Express server crashing due to MongoDB connection loss - express

Question

I am having issues with an HTTP Node.js server built with:
Ubuntu 14.04
MongoDB 3.0.4
iojs v2.3.3
express=4.10.*
mongodb=1.4.34
The following middleware are being used:
app.use(response_time());
app.use(body_parser.urlencoded({extended: true}));
app.use(body_parser.json());
var MongoClient = require('mongodb').MongoClient;
app.use(function (req, res, next) {
var connection_options = {auto_reconnect: false};
MongoClient.connect(config.server.db, connection_options, function (err, db) {
if (err) {
log.error(err); // Logging error.
return next(err);
}
req.db = db;
next();
});
});
The server started running at 20:40:10 and successfully handled multiple requests.
At 02:59:02, the following error started to get logged on every request:
02:59:02.114Z ERROR CrowdStudy: failed to connect to [127.0.0.1:27017]
Error: failed to connect to [127.0.0.1:27017]
at null.<anonymous> (/home/ncphillips/Projects/crowdstudy/node_modules/mongodb/lib/mongodb/connection/server.js:555:74)
at emitThree (events.js:97:13)
at emit (events.js:175:7)
at null.<anonymous> (/home/ncphillips/Projects/crowdstudy/node_modules/mongodb/lib/mongodb/connection/connection_pool.js:156:15)
at emitTwo (events.js:87:13)
at emit (events.js:172:7)
at Socket.<anonymous> (/home/ncphillips/Projects/crowdstudy/node_modules/mongodb/lib/mongodb/connection/connection.js:534:10)
at emitOne (events.js:77:13)
at Socket.emit (events.js:169:7)
at emitErrorNT (net.js:1237:8)
My initial suspicion was that I was that the connection pool was filling up because I don't have anything to handle calling req.db.close(). I thought that passing in the options {auto_reconnect: false} would fix this issue by automatically closing the connection after some time, but it seems I was wrong.
Note that restarting the server fixes the issue, so I believe the problem has to do with Node rather than Mongo.
If this has to do with the connection pool, is there some setting I can pass to fix this, or can I have an end-ware that makes sure the connection always gets closed?
Thanks a lot to anyone who can help me out!

Answer 1

autoReconnect is an option that should be passed to the server configuration:
MongoClient.connect(config.server.db, {
server : { autoReconnect : false }
}, ...);
The documentation contains some errors: it states that the default setting is false (which it isn't), and it also states that autoReconnect should be set in an object called socketOptions (which it shouldn't).
You can add various event listeners to the db object that gets passed back, to detect when the connection to the database got closed/reconnected/...:
db.on('close', function(reason) { ... });
db.on('reconnect', function(db) { ... });
More events here.