In EC2, there is a dependency on the host ip as well. If the ip is modified, then the internal hostname is also different. 
If the hostname is not updated in the os there will be a difference in the instance hostname presented by the ec2 host management and the instance hostname on any stop/start, much like the EBS snapshot scenario described previously. 

On Sep 11, 2013 5:44 AM, "Matthew Miller" <mattdm@fedoraproject.org> wrote:
On Tue, Sep 10, 2013 at 11:47:52PM -0400, Sam Kottler wrote:
> Hi! Sorry about two emails in a row :-)

More activity = good. :)


> I think the update_hostname module causes some confusion on EBS-backed
> instances. Users expect the hostname of their instance to remain
> consistent across reboots and the update_hostname module causes it to be
> reset on boot.
> What do you all think about removing it from the cloud-init configuration?

I don't have a strong opinion here, but in general anything which makes our
cloud-init usage less heavyweight is good with me.

--
Matthew Miller  ☁☁☁  Fedora Cloud Architect  ☁☁☁  <mattdm@fedoraproject.org>
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