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Asked: 2026-05-25T17:36:41+00:00

I am trying to create a simple client/server application using Thrift which is going

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I am trying to create a simple client/server application using Thrift which is going to be run on EC2.

The example I created works awesome for localhost, but when I try to make the RPC call across two different machines on ec2 (both of which have separately allocated elastic IP addresses), it does not work with the following error:

raceback (most recent call last):
  File "SocialQClient.py", line 25, in <module>
    transport.open()
  File "/usr/local/lib/python2.6/dist-packages/thrift/transport/TTransport.py", line 150, in open
    return self.__trans.open()
  File "/usr/local/lib/python2.6/dist-packages/thrift/transport/TSocket.py", line 90, in open
    raise TTransportException(type=TTransportException.NOT_OPEN, message=message)
thrift.transport.TTransport.TTransportException: Could not connect to <MY-ELASTIC-IP>:9090

I have my security group set up for 0.0.0.0/0 for port 9090 on both machines for TCP. I tried UDP also and it did not fix it. What am I doing wrong?

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1 Answer

  1. Editorial Team

    I am hazarding a guess that when one of your ec2 instance (“node1”) attempts the RPC call to the other ec2 instance (“node2”), node2 returns its internal IP address instead.

    Reference – http://alestic.com/2009/06/ec2-elastic-ip-internal

    Quote:

    This last option uses a little-known feature of the Elastic IP Address
    system as implemented by Amazon EC2:

    When an EC2 instance queries the external DNS name of an Elastic
    IP, the EC2 DNS server returns the internal IP address of the instance
    to which the Elastic IP address is currently assigned.

    And here’s some examples which illustrates how dig returns different values, comparing the scenario where you use a machine outside of Amazon to ping an ec2 instance, versus when you use an ec2 instance to ping another ec2 instance:-

    This is the permanent external DNS name for that Elastic IP address no
    matter how many times you change the instance to which it is assigned.
    If you query this DNS name from outside of EC2, it will resolve to the
    external IP address as shown above:

    $ dig +short ec2-75-101-137-243.compute-1.amazonaws.com
75.101.137.243

    However, if you query this DNS name from inside an EC2 instance, it
    will resolve to the internal IP address for the instance to which it
    is currently assigned:

    $ dig +short ec2-75-101-137-243.compute-1.amazonaws.com
10.254.171.132
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