Have spot requests launch instances.

moto/ec2/models.py

@@ -2517,6 +2517,8 @@ class SpotInstanceRequest(BotoSpotRequest, TaggedEC2Resource):
             default_group = self.ec2_backend.get_security_group_from_name("default")
             ls.groups.append(default_group)
 
+        self.instance = self.launch_instance()
+
     def get_filter_value(self, filter_name):
         if filter_name == 'state':
             return self.state
@@ -2529,6 +2531,18 @@ class SpotInstanceRequest(BotoSpotRequest, TaggedEC2Resource):
 
         return filter_value
 
+    def launch_instance(self):
+        reservation = self.ec2_backend.add_instances(
+            image_id=self.launch_specification.image_id, count=1, user_data=self.user_data,
+            instance_type=self.launch_specification.instance_type,
+            subnet_id=self.launch_specification.subnet_id,
+            key_name=self.launch_specification.key_name,
+            security_group_names=[],
+            security_group_ids=self.launch_specification.groups,
+        )
+        instance = reservation.instances[0]
+        return instance
+
 
 @six.add_metaclass(Model)
 class SpotRequestBackend(object):

moto/ec2/responses/spot_fleets.py

@@ -98,9 +98,9 @@ DESCRIBE_SPOT_FLEET_INSTANCES_TEMPLATE = """<DescribeSpotFleetInstancesResponse
     <activeInstanceSet>
         {% for spot_request in spot_requests %}
         <item>
-            <instanceId>{{ spot_request.instance_id }}</instanceId>
+            <instanceId>{{ spot_request.instance.id }}</instanceId>
             <spotInstanceRequestId>{{ spot_request.id }}</spotInstanceRequestId>
-            <instanceType>{{ spot_request.instance_type }}</instanceType>
+            <instanceType>{{ spot_request.instance.instance_type }}</instanceType>
         </item>
         {% endfor %}
     </activeInstanceSet>