How much capacity does Amazon EC2 have? And how much gets provisioned?

Given that it’s now clear that there are capacity constraints on EC2 (i.e., periods of time where provisioning errors out due to lack of capacity), this is something that’s of direct concern to users. And for all the cloud-watchers, it’s a fascinating study of IaaS adoption.

Randy Bias of CloudScaling has recently posted some interesting speculation on EC2 capacity.

Guy Rosen has done a nifty analysis of EC2 resource IDs, translated to an estimate of the number of instances provisioned on the platform in a day. Remember, when you look at provisioned instances (i.e., virtual servers), that many EC2 instances are short-lived. Auto-scaling can provision and de-provision servers frequently, and there’s significant use of EC2 for batch-computing applications.

Amazon’s unreserved-instance capacity is not unlimited, as people have discovered. There are additional availability zones, and for serious users of the platform, choosing the right zone has become minimal, since you don’t want to pay for cross-zone data transfers or absorb the latency impact, if you don’t have to.

We’re entering a time of year that’s traditionally a traffic ramp for Amazon, the fall leading into Christmas. It should be interesting to see how Amazon balances its own need for capacity (AWS is used for portions of the company’s retail site), reserved EC2 capacity, and unreserved EC2 capacity. I suspect that the nature of EC2’s usage makes it much more bursty than, say, a CDN.