EC2: Add default DHCP options set for VPCs (#6901)

getmoto · Oct 11, 2023 · 7e891f7 · 7e891f7
1 parent 0471cd0
commit 7e891f7
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Showing 4 changed files with 40 additions and 4 deletions.
diff --git a/moto/ec2/models/dhcp_options.py b/moto/ec2/models/dhcp_options.py
@@ -69,6 +69,11 @@ def associate_dhcp_options(self, dhcp_options: DHCPOptionsSet, vpc: Any) -> None
         dhcp_options.vpc = vpc
         vpc.dhcp_options = dhcp_options
 
+    def disassociate_dhcp_options(self, vpc: Any) -> None:
+        if vpc.dhcp_options:
+            vpc.dhcp_options.vpc = None
+        vpc.dhcp_options = None
+
     def create_dhcp_options(
         self,
         domain_name_servers: Optional[List[str]] = None,

diff --git a/moto/ec2/responses/dhcp_options.py b/moto/ec2/responses/dhcp_options.py
@@ -6,10 +6,13 @@ def associate_dhcp_options(self) -> str:
         dhcp_opt_id = self._get_param("DhcpOptionsId")
         vpc_id = self._get_param("VpcId")
 
-        dhcp_opt = self.ec2_backend.describe_dhcp_options([dhcp_opt_id])[0]
         vpc = self.ec2_backend.get_vpc(vpc_id)
 
-        self.ec2_backend.associate_dhcp_options(dhcp_opt, vpc)
+        if dhcp_opt_id == "default":
+            self.ec2_backend.disassociate_dhcp_options(vpc)
+        else:
+            dhcp_opt = self.ec2_backend.describe_dhcp_options([dhcp_opt_id])[0]
+            self.ec2_backend.associate_dhcp_options(dhcp_opt, vpc)
 
         template = self.response_template(ASSOCIATE_DHCP_OPTIONS_RESPONSE)
         return template.render()

diff --git a/moto/ec2/responses/vpcs.py b/moto/ec2/responses/vpcs.py
@@ -374,7 +374,7 @@ def modify_managed_prefix_list(self) -> str:
               {% endfor %}
           </ipv6CidrBlockAssociationSet>
         {% endif %}
-      <dhcpOptionsId>{% if vpc.dhcp_options %}{{ vpc.dhcp_options.id }}{% else %}dopt-1a2b3c4d2{% endif %}</dhcpOptionsId>
+      <dhcpOptionsId>{% if vpc.dhcp_options %}{{ vpc.dhcp_options.id }}{% else %}default{% endif %}</dhcpOptionsId>
       <instanceTenancy>{{ vpc.instance_tenancy }}</instanceTenancy>
       <ownerId> {{ vpc.owner_id }}</ownerId>
       <tagSet>
@@ -475,7 +475,7 @@ def modify_managed_prefix_list(self) -> str:
               {% endfor %}
             </ipv6CidrBlockAssociationSet>
         {% endif %}
-        <dhcpOptionsId>{% if vpc.dhcp_options %}{{ vpc.dhcp_options.id }}{% else %}dopt-7a8b9c2d{% endif %}</dhcpOptionsId>
+        <dhcpOptionsId>{% if vpc.dhcp_options %}{{ vpc.dhcp_options.id }}{% else %}default{% endif %}</dhcpOptionsId>
         <instanceTenancy>{{ vpc.instance_tenancy }}</instanceTenancy>
         <isDefault>{{ vpc.is_default }}</isDefault>
         <ownerId> {{ vpc.owner_id }}</ownerId>

diff --git a/tests/test_ec2/test_dhcp_options.py b/tests/test_ec2/test_dhcp_options.py
@@ -66,6 +66,34 @@ def test_dhcp_options_associate_invalid_vpc_id():
     assert ex.value.response["Error"]["Code"] == "InvalidVpcID.NotFound"
 
 
+@mock_ec2
+def test_dhcp_options_disassociation():
+    """Ensure that VPCs can be set to the 'default' DHCP options set for disassociation."""
+    ec2 = boto3.resource("ec2", region_name="us-west-1")
+    client = boto3.client("ec2", region_name="us-west-1")
+    dhcp_options = ec2.create_dhcp_options(
+        DhcpConfigurations=[
+            {"Key": "domain-name", "Values": [SAMPLE_DOMAIN_NAME]},
+            {"Key": "domain-name-servers", "Values": SAMPLE_NAME_SERVERS},
+        ]
+    )
+    vpc = ec2.create_vpc(CidrBlock="10.0.0.0/16")
+
+    # Ensure newly created VPCs without any DHCP options can be disassociated
+    client.associate_dhcp_options(DhcpOptionsId="default", VpcId=vpc.id)
+    vpc.reload()
+    assert vpc.dhcp_options_id == "default"
+
+    client.associate_dhcp_options(DhcpOptionsId=dhcp_options.id, VpcId=vpc.id)
+    vpc.reload()
+    assert vpc.dhcp_options_id == dhcp_options.id
+
+    # Ensure VPCs with already associated DHCP options can be disassociated
+    client.associate_dhcp_options(DhcpOptionsId="default", VpcId=vpc.id)
+    vpc.reload()
+    assert vpc.dhcp_options_id == "default"
+
+
 @mock_ec2
 def test_dhcp_options_delete_with_vpc():
     """Test deletion of dhcp options with vpc"""