On Tue, 19 Jul 2016 15:28:25 +0530
Sachin Shetty <[email protected]> wrote:
> Hi,
>
> We always had a unique requirement of picking a backend based on response
> from a external http service. In the past we have got this working by
> routing requests via a modified apache and caching the headers in maps for
> further request, but now I am trying to simplify our topology and trying to
> get this done using just haproxy and lua.
>
> I am running in to some problems:
>
> Lua method:
>
> function choose_backend(txn)
>
> local host = txn.http:req_get_headers()["host"][0]
>
> core.Alert("Getting Info:" .. host)
>
> local sock = core.tcp()
>
> sock:connect("127.0.0.1", 6280)
>
> sock:send("GET /eos/rest/private/gds/l1/1.0/domain/" .. host ..
> "\r\n")
>
> result = sock:receive("*a")
>
> sock:close()
>
> core.Alert("Received Response:" .. result .. "<")
>
> core.set_map("/tmp/proxy_webui.map", host, result)
>
> core.Alert("Map Set:" .. host .. "-->" .. result .. "<")
>
> end
>
>
>
> core.register_action("choose_backend", { "http-req" }, choose_backend)
>
>
> Haprpxy Conf:
>
> frontend luatest
>
> mode http
>
> maxconn 10000
>
> bind *:9000
>
>
>
> use_backend %[hdr(host),lower,map(/tmp/proxy_webui.map)] if FALSE #
> To declare the map
>
>
> http-request lua.choose_backend
>
>
> tcp-request content capture hdr(host),map(/tmp/proxy_webui.map) len
> 80
>
> acl is_ez_pod capture.req.hdr(0) http://127.0.0.1:6280
>
> use_backend ez_pod if is_ez_pod
>
>
>
>
>
> backend ez_pod
>
> server ez_pod 192.168.56.101:6280 maxconn 2
>
>
>
>
>
> There are some issues:
> 1. I do see Map Set called correctly in the logs, but the haproxy capture
> does not find the key in the map for the first request. Is this related to
> async execution of luna routine?
Hi,
The processing of the request by haproxy is pending while the execution
of the lua action.
The execution of "tcp-request content" directives are done before the
execution of "http-request". So HAProxy executes first the capture and
them the action which populate the map.
Normally, HAProxy display a warning when it start, if it detects a
configuration order different than a execution order. Try to replace the
"tcp-request" by "http-request".
> 2. I expected subsequent requests to see the value atleast, but even that is
> not consistent, some request see the value in the map and some don¹t
> Is there a better way to do this?
It seems that you use a good way to do this.
> I already found that I cannot invoke the
> luna routine with use_backend because yield is not allowed in a sample fetch
> context.
Yes, the usage of core.tcp() require some yields, and haproxu doesn't
support yield during the execution of sample-fetches. For bypassing
this problem, I use variables. I store the expected result in a
variable during the execution of the action, and I use these variable
with the use_backend directive.
Thierry
> What would be the best way to achieve this, our requirement is similar to
> what can be done with redis+nginx here:
> http://openresty.org/en/dynamic-routing-based-on-redis.html except for we
> have an http service that decides the backend instead of a redis service.
>
> Thanks
> Sachin
>
>
