Hi Robin. Am 29.10.2018 um 20:15 schrieb Robin H. Johnson: > On Sat, Oct 27, 2018 at 01:52:29PM +0200, Aleksandar Lazic wrote: >>> Right now, if you want to use load feedback for weights, you either need >>> something entirely out-of-band from the servers back to HAProxy, or you >>> have to use the agent-check option and run a separate health agent. >> >> With that you mean "external-check command" ? >> >> https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#external-check%20command > No, I mean 'agent-check' per > https://cbonte.github.io/haproxy-dconv/1.8/configuration.html#5.2-agent-check > > This is an agent that runs on the realserver, not the load balancer.
Thanks for clarification. > ... >>> I would like to propose a new http-agent-check option, with two usage >>> modes. >>> 1. health-check mode: this connects like the existing agent-check, but >>> sends does HTTP request & response rather than pure TCP. >>> >>> 2. inline mode: if the server has best-case knowledge about it's status, >>> and HTTP headers are used for the feedback information, then it >>> should be possible to include the feedback in an HTTP response header >>> as part of normal queries. The header processing would detect & feed >>> the data into the health system during normal traffic. >> >> Interesting Ideas. >> Are there any LB's out there which already uses this concept? > I haven't looked specifically, but I am aware of a lot of other > dynamic-realserver weight work (mostly in the keepalived/ipvs world, > like feedbackd and lvs-kiss from the early 2000's). > > The inline mode is probably deserving of seperate work, I think it might be > possible > to implement it with the existing Lua codebase. > >>> Question: where & how should the feedback information be encoded in the >>> response? >>> 1. HTTP payload >>> 2. Single HTTP header >>> 3. Multiple HTTP headers >> >> I would like to have it in the one header per value 'Server-State-*' as the >> X- >> Prefix is Deprecated. >> >> https://tools.ietf.org/html/rfc6648 >> Deprecating the "X-" Prefix and Similar Constructs in Application Protocols >> >> for example: >> Server-State-Load >> Server-State-Users >> Server-State-Health >> Server-State-... > > Multiple headers easier to write new parsers for I agree, but supporting > the other variants might be worthwhile. > > I'm thinking to maybe implement my lua-check first, then write a simple > HTTP checker within Lua. Yes sounds good. Lua is a good option IMHO. What's your opinion to use http-response with an new option set-config-value like "set-nice", as there is already the http engine which handles the http headers from the server. Naive example ### declare capture response len 5 capture response header Server-State-Load len 5 # set the weight for the current backend http-response set-config-value weight %[res.hdr(Server-State-Load),capture-res(0)] if res.hdr(Server-State-Load) ### It would be nice to make this possible as a value for peers so that all instances from a distributed haproxy setup have the same weight for this server. Regards Aleks
