I'm using Elastic Beanstalk for a web app. (Automatic set up of EC2, an RDS db, etc).
I've been using a custom AMI (based on the default Elastic Beanstalk) because of my need for some specific packages too large to install with a config file.
I noticed the other day that my dashboard shows an option to update platform version under configuration. For example, from 64bit Amazon Linux 2015.03 to 64bit Amazon Linux 2015.09.
How will this affect my custom AMI? Will it overwrite it?
What is the best way to update a custom AMI from, for example, 64bit Amazon Linux 2015.03 to 64bit Amazon Linux 2015.09?
If you update the AMI to theirs, it won't contain your custom modifications. You would need to make these modifications yourself to your base AMI.
I've had success using CI (jenkins) to build my AMIs with Packer via puppet. This allows me to set the base AMI to the newer one and end up with an updated AMI automatically. Jenkins then tells beanstalk to use the new AMI it built.