We have a particularly unique situation so I will try to be as clear as I can be.
We are a SaaS business that currently runs a LAMP stack application on amazon EC2. We have no autoscaling and we plan to move to it in the very near future. Our deployment processes are moving towards agile development but we're not quite there yet. We run subversion as our version control system from which we manage multiple versions of our code at the same time.
We want to move to autoscaling using Amazon's Autoscaling infrastructure with CloudFormation for our web servers only at the moment. We're currently stuck on coming up with a method to perform updates to our code base all at the same time, whenever we want. The key here is that the update needs to be performed at the same time across all servers (we can allow for a small delay between updates of each server <1 min). I know that Amazon cloud formation can perform updates to the stack, but from what I have read the servers will update on their own time within a 15 minute period. This is of course not feasible as we don't want our clients on different versions of a particular code base.
We've thought about using a custom script on a permanent server that will push commands to update the code base on each server (by forking a process to each instance in the autoscaling group) but don't know if that's the best route. We're also trying to avoid having to re-bake the AMI used in the launch config to have new code in it.
Does anyone know a method that works for them for updating the codebase on autoscaling servers that doesn't require building a new AMI for each release?
Thanks very much for your help!