// sequelize config

var sequelize = new sequelize('database', 'user', 'pass', {
  host: '127.0.0.1',
  dialect: 'mysql',
  port: 3306,
  pool: {
    max: 10,
    min: 0,
    idle: 20000
  }
});

// tunnel config

var config = {
  user:'user',
  host:'sshhost',
  port:22,
  dsthost:'127.0.0.1',
  dstport:3306,
  srchost:'127.0.0.1',
  srcport:3306,
  localhost:'127.0.0.1',
  localport: 3306,
  privatekey: require('fs').readfilesync('/path/to/key')
};

var tunnel = require('tunnel-ssh');
// initiate tunnel

tunnel(config, function (error, server) {
  //....
  if(error) {
    console.error(error);
  } else {
    console.log('server:', server);
    // test sequelize connection
    sequelize.authenticate().then(function(err) {
      console.log('connection established');
    }).catch(function(err) {
      console.error('unable establish connection', err);
    })
  }
})