Change default num_retries for glance to 3

Previously, the default value of num_retries for glance is 0.
It means that the request to glance is sent only one time.
On the other hand, neutron and cinder clients set the default
value to 3.
To align the default value for retry to other components, we
should change the default value to 3.

Closes-Bug: #1888168
Change-Id: Ibbd4bd26408328b9e1a1128b3794721405631193

nova/conf/glance.py

@@ -52,7 +52,7 @@ Possible values:
   (i.e. "http://10.0.1.0:9292" or "https://my.glance.server/image").
 """),
     cfg.IntOpt('num_retries',
-        default=0,
+        default=3,
         min=0,
         help="""
 Enable glance operation retries.

nova/tests/unit/virt/xenapi/image/test_glance.py

@@ -148,7 +148,7 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)
 
     @mock.patch.object(utils, 'get_auto_disk_config_from_instance')
@@ -169,7 +169,7 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)
         mock_disk_config.assert_called_once_with(self.instance)
 
@@ -190,7 +190,7 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)
         mock_disk_config.assert_called_once_with(self.instance)
 
@@ -211,7 +211,7 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)
 
     @mock.patch.object(common_glance, 'generate_identity_headers')
@@ -231,7 +231,7 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)
 
     @mock.patch.object(time, 'sleep')
@@ -330,5 +330,5 @@ class TestGlanceStore(stubs.XenAPITestBaseNoDB):
         mock_sr_path.assert_called_once_with(self.session)
         mock_extra_header.assert_called_once_with(self.context)
         mock_upload.assert_called_once_with(
-            self.session, 0, mock.ANY, mock.ANY, 'fake_image_uuid',
+            self.session, 3, mock.ANY, mock.ANY, 'fake_image_uuid',
             'fake_sr_path', 'fake_extra_header', **params)

nova/tests/unit/virt/xenapi/test_vm_utils.py

@@ -258,7 +258,7 @@ class FetchVhdImageTestCase(VMUtilsTestBase):
         self.mock_call_plugin.assert_called_once_with(
                 'glance.py',
                 'download_vhd2',
-                0,
+                3,
                 mock.ANY,
                 mock.ANY,
                 extra_headers={'X-Auth-Token': 'auth_token',

releasenotes/notes/increase_glance_num_retries-ddfcd7053631882b.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    The default for ``[glance] num_retries`` has changed from ``0`` to ``3``.
+    The option controls how many times to retry a Glance API call in response
+    to a HTTP connection failure. When deploying Glance behind HAproxy it is
+    possible for a response to arrive just after the HAproxy idle time. As a
+    result, an exception will be raised when the connection is closed resulting
+    in a failed request. By increasing the default value, Nova can be more
+    resilient to this scenario were HAproxy is misconfigured by retrying the
+    request.