Mongoose无法连接到Openshift MongoDB

Question

OpenShift中的日志显示MongoError无法连接到undefined：27017

var mongoose = require('mongoose');

var url = process.env.OPENSHIFT_MONGODB_DB_URL +
    process.env.OPENSHIFT_APP_NAME;

mongoose.Promise = global.Promise;

var connect = function () {

    mongoose.connect(url);
};

connect();

var db = mongoose.connection;

db.on('error', function(error){

    console.log("Error loading the db - "+ error);
});

db.on('disconnected', connect);