let websocket server be traited config option

IPython/frontend/html/notebook/handlers.py

@@ -168,12 +168,15 b' class AuthenticatedHandler(RequestHandler):'
     @property
     def ws_url(self):
         """websocket url matching the current request
-        
+
         turns http[s]://host[:port] into
                 ws[s]://host[:port]
         """
         proto = self.request.protocol.replace('http', 'ws')
-        return "%s://%s" % (proto, self.request.host)
+        host = self.application.ipython_app.websocket_host # default to config value
+        if host == '':
+            host = self.request.host # get from request
+        return "%s://%s" % (proto, host)
 
 
 class AuthenticatedFileHandler(AuthenticatedHandler, web.StaticFileHandler):

IPython/frontend/html/notebook/notebookapp.py

@@ -295,11 +295,14 b' class NotebookApp(BaseIPythonApplication):'
         """set mathjax url to empty if mathjax is disabled"""
         if not new:
             self.mathjax_url = u''
-    
+
     base_project_url = Unicode('/', config=True,
                                help='''The base URL for the notebook server''')
     base_kernel_url = Unicode('/', config=True,
                                help='''The base URL for the kernel server''')
+    websocket_host = Unicode("", config=True,
+        help="""The hostname for the websocket server."""
+    )
 
     mathjax_url = Unicode("", config=True,
         help="""The url for MathJax.js."""