Contact Akamai who recently bought the DDOS mitigation service Prolexic. They may be able to mitigate the attack and save you bandwidth costs. Alternatively, call CloudFlare. Don't just absorb this through Amazon.
CloudFlare is probably not a good choice. They recently blocked access to a similar service, Lantern, per the linked WSJ article. "CloudFlare, which offers content-delivery network services, said last week it cut off Lantern’s use of the service, saying it was unauthorized. “We don’t do anything to thwart the content restrictions in China or other countries,” said Matthew Prince, chief executive of CloudFlare. “We’re…
I might have to reconsider mine and my clients choice of providers for this very purpose.