Fix AttributeError in negotiate_versionstein-eolstein-em2.7.3stable/stein

Seen in kolla-ansible CI, if ironic inspector starts up before ironic
API is properly up, we see the following error:

The PXE filter DnsmasqFilter, state=initialized encountered an
exception: StrictVersion instance has no attribute 'version'; resetting
the filter: AttributeError: StrictVersion instance has no attribute
'version'

Example: http://paste.openstack.org/show/756342/

The usual cause of this error is when StrictVersion is initialised with
a version of None. This suggests to me that max_ver is None.

This leads to an exception being raised that circumvents the client's
retry mechanisms.

In the particular case of kolla-ansible CI, Ironic API is behind a load
balancer, and all backends are down resulting in a 503. The lack of a
retry caused ironic inspector to fail on startup.

This patch catches the case where we get a 4xx or 5xx return code when
checking the version, and raises an error that works with the client's
retry mechanisms.

Change-Id: Ib62ca3ee4626084e5e9b90e93e4fa97938023457
Story: 2006393
Task: 36266
(cherry picked from commit 0e9bf337f1f6aa41f67df2966dacf9e8e897b7da)

2 files changed, 13 insertions, 1 deletions

diff --git a/ironicclient/common/http.py b/ironicclient/common/http.py
index b78c5a6..9fab68b 100644
--- a/ironicclient/common/http.py
+++ b/ironicclient/common/http.py
@@ -118,7 +118,11 @@ class VersionNegotiationMixin(object):
                                 str(self.os_ironic_api_version).split('.')[0])
             else:
                 base_version = API_VERSION
-            return self._make_simple_request(conn, 'GET', base_version)
+            # Raise exception on client or server error.
+            resp = self._make_simple_request(conn, 'GET', base_version)
+            if not resp.ok:
+                raise exc.from_response(resp, method='GET', url=base_version)
+            return resp
 
         version_overridden = False
 
diff --git a/releasenotes/notes/fix-negotiate-version-503-c3cb8d1d4901541a.yaml b/releasenotes/notes/fix-negotiate-version-503-c3cb8d1d4901541a.yaml
new file mode 100644
index 0000000..0b13e25
--- /dev/null
+++ b/releasenotes/notes/fix-negotiate-version-503-c3cb8d1d4901541a.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixes an issue where some failure modes of communication with the Ironic
+    API could result in an exception that circumvents the client's retry
+    mechanisms. In particular this includes HTTP 503 service unavailable which
+    is seen when Ironic operates behind a load balancer, and no backend is
+    available to handle the request.