How to load asynchronous database url and initiate database connection before express.js app starts?

Question

I have configured the express.js app to run on AWS lambda. The database URL is stored and encrypted in the Amazon KMS service so if I want to use the URL then I have to decrypt the key using AWS KMS service.

// imports
import mongoose from 'mongoose';
import serverless from 'serverless-http';

// KMS promise
const getKmsKey = (key) => { 
  // implementation
  return new Promoise((resolve, reject) => { /* KMS logic */ });
};

// initiate database connection
(async function(){
    mongoose.connect(await getKmsKey('MONGOURL'));
    mongoose.Promise = global.Promise;
})();

const app = express();

// EDIT: added missing app.get example
app.get('/status', async (req, res, next) => {
  // I would like to make sure that mongoose is always initiated here
  res.sendStatus(200);
});

module.exports.handler = serverless(app.default);

Which is the best strategy to make sure that database connection is established before any express route? I see that there exists sync library (https://www.npmjs.com/package/sync) but I think that it's too much overhead just for setting up the database connection and I don't want to use it anywhere else.

Edit: app.get('/status', async (req, res, next) => { was missing in the original post.

sansSpoon · Accepted Answer · 2018-03-07 09:21:12Z

4

I was searching for the same thing and found this great post that explains how you can leverage events to ensure the DB is connected before starting app.listen().

app.on('ready', function() { 
    app.listen(3000, function(){ 
        console.log("app is ready"); 
    }); 
});

mongoose.connect( "mongodb://localhost/mydb" );
mongoose.connection.once('open', function() { 
    // All OK - fire (emit) a ready event. 
    app.emit('ready'); 
});

You could put all your routes in a seperate module and:

app.on('ready', function() { 
    app.use('/', require('./routes'));
    app.listen(3000, function(){ 
        console.log("app is ready"); 
    }); 
});

answered Mar 7, 2018 at 9:21

sansSpoon

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wscourge · Accepted Answer · 2018-01-23 08:34:36Z

1

Just await mongoose.connect(await getKmsKey('MONGOURL'));.

answered Jan 23, 2018 at 8:34

wscourge

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Ashish Surana · Accepted Answer · 2018-01-23 08:39:30Z

1

You can use promise also

mongoose.connect(uri, options).then(
  () => { 
    /** ready to use. The `mongoose.connect()` promise resolves to undefined. */
    },
  err => {
    /** handle initial connection error */
    }
);

See http://mongoosejs.com/docs/promises.html for reference

answered Jan 23, 2018 at 8:39

Ashish Surana

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