@Yang: Sounds legit, as internal is not the same as external. Beware of the fact that internal traffic is only free when it's in the same availability zone. In the same region is charged with a small amount (~ $0.01).

With kind regards,

Robin Verlangen
Software engineer

W http://www.robinverlangen.nl
E robin@us2.nl

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2012/9/5 Yang <teddyyyy123@gmail.com>
thanks, but if the communication between cluster nodes all resolve to "internal to internal", amazon will not charge the traffic as external traffic, right?

On Tue, Sep 4, 2012 at 7:08 PM, aaron morton <aaron@thelastpickle.com> wrote:
See http://aws.amazon.com/articles/1145?_encoding=UTF8&jiveRedirect=1#12

The external  dns will resolve to the internal IP when resolved internally.

Using the internal IP means you are not charged for IO and it makes it clear you do not expect this service to be access from outside.

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 5/09/2012, at 7:37 AM, Yang <teddyyyy123@gmail.com> wrote:

> http://www.datastax.com/docs/1.1/initialize/cluster_init
>
>
> says:
>
> " Note  In the - seeds list property, include the internal IP addresses of each seed node."
>
> why do I have to use internal IP?
> on a EC2 node,
> hostname resolution seems to directly give its internal IP:
>
> $ host aws1devbic1.biqa.ctgrd.com
> aws1devbic1.biqa.ctgrd.com is an alias for ec2-50-17-3-229.compute-1.amazonaws.com.
> ec2-50-17-3-229.compute-1.amazonaws.com has address 10.28.166.83
>
> so using the public DNS or internal IP seems to be the same thing, or something I'm missing ?
>
> Thanks
> Yang
>