mongoose-reconnect

Reconnect mongoose connections

Reliable reconnect to a mongoDB instance using mongoose driver.

Table of Contents

• Description
  • Example
• Motivation
  • First connect
  • Reconnect after failure
• Solution
  • First connect
  • Reconnect after failure
• Contribution and License Agreement
• License

Description

reconnect handles the database connection and the mongoose models for you.

Example

var reconnect = require('./mongoose-reconnect');
// let `reconnect` handle the mongoose connection
var db = reconnect('mongodb://localhost/test', { db: {}, server: {} });
// a schema is needed
var anySchema = new Schema({ any: Schema.Types.Mixed });
// register the model
var model = db.model('any', anySchema, 'annies');

// your custom find
function find (query, callback) {
  if (!model()) {
    // react if the connection has gone
    return callback(new Error('no connection'));
  }
  modell().find(query).exec(callback);
}

find({}, function(err, data){
  // ...
});

Motivation

First connect

To connect the mongoose driver to a mongoDB instance a connection is required. This implies that a mongoDb needs to run before any nodeJs Server. In this case a nodeJS server reboot is necessary This needs to be done from outside, e.g. manually by your admin or automatically by forever, pm2, monit.

Try it:

# start your mongoDB instance or this docker container
$ ./scripts/mongo.sh
# start querying the database
$ node test/database.js --disable
# you'll get
Error
    at Object.<anonymous> (mongoose-reconnect/node_modules/mongoose/...

Reconnect after failure

If your database locks up during operations mongoose only retries to a certain number of retries before giving up, which also means that you need to restart your nodeJS server from outside.

Try it:

# start a proxy which allows to cut the connection
$ node test/tcpproxy.js
# start querying the database
$ node test/database.js --disable

Now kill tcpproxy with CTRL+C and wait 1min time. Then restart tcpproxy again. Do this several times until you only see the same error messages. I.e. the reconnection to the database did not happen, as we do not see the search results.

From my understanding this is an issue with the native mongoDB driver.

Solution

Retry the same steps above without the --disable option.

First connect

1. Start node test/database.js
2. From another terminal start node test/tcpproxy.js

$ node test/database.js
0 '2015-05-02T08:52:31.090Z'
>>>no connection
1 '2015-05-02T08:52:31.201Z'
... // tcproxy connected
17 '2015-05-02T08:53:29.189Z'
17 '2015-05-02T08:53:29.213Z' null []

Reconnect after failure

1. Start node test/database.js
2. From another terminal start node test/tcpproxy.js
3. Stop tcpproxy with CTRL+C
4. Start tcpproxy after some time.

Contribution and License Agreement

If you contribute code to this project, you are implicitly allowing your code to be distributed under the MIT license. You are also implicitly verifying that all code is your original work or correctly attributed with the source of its origin and licence.

License

Copyright (c) 2015- commenthol (MIT License)

See LICENSE for more info.