Properly implement ec2.get_all_instances filtering by instance id

moto/ec2/models.py

@@ -1,3 +1,4 @@
+import copy
 from collections import defaultdict
 
 from boto.ec2.instance import Instance as BotoInstance, Reservation
@@ -117,6 +118,22 @@ class InstanceBackend(object):
                 instances.append(instance)
         return instances
 
+    def get_reservations_by_instance_ids(self, instance_ids):
+        """ Go through all of the reservations and filter to only return those
+        associated with the given instance_ids.
+        """
+        reservations = []
+        for reservation in self.reservations.values():
+            reservation_instance_ids = [instance.id for instance in reservation.instances]
+            matching_reservation = any(instance_id in reservation_instance_ids for instance_id in instance_ids)
+            if matching_reservation:
+                # We need to make a copy of the reservation because we have to modify the
+                # instances to limit to those requested
+                reservation_copy = copy.deepcopy(reservation)
+                reservation_copy.instances = [instance for instance in reservation_copy.instances if instance.id in instance_ids]
+                reservations.append(reservation_copy)
+        return reservations
+
     def all_reservations(self):
         return self.reservations.values()
 

moto/ec2/responses/instances.py

@@ -7,8 +7,13 @@ from moto.ec2.utils import instance_ids_from_querystring
 
 class InstanceResponse(object):
     def describe_instances(self):
+        instance_ids = instance_ids_from_querystring(self.querystring)
         template = Template(EC2_DESCRIBE_INSTANCES)
-        return template.render(reservations=ec2_backend.all_reservations())
+        if instance_ids:
+            reservations = ec2_backend.get_reservations_by_instance_ids(instance_ids)
+        else:
+            reservations = ec2_backend.all_reservations()
+        return template.render(reservations=reservations)
 
     def run_instances(self):
         min_count = int(self.querystring.get('MinCount', ['1'])[0])

tests/test_ec2/test_instances.py

@@ -50,6 +50,26 @@ def test_instance_launch_and_terminate():
     instance.state.should.equal('shutting-down')
 
 
+@mock_ec2
+def test_get_instances_by_id():
+    conn = boto.connect_ec2()
+    reservation = conn.run_instances('ami-1234abcd', min_count=2)
+    instance1, instance2 = reservation.instances
+
+    reservations = conn.get_all_instances(instance_ids=[instance1.id])
+    reservations.should.have.length_of(1)
+    reservation = reservations[0]
+    reservation.instances.should.have.length_of(1)
+    reservation.instances[0].id.should.equal(instance1.id)
+
+    reservations = conn.get_all_instances(instance_ids=[instance1.id, instance2.id])
+    reservations.should.have.length_of(1)
+    reservation = reservations[0]
+    reservation.instances.should.have.length_of(2)
+    instance_ids = [instance.id for instance in reservation.instances]
+    instance_ids.should.equal([instance1.id, instance2.id])
+
+
 @mock_ec2
 def test_instance_start_and_stop():
     conn = boto.connect_ec2('the_key', 'the_secret')