var db = mongoose.connect('mongodb://localhost:27017/DB');

// In middleware
app.use(function (req, res, next) {

  // action after response
  var afterResponse = function() {
   logger.info({req: req}, "End request");

    // any other clean ups
    mongoose.connection.close(function () {
      console.log('Mongoose connection disconnected');
    });
  }

  // hooks to execute after response
  res.on('finish', afterResponse);
  res.on('close', afterResponse);

  // do more stuff

  next();
}