[misc] forcefully disconnect stale clients from shutdown process

services/real-time/app.js

@@ -155,7 +155,20 @@ function drainAndShutdown(signal) {
         { signal },
         `received interrupt, starting drain over ${shutdownDrainTimeWindow} mins`
       )
-      DrainManager.startDrainTimeWindow(io, shutdownDrainTimeWindow)
+      DrainManager.startDrainTimeWindow(io, shutdownDrainTimeWindow, () => {
+        setTimeout(() => {
+          const staleClients = io.sockets.clients()
+          if (staleClients.length !== 0) {
+            logger.warn(
+              { staleClients: staleClients.map((client) => client.id) },
+              'forcefully disconnecting stale clients'
+            )
+            staleClients.forEach((client) => {
+              client.disconnect()
+            })
+          }
+        }, Settings.gracefulReconnectTimeoutMs)
+      })
       shutdownCleanly(signal)
     }, statusCheckInterval)
   }

services/real-time/app/js/DrainManager.js

@@ -1,13 +1,13 @@
 const logger = require('logger-sharelatex')
 
 module.exports = {
-  startDrainTimeWindow(io, minsToDrain) {
+  startDrainTimeWindow(io, minsToDrain, callback) {
     const drainPerMin = io.sockets.clients().length / minsToDrain
     // enforce minimum drain rate
-    this.startDrain(io, Math.max(drainPerMin / 60, 4))
+    this.startDrain(io, Math.max(drainPerMin / 60, 4), callback)
   },
 
-  startDrain(io, rate) {
+  startDrain(io, rate, callback) {
     // Clear out any old interval
     clearInterval(this.interval)
     logger.log({ rate }, 'starting drain')
@@ -24,7 +24,11 @@ module.exports = {
       pollingInterval = 1000
     }
     this.interval = setInterval(() => {
-      this.reconnectNClients(io, rate)
+      const requestedAllClientsToReconnect = this.reconnectNClients(io, rate)
+      if (requestedAllClientsToReconnect && callback) {
+        callback()
+        callback = undefined
+      }
     }, pollingInterval)
   },
 
@@ -48,6 +52,8 @@ module.exports = {
     }
     if (drainedCount < N) {
       logger.log('All clients have been told to reconnectGracefully')
+      return true
     }
+    return false
   }
 }

services/real-time/config/settings.defaults.js

@@ -123,6 +123,16 @@ const settings = {
 
   shutdownDrainTimeWindow: process.env.SHUTDOWN_DRAIN_TIME_WINDOW || 9,
 
+  // The shutdown procedure asks clients to reconnect gracefully.
+  // 3rd-party/buggy clients may not act upon receiving the message and keep
+  //  stale connections alive. We forcefully disconnect them after X ms:
+  gracefulReconnectTimeoutMs:
+    parseInt(process.env.GRACEFUL_RECONNECT_TIMEOUT_MS, 10) ||
+    // The frontend allows actively editing users to keep the connection open
+    //  for up-to ConnectionManager.MAX_RECONNECT_GRACEFULLY_INTERVAL=45s
+    // Permit an extra delay to account for slow/flaky connections.
+    (45 + 30) * 1000,
+
   continualPubsubTraffic: process.env.CONTINUAL_PUBSUB_TRAFFIC || false,
 
   checkEventOrder: process.env.CHECK_EVENT_ORDER || false,