Change the default Keep-Alive timeout to 95 seconds (#371)

For consistency with the timeouts used by other languages:
- heroku/heroku-buildpack-php#823
- heroku/ruby-getting-started#190
- heroku/python-getting-started#263

Author: colincasey

index.js

@@ -18,6 +18,14 @@ const server = app.listen(port, () => {
   console.log(`Listening on ${port}`)
 })
 
+// The number of seconds an idle Keep-Alive connection is kept open. This should be greater than the Heroku Router's
+// Keep-Alive idle timeout of 90 seconds:
+// - to ensure that the closing of idle connections is always initiated by the router and not the Node.js server
+// - to prevent a race condition if the router sends a request to the app just as Node.js is closing the connection
+// https://devcenter.heroku.com/articles/http-routing#keepalives
+// https://nodejs.org/api/http.html#serverkeepalivetimeout
+server.keepAliveTimeout = 95 * 1000
+
 process.on('SIGTERM', async () => {
   console.log('SIGTERM signal received: gracefully shutting down')
   if (server) {