We’ve received an interesting tip today from someone who set up Charles as a WiFi proxy on their iPad to get a glimpse at the HTTP traffic which occurs when an image is sent through iMessage. Interestingly enough, it seems that iCloud somehow utilizes Amazon’s AWS cloud services as well as Microsoft Azure.
icloud.com provides some sort of authentication to a windows.net address, and then sends a confirmation back to iCloud. Image downloads come from an s3.amazonaws.com address. This process is visible in the screenshots above (click to enlarge).
We presume that iCloud isn’t entirely based on these other cloud services; it would be much more reasonable to deduce from these images that the other services are being used as some sort of CDN to take the load off of Apple. It’s also possible that, once iOS 5 and iCloud come out of beta and Apple’s own datacenters are completely ready, Apple will stop using these other cloud services altogether. We’ll just have to wait and see.