I basically have the same problem as mentioned in this thread -- I would like to temporarily suspend all requests to all servers of a certain backend, so that I can upgrade the backend and the database it uses. Since this is a live system, I would like to queue up requests, and send them to the backend servers once they've been upgraded. Since I'm doing a database upgrade with the code change, I have to upgrade all backend servers simultaneously, so I can't just bring one down at a time.
I tried using the tcp-request options combined with removing the static healthcheck file as mentioned in that thread, but had no luck. Setting the default "maxconn" value to 0 seems to pause and queue connections as desired, but then there seems to be no way to increase the value back to a positive number without restarting HAProxy, which kills all requests that had been queued up until that point. (The "hot-reconfiguration" options using -sf and -st start a new process, which doesn't seem to do what I want).
Is what I'm trying to do possible?