I am pretty new to AWS so please excuse my ignorance. We are wanting to have a setup whereby we have a SQL DB instance + web server instance. However we would like the Web server to sit behind an ELB thus allowing us to use Autoscaling. My question however is how to we replicate the web app across instances? Say for example we have two web servers running and we need to make a critical update to the web app, ultimately we would only want to upload to one instance and not both.

Is it even best practice to store your web app on the instance or are there better ways to store and share the app between instances?