The original C10K problem studies how to provide reasonable service to 10,000 simultaneous clients or HTTP requests using a normal web server. I call the following problem the reverse C10K problem, or RC10K --- how to support 10,000 simultaneous outbound HTTP requests running on a web server. The RC10K problem can be found in scenarios like service orchestrations and server-side mashups. A server-side mashup needs to send several simultaneous HTTP requests to partner services for each inbound request.
Many approaches to improving the performance and scalability of HTTP servers can be applied to tackle the original C10K problem. However, whether these approaches can tackle the reverse C10K problem needs to be verified. My recent paper discussed the RC10K problem, and presented some experiment results got from a prototype mashup server application.