From 0f93571ca5060d6863cb564e916d69beb7370040 Mon Sep 17 00:00:00 2001
From: Min RK <benjaminrk@gmail.com>
Date: Thu, 26 Sep 2019 14:58:26 +0200
Subject: [PATCH] verify proxy is accessible before listening on the hub

lighter weight than check_routes
---
 jupyterhub/app.py | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/jupyterhub/app.py b/jupyterhub/app.py
index 9634773b..54422dd0 100644
--- a/jupyterhub/app.py
+++ b/jupyterhub/app.py
@@ -2452,6 +2452,20 @@ class JupyterHub(Application):
             loop.stop()
             return
 
+        # start the proxy
+        if self.proxy.should_start:
+            try:
+                await self.proxy.start()
+            except Exception as e:
+                self.log.critical("Failed to start proxy", exc_info=True)
+                self.exit(1)
+        else:
+            self.log.info("Not starting proxy")
+
+        # verify that we can talk to the proxy before listening.
+        # avoids delayed failure if we can't talk to the proxy
+        await self.proxy.get_all_routes()
+
         ssl_context = make_ssl_context(
             self.internal_ssl_key,
             self.internal_ssl_cert,
@@ -2489,16 +2503,6 @@ class JupyterHub(Application):
             self.log.error("Failed to bind hub to %s", self.hub.bind_url)
             raise
 
-        # start the proxy
-        if self.proxy.should_start:
-            try:
-                await self.proxy.start()
-            except Exception as e:
-                self.log.critical("Failed to start proxy", exc_info=True)
-                self.exit(1)
-        else:
-            self.log.info("Not starting proxy")
-
         # start the service(s)
         for service_name, service in self._service_map.items():
             msg = (