In these last days, we’ve finished moving an existing web site to a new server which was running IIS 7.5. This site had an upload service which used streaming for allowing the upload of some interestingly sized files. We’ve already had it running without any problems in IIS 6 and 7 (though in this case, we tested it using Windows 7), so it was a surprise to see that nobody could make an upload after the migration. The streaming service was returning the 413.Request Entity Too Large.
After some digging, I’ve managed to find a discussion in the IIS Forums which suggested that the problem was related with the uploadReadAheadSize attribute of the serverRuntime element. And sure enough, changing its default value in the apphost config file solved this problem because we were using SSL and that means the request entity body must be preloaded (and when that happens, the SSL preload will use that value for doing its thing).