由于mongo db数据库，在部署节点js应用程序时，我总是收到错误消息

2019-11-04T03:22:05.624636+00:00 app[web.1]: Warning: connect.session() MemoryStore is not
2019-11-04T03:22:05.624662+00:00 app[web.1]: designed for a production environment,as it will leak
2019-11-04T03:22:05.624664+00:00 app[web.1]: memory,and will not scale past a single process.
2019-11-04T03:22:05.688888+00:00 app[web.1]: Server is running on port 21283
2019-11-04T03:22:05.69945+00:00 app[web.1]: Database connection failed.
2019-11-04T03:23:23.912369+00:00 heroku[router]: at=error code=H12 desc="Request timeout" method=GET path="/" host=shielded-shore-84d9b-8cd6-ef6d90a21352 fwd="197.210.28.42" dyno=web.1 connect=1ms service=30000ms status=503 bytes=0 protoc
2019-11-04T03:23:46.937619+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=shielded-shore
 fwd="197.210.28.42" dyno=web.1 connect=1ms service=19ms status=404 bytes=520 protocol=https
2019-11-04T03:29:27.250493+00:00 heroku[router]: at=error code=H12 desc="Request timeout" method=GET path="
49e8-ab56-1fd46e5d2b01 fwd="197.210.28.42" dyno=web.1 connect=0ms service=30000ms status=503 bytes=0 protoc
2019-11-04T03:30:35.685046+00:00 heroku[router]: at=error code=H12 desc="Request timeout" method=GET path="
4b2c-88ec-f54913a30c3f fwd="197.210.28.42" dyno=web.1 connect=1ms service=30000ms status=503 bytes=0 protoc