add shutdownDrainTimeWindow, drains all connections within time range

services/real-time/app.coffee

@@ -113,8 +113,8 @@ shutdownCleanly = (signal) ->
 forceDrain = ->
 	logger.log {delay_ms:Settings.forceDrainMsDelay}, "starting force drain after timeout"
 	setTimeout ()-> 
-		logger.log "starting drain"
-		DrainManager.startDrain(io, 4)
+		logger.log "starting drain over #{Settings.shutdownDrainTimeWindow} mins"
+		DrainManager.startDrainTimeWindow(io, Settings.shutdownDrainTimeWindow)
 	, Settings.forceDrainMsDelay
 
 shutDownInProgress = false

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

@@ -1,6 +1,11 @@
 logger = require "logger-sharelatex"
 
-module.exports =
+module.exports = DrainManager =
+
+	startDrainTimeWindow: (io, minsToDrain)->
+		drainPerMin = io.sockets.clients().length / minsToDrain
+		DrainManager.startDrain(io, drainPerMin / 60)
+
 	startDrain: (io, rate) ->
 		# Clear out any old interval
 		clearInterval @interval

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

@@ -50,6 +50,8 @@ settings =
 
 	forceDrainMsDelay: process.env['FORCE_DRAIN_MS_DELAY'] or false
 
+	shutdownDrainTimeWindow: process.env['SHUTDOWN_DRAIN_TIME_WINDOW'] or 9
+
 	continualPubsubTraffic: process.env['CONTINUAL_PUBSUB_TRAFFIC'] or false
 
 	checkEventOrder: process.env['CHECK_EVENT_ORDER'] or false

services/real-time/test/unit/coffee/DrainManagerTests.coffee

@@ -12,6 +12,24 @@ describe "DrainManager", ->
 			sockets:
 				clients: sinon.stub()
 
+	describe "startDrainTimeWindow", ->
+		beforeEach ->
+			@clients = []
+			for i in [0..1619]
+				@clients[i] = {
+					id: i
+					emit: sinon.stub()
+				}
+			@io.sockets.clients.returns @clients
+			@DrainManager.startDrain = sinon.stub()
+
+		it "should set a drain rate fast enough", (done)->
+			@DrainManager.startDrainTimeWindow(@io, 9)
+			console.log(@DrainManager.startDrain.args[0])
+			@DrainManager.startDrain.calledWith(@io, 3).should.equal true
+			done()
+
+
 	describe "reconnectNClients", ->
 		beforeEach ->
 			@clients = []