, 2026
+52 −2
Merged

EC2: Resource name DNS options for subnets #154

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a4aa2b6
Add test
viren-nadkarni Apr 1, 2026
1ada0cb
Add implementation
viren-nadkarni Apr 1, 2026
7b60dc2
Fix types
viren-nadkarni Apr 1, 2026
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11 changes: 10 additions & 1 deletion moto/ec2/models/subnets.py
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,11 @@ def __init__(
self.map_public_ip_on_launch = map_public_ip_on_launch
self.assign_ipv6_address_on_creation = ipv6_native
self.ipv6_cidr_block_associations: dict[str, dict[str, Any]] = {}
self.private_dns_name_options_on_launch = {
"HostnameType": "ip-name",
"EnableResourceNameDnsARecord": False,
"EnableResourceNameDnsAAAARecord": False,
}
if ipv6_cidr_block:
self.attach_ipv6_cidr_block_associations(ipv6_cidr_block)

Expand Down Expand Up @@ -631,11 +636,15 @@ def delete_subnet(self, subnet_id: str) -> Subnet:
raise InvalidSubnetIdError(subnet_id)

def modify_subnet_attribute(
self, subnet_id: str, attr_name: str, attr_value: str
self, subnet_id: str, attr_name: str, attr_value: bool
) -> None:
subnet = self.get_subnet(subnet_id)
if attr_name in ("map_public_ip_on_launch", "assign_ipv6_address_on_creation"):
setattr(subnet, attr_name, attr_value)
elif attr_name == "enable_resource_name_dns_a_record_on_launch":
subnet.private_dns_name_options_on_launch[
"EnableResourceNameDnsARecord"
] = attr_value
Comment on lines 637 to +647
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@baermat baermat Apr 2, 2026

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I am quite surprised that the type change does not require any additional changes, especially in tests/snapshots. Can you give more context here?

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@viren-nadkarni viren-nadkarni Apr 2, 2026

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ModifySubnetAttribute is used to modify a subnet parameter. This change makes it support a new parameter. It's actually being tested in the newly added test_private_dns_name_options, where it's used to change the default value.

AWS validation in Moto doesn't work like LocalStack -- it does not record the actual API response, just marks the test as runnable against AWS.

else:
raise InvalidParameterValueError(attr_name)

Expand Down
6 changes: 5 additions & 1 deletion moto/ec2/responses/subnets.py
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,11 @@ def describe_subnets(self) -> ActionResult:
def modify_subnet_attribute(self) -> ActionResult:
subnet_id = self._get_param("SubnetId")

for attribute in ("MapPublicIpOnLaunch", "AssignIpv6AddressOnCreation"):
for attribute in (
"MapPublicIpOnLaunch",
"AssignIpv6AddressOnCreation",
"EnableResourceNameDnsARecordOnLaunch",
):
if self._get_param(f"{attribute}.Value") is not None:
attr_name = camelcase_to_underscores(attribute)
attr_value = self._get_param(f"{attribute}.Value")
Expand Down
37 changes: 37 additions & 0 deletions tests/test_ec2/test_subnets.py
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Expand Up @@ -1017,6 +1017,43 @@ def test_create_ipv6native_subnet(account_id, ec2_client=None, vpc_id=None):
ec2_client.delete_subnet(SubnetId=subnet["SubnetId"])


@pytest.mark.aws_verified
@ec2_aws_verified(create_vpc=True)
def test_private_dns_name_options(ec2_client=None, vpc_id=None):
subnet = None
try:
subnet = ec2_client.create_subnet(
VpcId=vpc_id,
CidrBlock="10.0.0.0/24",
)["Subnet"]

assert "PrivateDnsNameOptionsOnLaunch" in subnet
assert subnet["PrivateDnsNameOptionsOnLaunch"]["HostnameType"] == "ip-name"
assert (
subnet["PrivateDnsNameOptionsOnLaunch"]["EnableResourceNameDnsARecord"]
is False
)
assert (
subnet["PrivateDnsNameOptionsOnLaunch"]["EnableResourceNameDnsAAAARecord"]
is False
)

ec2_client.modify_subnet_attribute(
SubnetId=subnet["SubnetId"],
EnableResourceNameDnsARecordOnLaunch={"Value": True},
)
subnet = ec2_client.describe_subnets(SubnetIds=[subnet["SubnetId"]])["Subnets"][
0
]
assert (
subnet["PrivateDnsNameOptionsOnLaunch"]["EnableResourceNameDnsARecord"]
is True
)
finally:
if subnet:
ec2_client.delete_subnet(SubnetId=subnet["SubnetId"])


@mock_aws
def test_create_subnet_cidr_reservations() -> None:
ec2 = boto3.client("ec2", region_name="us-west-1")
Expand Down