From a4aa2b6a59928f90af789c9e5f76dadfdcf31651 Mon Sep 17 00:00:00 2001
From: Viren Nadkarni <viren.nadkarni@gmail.com>
Date: Wed, 1 Apr 2026 17:59:30 +0530
Subject: [PATCH 1/3] Add test

---
 tests/test_ec2/test_subnets.py | 37 ++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/tests/test_ec2/test_subnets.py b/tests/test_ec2/test_subnets.py
index 8f971400c5fe..9151f875a39e 100644
--- a/tests/test_ec2/test_subnets.py
+++ b/tests/test_ec2/test_subnets.py
@@ -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")

From 1ada0cbe206a87995f62509efc3958499d3216d9 Mon Sep 17 00:00:00 2001
From: Viren Nadkarni <viren.nadkarni@gmail.com>
Date: Wed, 1 Apr 2026 17:59:52 +0530
Subject: [PATCH 2/3] Add implementation

---
 moto/ec2/models/subnets.py    | 11 ++++++++++-
 moto/ec2/responses/subnets.py |  6 +++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/moto/ec2/models/subnets.py b/moto/ec2/models/subnets.py
index 0197eab4b2dc..0c4ffb7f3fdc 100644
--- a/moto/ec2/models/subnets.py
+++ b/moto/ec2/models/subnets.py
@@ -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)
 
@@ -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: str | 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
         else:
             raise InvalidParameterValueError(attr_name)
 
diff --git a/moto/ec2/responses/subnets.py b/moto/ec2/responses/subnets.py
index 1b9fdd3782a8..27e96ac54487 100644
--- a/moto/ec2/responses/subnets.py
+++ b/moto/ec2/responses/subnets.py
@@ -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")

From 7b60dc2e87b2258f2945565a40c37b16efed60dd Mon Sep 17 00:00:00 2001
From: Viren Nadkarni <viren.nadkarni@gmail.com>
Date: Wed, 1 Apr 2026 18:38:00 +0530
Subject: [PATCH 3/3] Fix types

---
 moto/ec2/models/subnets.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/moto/ec2/models/subnets.py b/moto/ec2/models/subnets.py
index 0c4ffb7f3fdc..272fab44a5d3 100644
--- a/moto/ec2/models/subnets.py
+++ b/moto/ec2/models/subnets.py
@@ -636,7 +636,7 @@ 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 | bool
+        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"):