I was chatting with Kevin Boyd (aka Beryllium) on the ##aws Freenode IRC channel about the challenge of invalidating a large number of CloudFront objects (35,000) due to a problem where the cached copies of the objects were out of date and the system had not been designed with versioning in the object path or name.
In addition to the work to perform all of these invalidations (in batches of up to 1,000 in each request with at most 3 request outstanding) there is also the issue of cost. The first thousand CloudFront invalidations are free in a month, but the remainder of the invalidations in this case would cost $170 (at $0.005 for each object).
It occurred to me that one could take advantage of the on-demand nature of AWS by using the following approach: