Trouble connecting to RabbitMQ

for some strange reason, I cannot connect to my Rabbit instance hosted on GCE. I have tested curl -i -u user:xxxx http://xxx.xxx.xx.xxx:15672/api/whoami and it works. As soon as I'm trying to connect from my node app with the follwing uri let amqpURI = 'amqp://user:xxxx@xxx.xxx.xx.xxx:5672'; I get the following error:

{ Error: getaddrinfo ENOTFOUND user user:5672
    at errnoException (dns.js:28:10)
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:76:26)
  code: 'ENOTFOUND',
  errno: 'ENOTFOUND',
  syscall: 'getaddrinfo',
  hostname: 'user',
  host: 'user',
  port: 5672 }
Error while connecting to AMQP:  Error: getaddrinfo ENOTFOUND user user:5672

I'm a little bit stuck. I have opend the firewall to the ports 5672and 15672. The user and password cannot be wrong, since the curlworks. Is there anything I have overlooked? Could someone lead me in the right direction? Thx!

via Tino