[bromley]

If you have one single instance only, I'm not sure there is any point. But if you want your app to auto-scale upwards to add EC2 instances if the load increases, then the load balancer is necessary. It enables all your EC2 instances to be accessible via one public URL (as the elastic load balancer forwards requests on).

I set it up such that we always have at least 2 EC2 instances, in separate availability zones, so that, if one goes down, at least the other is likely to keep working. And then it auto-scales upwards from there, if the load gets high enough.

The load balancer is pretty much transparent as far as you the developer is concerned. You don't need to configure it - beanstalk does that - and it scales completely transparently (unlike the EC2 instances, for which you do need to define auto-scaling rules if you want that).

I may be missing some subtleties as I'm far from being an AWS expert... Just been picking bits up here and there through using beanstalk and a few of the other APIs for extra bits and bobs.