Fix failover when the last listener is deleted

This patch fixes an issue when deleting the last listener from a load balancer
may trigger a failover.

Story: 2010652
Task: 47683
Change-Id: I02804b7075edac72776b0377b7b283d0c7bfd8a2
(cherry picked from commit ba92aeb946)
(cherry picked from commit e7f4b1b4c2)
(cherry picked from commit 658173e5b7)
(cherry picked from commit 4e15e81208)
(cherry picked from commit c58f2cb591)

octavia/amphorae/backends/health_daemon/health_daemon.py

@@ -156,9 +156,15 @@ def run_sender(cmd_queue):
 
 
 def get_stats(stat_sock_file):
-    stats_query = haproxy_query.HAProxyQuery(stat_sock_file)
-    stats = stats_query.show_stat()
-    pool_status = stats_query.get_pool_status()
+    try:
+        stats_query = haproxy_query.HAProxyQuery(stat_sock_file)
+        stats = stats_query.show_stat()
+        pool_status = stats_query.get_pool_status()
+    except Exception as e:
+        LOG.warning('Unable to query the HAProxy stats (%s) due to: %s',
+                    stat_sock_file, str(e))
+        # Return empty lists so that the heartbeat will still be sent
+        return [], {}
     return stats, pool_status
 
 

octavia/tests/unit/amphorae/backends/health_daemon/test_health_daemon.py

@@ -319,6 +319,14 @@ class TestHealthDaemon(base.TestCase):
         stats_query_mock.show_stat.assert_called_once_with()
         stats_query_mock.get_pool_status.assert_called_once_with()
 
+    @mock.patch('octavia.amphorae.backends.utils.haproxy_query.HAProxyQuery')
+    def test_get_stats_exception(self, mock_query):
+        mock_query.side_effect = Exception('Boom')
+
+        stats, pool_status = health_daemon.get_stats('TEST')
+        self.assertEqual([], stats)
+        self.assertEqual({}, pool_status)
+
     @mock.patch('octavia.amphorae.backends.agent.api_server.'
                 'util.is_lb_running')
     @mock.patch('octavia.amphorae.backends.health_daemon.'

releasenotes/notes/Fix-listener-delete-causing-failover-251efdb79af24c0a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixed an issue when deleting the last listener from a load balancer may
+    trigger a failover.