What are the practical limitations with auto scaling EC2 or other cloud computing infrastructure?

Question

I was curious if anyone has experimented with auto scaling web or db tier in EC2 or other cloud computing infrastructure? It seems theoretically possible, but I am curious what the practical limitations are/maybe.

Thanks!

Answer 1

We are also starting to look at auto-scaling.

The first candidate approach is to use Amazon's ELB (Elastic Load Balancer) and Cloud Front. However, our traffic is a web service. Caller's frequently send the 100-Continue http message, and ELB cannot understand that message. There's no word yet from Amazon on when that might be fixed. Also, there are a number of complaints in the Amazon forums about ELB not handling heavy load.

LigHTTPD 1.5 looks like a promising partial solution, in that it can detect when an instance is not functioning and transparently take it out of the rotation, and can be dynamically reconfigured without restarting the load balancer.

There are a number of commercial solutions as well. We will probably have a look at Right Scale.

Answer 2

This is more of a question than an answer, but I'm about to start experimenting with autoscaling myself (most likely using the Amazon CloudFront facilities) and am thinking that instance startup time will be a factor. I've noticed that a new EC2 instance can take from 5 to 20 minutes to start up, so it's not as if you can instantly add more capacity when your load increases; it seems like you would need one or more idle instances to be running and ready to pick up increased load.

Answer 3

Late addition:

Consider SimpleDB as well... this would eliminate the DB scaling side.

For autoscaling, we rolled our own scripts to monitor, launch, and provision servers and yes, the whole process takes about 7 minutes. We do a little predictive analysis to guess when new servers will be needed and then just break them down if they aren't. Total cost: ~10 cents.

Also, Scalr looks promising as a commercial solution (haven't used it).

Chad