Add filter "availabilityZone" to DescribeSubnets and add availability zone support too

moto/ec2/models.py

@@ -1695,11 +1695,12 @@ class VPCPeeringConnectionBackend(object):
 
 
 class Subnet(TaggedEC2Resource):
-    def __init__(self, ec2_backend, subnet_id, vpc_id, cidr_block):
+    def __init__(self, ec2_backend, subnet_id, vpc_id, cidr_block, availability_zone):
         self.ec2_backend = ec2_backend
         self.id = subnet_id
         self.vpc_id = vpc_id
         self.cidr_block = cidr_block
+        self._availability_zone = availability_zone
 
     @classmethod
     def create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):
@@ -1715,21 +1716,42 @@ class Subnet(TaggedEC2Resource):
 
     @property
     def availability_zone(self):
-        # This could probably be smarter, but there doesn't appear to be a
-        # way to pull AZs for a region in boto
-        return self.ec2_backend.region_name + "a"
+        if self._availability_zone is None:
+            # This could probably be smarter, but there doesn't appear to be a
+            # way to pull AZs for a region in boto
+            return self.ec2_backend.region_name + "a"
+        else:
+            return self._availability_zone
 
     @property
     def physical_resource_id(self):
         return self.id
 
     def get_filter_value(self, filter_name):
+        """
+        API Version 2014-10-01 defines the following filters for DescribeSubnets:
+
+        * availabilityZone
+        * available-ip-address-count
+        * cidrBlock
+        * defaultForAz
+        * state
+        * subnet-id
+        * tag:key=value
+        * tag-key
+        * tag-value
+        * vpc-id
+
+        Taken from: http://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeSubnets.html
+        """
         if filter_name in ['cidr', 'cidrBlock', 'cidr-block']:
             return self.cidr_block
         elif filter_name == 'vpc-id':
             return self.vpc_id
         elif filter_name == 'subnet-id':
             return self.id
+        elif filter_name == 'availabilityZone':
+            return self.availability_zone
 
         filter_value = super(Subnet, self).get_filter_value(filter_name)
 
@@ -1756,9 +1778,9 @@ class SubnetBackend(object):
             raise InvalidSubnetIdError(subnet_id)
         return subnet
 
-    def create_subnet(self, vpc_id, cidr_block):
+    def create_subnet(self, vpc_id, cidr_block, availability_zone=None):
         subnet_id = random_subnet_id()
-        subnet = Subnet(self, subnet_id, vpc_id, cidr_block)
+        subnet = Subnet(self, subnet_id, vpc_id, cidr_block, availability_zone)
         self.get_vpc(vpc_id)  # Validate VPC exists
 
         # AWS associates a new subnet with the default Network ACL