Added backoff support for route53 throttling.

Instead of erroring out on 400-Throttling responses from route53,
perform exponential backoff retries on the request.

boto/route53/connection.py

@@ -521,12 +521,18 @@ def _retry_handler(self, response, i, next_sleep):
         if response.status == 400:
             code = response.getheader('Code')
 
-            if code and 'PriorRequestNotComplete' in code:
+            if code:
                 # This is a case where we need to ignore a 400 error, as
                 # Route53 returns this. See
                 # http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/DNSLimitations.html
+                if 'PriorRequestNotComplete' in code:
+                    error = 'PriorRequestNotComplete'
+                elif 'Throttling' in code:
+                    error = 'Throttling'
+                else:
+                    return status
                 msg = "%s, retry attempt %s" % (
-                    'PriorRequestNotComplete',
+                    error,
                     i
                 )
                 next_sleep = min(random.random() * (2 ** i),

tests/unit/route53/test_connection.py

@@ -54,19 +54,30 @@ def default_body(self):
 
     def test_typical_400(self):
         self.set_http_response(status_code=400, header=[
-            ['Code', 'Throttling'],
+            ['Code', 'AccessDenied'],
         ])
 
         with self.assertRaises(DNSServerError) as err:
             self.service_connection.get_all_hosted_zones()
 
         self.assertTrue('It failed.' in str(err.exception))
 
-    @mock.patch('time.sleep')
-    def test_retryable_400(self, sleep_mock):
+    def test_retryable_400_prior_request_not_complete(self):
+        # Test ability to retry on ``PriorRequestNotComplete``.
         self.set_http_response(status_code=400, header=[
             ['Code', 'PriorRequestNotComplete'],
         ])
+        self.do_retry_handler()
+
+    def test_retryable_400_throttling(self):
+        # Test ability to rety on ``Throttling``.
+        self.set_http_response(status_code=400, header=[
+            ['Code', 'Throttling'],
+        ])
+        self.do_retry_handler()
+
+    @mock.patch('time.sleep')
+    def do_retry_handler(self, sleep_mock):
 
         def incr_retry_handler(func):
             def _wrapper(*args, **kwargs):