While this is fascinating, and Willy is brilliant as always, I always wondered why HAProxy couldn't just, you know, reload the config.
Surely you don't need to fork: Just parse the new config, create the necessary internal data structures, and let traffic flow into the new ruleset while keeping all the sockets (except for those that are superfluous, and of course let in-flight requests finish). Is it because HAProxy's internals weren't designed to do that and that it would too big of a rewrite?
I always found Varnish's design very cool: It compiles the configuration (which is a DSL called VCL) to C and loads it as a dynamically loaded library. I don't know how it does hot reloads, but I believe it does do them seamlessly.
Surely you don't need to fork: Just parse the new config, create the necessary internal data structures, and let traffic flow into the new ruleset while keeping all the sockets (except for those that are superfluous, and of course let in-flight requests finish). Is it because HAProxy's internals weren't designed to do that and that it would too big of a rewrite?
I always found Varnish's design very cool: It compiles the configuration (which is a DSL called VCL) to C and loads it as a dynamically loaded library. I don't know how it does hot reloads, but I believe it does do them seamlessly.