HAProxy - Try Multiple Backends Sequentially?

[Jason Bronnx]

Hi,

Tried to search on this for a couple of hours, but had no luck, hoping you
guys can help.

I have a use case, that I need to try the request on backend-A first, then
if returns 200, then it'll query backend-B and return that result.  If it
returns != 200, just return 404.  Something like this:

function pseudoCode() {
  if (backend-a.process() == 200) {
    return backend-b.process()
  }

  // Got a non-200 from backend-a, just return 404
  return 404
}

Is there a straightforward way of doing this in haproxy?

Thanks!
Jason