Hi Chris, On Tue, Jan 06, 2026 at 09:13:02PM +0000, Christopher Staite wrote: > Hi, > > I've been looking into the powerful set-dst feature to enable cross-cluster > forwarding. I'd like to have a fallback in case a region has gone down for > some reason or another. However, I'm struggling to get it to work with > retry-on or redispatch. > > I've been trying something like: > > backend b > mode http > option redispatch > http-request set-var(txn.target_host) req.hdr(Host),lower,field(1,:) > http-request do-resolve(txn.target_ip,dns) var(txn.target_host) > http-request set-dst var(txn.target_ip) > http-request set-dst-port int(443) > server forward 0.0.0.0:0 ssl verify required ca-file @system-ca sni > req.hdr(host) > server fallback 127.0.0.1:80 > > However, I end up with an SH-- on failure. I also tried with retry-on, > setting a session variable on http-request and then set-dst 127.0.0.1 if the > session variable is set. > > I feel like there must be a way to do this, but after a few hours of pouring > over the docs and trying things out I think I've come to the conclusion that > it's not possible. > > Hopefully someone can give me an insight in to whether this is actually > impossible or if I'm missing something obvious.
I'm not really seeing any way to do this, because the load balancing is applied to choose a server based on the LB algorithm, then the connection is attempted, then in case of failures the retries happen, and for the last retries (or after a configurable set), the redispatch happens, which consists in applying the LB algo again, and since there's no way to check the remote server, I don't see how we could choose another server without that server being selected as well under normal conditions. Hmmm wait a minute, maybe the "balance first" algo could do it. I'm seeing that it supports the ability to avoid the previously attempted server in case of redispatch, and since you cannot enable health checks, I think it should always select your first server, except for redispatch. So you could try to add just this line to your config and see if it works. And if it does, it would be nice to append this to the doc and mention it there, since right now the doc says that "balance first" only makes sense with a configured maxconn (to deal with overload) but here that would be a different use case. I don't promise anything though, so please try first ;-) Willy
