> On Aug 9, 2015, at 8:08 PM, Brian Geffon <briangef...@gmail.com> wrote: > > All, > We currently support strict and timed round robin for round robin DNS > records and I'd like to propose adding consistent hashing based DNS > selection. We're trying to replace our current ATS -> Haproxy setup with > only ATS and that's been the motivation behind all of our recent HostDB > improvements because we (and many others) use Haproxy simply for load > balancing / host selection. > > I've been hacking around with a few ideas and implementation methods but > basically here is what I have so far: > > 1) Add a new records.config called called > proxy.config.hostdb.consisent_hash of type INT which will enable / disable > the feature. > > 2) Add a new records.config option called > proxy.config.hostdb.consistent_hash_selection of type STRING, this will be > how the string is assembled to produce the hash. After bouncing a few ideas > around I was thinking a subset of the custom log format strings make the > most sense ( > https://docs.trafficserver.apache.org/en/latest/admin/event-logging-formats.en.html), > so basically you would do something like: > > CONFIG proxy.config.hostdb.consistent_hash_selection STRING %<cqup> > %<{X-Foo-Header}cqh> > > This would hash based on the pre-remapped request path and an incoming > header called "X-Foo-Header." Reusing this existing syntax seemed to make > the most sense. Additionally, because cookies are typically a good way to > uniquely identify a session I'll likely add another format which will get > the value of an individual cookie, is this something people would find > useful?
I kinda like the idea of using logging formats to construct the hash key. My concern is that we get yet another balancing mechanism that is similar but different. I don't really see why this is tied into hostdb. Surely the right approach is to construct a set of candidates (using hostdb, static configuration, plugin APIs, etc), and then have a single place that applies the balancing policy? > > I'd really love feedback before I land the patch. Thoughts? > > Thanks, > Brian
