server proxy error pages from the Hub

jupyterhub/app.py

@@ -937,6 +937,7 @@ class JupyterHub(Application):
             '--api-ip', self.proxy.api_server.ip,
             '--api-port', str(self.proxy.api_server.port),
             '--default-target', self.hub.server.host,
+            '--error-target', url_path_join(self.hub.server.url, 'error'),
         ]
         if self.subdomain_host:
             cmd.append('--host-routing')

jupyterhub/handlers/base.py

@@ -410,6 +410,7 @@ class BaseHandler(RequestHandler):
         """render custom error pages"""
         exc_info = kwargs.get('exc_info')
         message = ''
+        exception = None
         status_message = responses.get(status_code, 'Unknown HTTP Error')
         if exc_info:
             exception = exc_info[1]

jupyterhub/handlers/pages.py

@@ -3,12 +3,14 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+from http.client import responses
+
+from jinja2 import TemplateNotFound
 from tornado import web, gen
 
 from .. import orm
 from ..utils import admin_only, url_path_join
 from .base import BaseHandler
-from urllib.parse import quote
 
 
 class RootHandler(BaseHandler):
@@ -160,9 +162,43 @@ class AdminHandler(BaseHandler):
         self.finish(html)
 
 
+class ProxyErrorHandler(BaseHandler):
+    """Handler for rendering proxy error pages"""
+    
+    def get(self, status_code_s):
+        status_code = int(status_code_s)
+        status_message = responses.get(status_code, 'Unknown HTTP Error')
+        # build template namespace
+        
+        hub_home = url_path_join(self.hub.server.base_url, 'home')
+        message_html = ''
+        if status_code == 503:
+            message_html = ' '.join([
+                "Your server appears to be down.",
+                "Try restarting it <a href='%s'>from the hub</a>" % hub_home
+            ])
+        ns = dict(
+            status_code=status_code,
+            status_message=status_message,
+            message_html=message_html,
+            logo_url=hub_home,
+        )
+
+        self.set_header('Content-Type', 'text/html')
+        # render the template
+        try:
+            html = self.render_template('%s.html' % status_code, **ns)
+        except TemplateNotFound:
+            self.log.debug("No template for %d", status_code)
+            html = self.render_template('error.html', **ns)
+
+        self.write(html)
+
+
 default_handlers = [
     (r'/', RootHandler),
     (r'/home', HomeHandler),
     (r'/admin', AdminHandler),
     (r'/spawn', SpawnHandler),
+    (r'/error/(\d+)', ProxyErrorHandler),
 ]

share/jupyter/hub/templates/error.html

@@ -17,6 +17,11 @@
     {{message}}
   </p>
   {% endif %}
+  {% if message_html %}
+  <p>
+    {{message_html | safe}}
+  </p>
+  {% endif %}
   {% endblock error_detail %}
 </div>