Enable remote debugging for nova

This patch added 2 command line parameters which are used to
connect to an external debugger such as pycharm or eclipse.
This feature is used when you want to connect to a nova
service via a debugger running on a different host.
To use it you start the nova service with  the following
command line parameters

--remote_debug-host <where the debugger is running>
--remote_debug-port <port> it's listening on>.

DocImpact
Closes-bug: #1251021
Change-Id: I6ede9bf0813eafbeb91d858c297d4c160aafceba

doc/source/devref/development.environment.rst

@@ -142,6 +142,20 @@ basis by running::
 
      $ tools/with_venv.sh <your command>
 
+Using a remote debugger
+----------------------
+
+Some modern IDE such as pycharm (commercial) or Eclipse (open source) support remote debugging.  In order to run nova with remote debugging, start the nova process
+with the following parameters
+--remote_debug-host <host IP where the debugger is running>
+--remote_debug-port <port it is listening on>
+
+Before you start your nova process, start the remote debugger using the instructions for that debugger.
+For pycharm - http://blog.jetbrains.com/pycharm/2010/12/python-remote-debug-with-pycharm/
+For Eclipse - http://pydev.org/manual_adv_remote_debugger.html
+
+More detailed instructions are located here - http://novaremotedebug.blogspot.com
+
 Contributing Your Work
 ----------------------
 

etc/nova/nova.conf.sample

@@ -2439,6 +2439,27 @@
 #topics=notifications
 
 
+[remote_debug]
+
+#
+# Options defined in nova.service
+#
+
+# Debug host (ip or name) to connect. Note that using the
+# remote debug option changes how Nova uses the eventlet
+# library to support async IO. This could result in failures
+# that do not occur under normal operation. Use at your own
+# risk. (string value)
+#host=<None>
+
+# Debug port to connect. Note that using the remote debug
+# option changes how Nova uses the eventlet library to support
+# async IO. This could result in failures that do not occur
+# under normal operation. Use at your own risk. (integer
+# value)
+#port=<None>
+
+
 [conductor]
 
 #

nova/cmd/__init__.py

@@ -31,4 +31,8 @@ os.environ['EVENTLET_NO_GREENDNS'] = 'yes'
 
 import eventlet
 
-eventlet.monkey_patch(os=False)
+if '--remote_debug-host' in sys.argv and '--remote_debug-port' in sys.argv:
+    # turn off thread patching to enable the remote debugger
+    eventlet.monkey_patch(os=False, thread=False)
+else:
+    eventlet.monkey_patch(os=False)

nova/service.py

@@ -105,9 +105,27 @@ service_opts = [
                help='maximum time since last check-in for up service'),
     ]
 
+cli_opts = [
+        cfg.StrOpt('host',
+                    help='Debug host (ip or name) to connect. Note '
+                        'that using the remote debug option changes how '
+                        'Nova uses the eventlet library to support async IO. '
+                        'This could result in failures that do not occur '
+                        'under normal operation. Use at your own risk.'),
+
+        cfg.IntOpt('port',
+                    help='Debug port to connect. Note '
+                        'that using the remote debug option changes how '
+                        'Nova uses the eventlet library to support async IO. '
+                        'This could result in failures that do not occur '
+                        'under normal operation. Use at your own risk.')
+
+    ]
+
 CONF = cfg.CONF
 CONF.register_opts(service_opts)
 CONF.import_opt('host', 'nova.netconf')
+CONF.register_cli_opts(cli_opts, 'remote_debug')
 
 
 class Service(service.Service):
@@ -249,6 +267,21 @@ class Service(service.Service):
             periodic_enable = CONF.periodic_enable
         if periodic_fuzzy_delay is None:
             periodic_fuzzy_delay = CONF.periodic_fuzzy_delay
+        if CONF.remote_debug.host and CONF.remote_debug.port:
+            from pydev import pydevd
+            LOG = logging.getLogger('nova')
+            LOG.debug(_('Listening on %(host)s:%(port)s for debug connection'),
+                {'host': CONF.remote_debug.host,
+                 'port': CONF.remote_debug.port})
+            pydevd.settrace(host=CONF.remote_debug.host,
+                            port=CONF.remote_debug.port,
+                            stdoutToServer=False,
+                            stderrToServer=False)
+            LOG.warn(_('WARNING: Using the remote debug option changes how '
+                'Nova uses the eventlet library to support async IO. This '
+                'could result in failures that do not occur under normal '
+                'operation. Use at your own risk.'))
+
         service_obj = cls(host, binary, topic, manager,
                           report_interval=report_interval,
                           periodic_enable=periodic_enable,