Robust Direct Connections for pg-promise

This is a helper function to assist in creating a 'robust' direct connection to a Postgresql database when using the excellent pg-promise library. The implementation is strongly inspired by https://github.com/vitaly-t/pg-promise/wiki/Robust-Listeners, with some additional configuration and logging hooks added.

As is strongly stated and re-stated in the pg-promise documentation, you probably don't need a direct connection for the majority of use-cases, and should stick to pg-promises own connection management and retry logic. However, if you're using LISTEN and NOTIFY, then some manual retry management is essential- if a network partition or other outage breaks connectivity between your application and the database, you will miss out LISTEN events that occur, even after the outage is over.

Basic Usage

// your-app.ts
import {robustConnection} from 'pg-promise-robust-connection';

const myDb = pgPromise()({/** your connection options **/});

// Your app code, using connection pooling against myDB

robustConnection({
  // The pg-promise connection to spawn the direct connection from
  db: myDB

  // Connect established for the first time or after being disconnected previously
  onConnect: (connection) => {
    console.log('connected!');
    connection.client.on('notification', messageHandler);
    connection.none('LISTEN somechannel');
  },

  // Connection was lost; will attempt to reconnect, but clean up in the meantime
  onDisconnect: (err, context) => {
    console.log('disconnected');
    context.client.removeListener('notification', messageHandler);
  }
});

// Allow a reference to messageHandler to be kept so that we may clean it up on disconnect
const messageHandler = (message) => {
  console.log('Got a message', message)
}

By default, when a connection is lost, it will be retried every 1 second a maximum of 10 times. If the last attempt fails, the connection will be considered to have 'failed permanently'. In this case, process.exit() will be called. Then, it's up to your higher level process handler to try to restart the service. Better to have your Dashboard reporting a dead app than one that is half-functional.

Advanced Usage

Please refer to the documentation of the Options interface for details about the other options that are available.