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When creating a new instance on AWS using an official Ubuntu 12.04 server AMI, what differences are there compared to if I was to do a standard server install on a computer of my own?

For example, the default user is 'ubuntu'. An SSH public key is added to that users authorized_keys file. Sudo is passwordless for that user. PasswordAuthentication is disabled for SSH. etc etc.

Configurations have been changed from their defaults, and I'd like to know if there is a list, or somewhere I could find out the modifications made.

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up vote 3 down vote accepted

No official list exists. However, they publish the build scripts they use here:

You can check them out with the following command:

bzr branch lp:~ubuntu-on-ec2/vmbuilder/automated-ec2-builds

Most of the changes occur from packages installed. For example, the meta package used is ubuntu-cloud instead of ubuntu-server. This includes a different kernel, cloud-init, aws tools, and probably other packages. Cloud-init itself does quite a bit such as changes to apt-get, downloading ssh keys, and loading scripts from amazon user-data. I don't know for certain, but I believe it also makes the ubuntu user and changes your sshd_config to disable PasswordAuthentication. You would need to check the cloud-init deb for that.

Bottom line is that you are unlikely to find all the changes. However, you seem to have found the most important ones. It is the changes to login that really matter. Everything else is just the addition of tools and packages not found elsewhere. If you want to truly understand the AMI and how it works with amazon, I highly recommend learning cloud-init. Cloud-init is a powerful tool for doing some very advanced things with AMIs.

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