Retry for idempotent backends

This is partly a FAQ, but hopefully it goes beyond that…into a more subtle FAQ, perhaps.

I understand that in general it is dangerous for haproxy to retry a request once it has been sent to a server, for example after a timeout or error, because the server may not be idempotent. I understand this objection.

However there are some backends that are designed to be idempotent, or where the consequences of retrying an operation are less bad than the consequences of clients timing out. I have servers supporting an AJAX API over HTTP which are designed in this way, partly because HTTP client retries can result in duplicate POST requests.

It would be lovely if there was an option to retry in such situations, with suitable caveats.

I would probably suggest taking this to the mailing list as a feature request.