Is it feasible (financially) to host centralised mercurial repositories on Amazon S3. As far as i can see, just by buying an S3 account, and a domain name, i could essentialy use it as a remote server. On the basis that its 0.15 dollars per month per gb and and all of my repos together probably come to less than 300mb that would make it ridiculously cheap... or am i missing something?
No. You are not. I do not know what you consider cheap, but I am using it and getting billed 1.6$ occationally. I have a large backup placed there. Just try it an risk the 2$ or so.
Btw. I suggest using the S3Organizer, which is a FireFox extension.
It's possible but you'll lose some speed/efficiency versus hosting it somewhere you can run executables. Mercurial has server side code that gets executed during clone, push, and pull. In a normal setup you trigger that remote execution by running a cgi or wsgi over http or by running the hg executable over ssh. Neither of those are available over S3.
There are, however, a few ways you could get around that limitation. One has more restrictions and one requires more setup:
Option one is to s3put the repo up there and access it via http-static://
URLs, which is a read-only fallback mode that mercurial offers. It's not very efficient, and as mentioned, it's read-only.
Option two is to mount s3 on your local filesystem using something like s3fs or fuse.
In neither case would Mercurial's nifty web interface be available from s3.