Overcome default Amazon imposed 16KB userdata limit

[fartbagxp]

• Some Amazon images will only allow up to 16KB, so only 16,000 characters allowed.
  This means that more than putting too many ssh keys (50?, 100?) in there could cause this to blow up.
  One way to get around it would be to use userdata to add a particular user, and continue on to add subsequent keys elsewhere with that user, only removing it at the end.

[robalexdev]

A common way to avoid this is to use a bootstrap script that downloads the a larger script from S3. It complicates the deployment process, as you need to upload to S3 and you should cleanup old scripts, but works fairly well. Uploading/downloading a zip/tarball of scripts also works well when things get more complex.