[SpaceAlarm]

function server1 (){

var  hostParamsArray =  new Array();
     hostParamsArray[0] =  { host: '', port: 22, username: '', password: '' };
	 hostParamsArray[1] =  { host: '', port: 22, username: '', password: '' };
	  
var command = "", conn = [];	
for (var i = 0; i < hostParamsArray.length; i++) {
    conn[i] = new Client();
    conn[i].on('ready', function() {
    logger.info('SSH Successful connection:  Server#' +(i + 1))
	command = "touch test.log";
    conn[i].exec(command,function(err, stream) {
    if (err) throw err;
    stream.on('close', function() {
      console.log('Stream :: close');
      conn[i].end();
    }).on('data', function(data) {
      console.log('STDOUT: ' + data);
	  if(data.indexOf('123') + 1){
		logger.info('Update');
	  }
    }).stderr.on('data', function(data) {
      console.log('STDERR: ' + data);
    });
  });
}).connect(hostParamsArray[i])
        conn[i].on('error', function(err) {
            console.log(err);
});
}}

Значения в параметрах подключения естественно подставлены)

conn[i].exec(command,function(err, stream) {
           ^
TypeError: Cannot read property 'exec' of undefined