config: configure default websocket ping interval

* Closes cylc#557
* Sends regular pings to websocket clients to ensure that the connection
  is still active and open at the other end.
* This allows for earlier detection of client-side connection closing.

changes.d/586.feat.md

@@ -0,0 +1,7 @@
+The UI Server is now configured to regularly ping active clients to ensure they
+are alive. This helps the server to detect closed connections sooner, it also
+ensures that open connections do not appear idle to proxy servers which are
+sometimes configured to kill websockets after a period of inactivity.
+You can override or modify this behaviour in your jupyter configuration using
+the `websocket_ping_interval` and `websocket_ping_timeout` configurations, see
+the Jupyter Server reference for more information.

cylc/uiserver/jupyter_config.py

@@ -55,6 +55,10 @@
     )
 ]
 
+# configure websocket pings (helps to detect client-closed connections)
+c.ServerApp.websocket_ping_interval = 10
+c.ServerApp.websocket_ping_timeout = 10
+
 # store JupyterHub runtime files in the user config directory
 USER_CONF_ROOT.mkdir(parents=True, exist_ok=True)
 c.JupyterHub.cookie_secret_file = f'{USER_CONF_ROOT / "cookie_secret"}'

setup.cfg

@@ -54,7 +54,7 @@ install_requires =
     graphene
     graphene-tornado==2.6.*
     graphql-ws==0.4.4
-    jupyter_server>=2.7
+    jupyter_server>=2.13.0
     requests
     psutil
     tornado>=6.1.0  # matches jupyter_server value