Fallback coverage backdoor telnet connection to lo

This commit adds a fallback condition for the telnet connection.
If trying to establish a connection to the backdoor fails with
ECONNREFUSED the extension will then try to connect to the same
port on the lo device. Eventlet backdoors currently open on the
lo interface and this is to cover the common (and CI) use case
where the hostname doesn't resolve to 127.0.0.1.

Using the fallback was done to avoid adding a new config option
to specify that the hostname that is in the DB for the service
doesn't resolve to the lo device, and that the extension should
use just use localhost.

Change-Id: I0321db68cbccf0cddf13d91a77dfb744bb456d87

1 files changed, 20 insertions, 3 deletions

diff --git a/nova/api/openstack/compute/contrib/coverage_ext.py b/nova/api/openstack/compute/contrib/coverage_ext.py
index 6eeb363f2..9e7ed1fe3 100644
--- a/nova/api/openstack/compute/contrib/coverage_ext.py
+++ b/nova/api/openstack/compute/contrib/coverage_ext.py
@@ -19,10 +19,12 @@
 
 import os
 import re
+import socket
 import sys
 import telnetlib
 import tempfile
 
+from oslo.config import cfg
 from webob import exc
 
 from nova.api.openstack import extensions
@@ -39,6 +41,7 @@ from nova.scheduler import rpcapi as scheduler_api
 
 LOG = logging.getLogger(__name__)
 authorize = extensions.extension_authorizer('compute', 'coverage_ext')
+CONF = cfg.CONF
 
 
 class CoverageController(object):
@@ -55,6 +58,7 @@ class CoverageController(object):
         self.services = []
         self.combine = False
         self._cover_inst = None
+        self.host = CONF.host
         super(CoverageController, self).__init__()
 
     @property
@@ -71,7 +75,7 @@ class CoverageController(object):
     def _find_services(self, req):
         """Returns a list of services."""
         context = req.environ['nova.context']
-        services = db.service_get_all(context, False)
+        services = db.service_get_all(context)
         hosts = []
         for serv in services:
             hosts.append({"service": serv["topic"], "host": serv["host"]})
@@ -140,8 +144,21 @@ class CoverageController(object):
         ports = self._find_ports(req, hosts)
         self.services = []
         for service in ports:
-            service['telnet'] = telnetlib.Telnet(service['host'],
-                                                 service['port'])
+            try:
+                service['telnet'] = telnetlib.Telnet(service['host'],
+                                                     service['port'])
+            # NOTE(mtreinish): Fallback to try connecting to lo if
+            # ECONNREFUSED is raised. If using the hostname that is returned
+            # for the service from the service_get_all() DB query raises
+            # ECONNREFUSED it most likely means that the hostname in the DB
+            # doesn't resolve to 127.0.0.1. Currently backdoors only open on
+            # loopback so this is for covering the common single host use case
+            except socket.error as e:
+                if 'ECONNREFUSED' in e and service['host'] == self.host:
+                        service['telnet'] = telnetlib.Telnet('127.0.0.1',
+                                                             service['port'])
+                else:
+                    raise e
             self.services.append(service)
             self._start_coverage_telnet(service['telnet'], service['service'])