Hi Thierry,
I tried the following code to find the metatable you suggested:
haproxy.cfg:
global
lua-load /etc/haproxy/test.lua
test.lua:
core.register_init(function ()
core.Alert('--- _G ---')
for k in pairs(_G) do
core.Alert(tostring(k))
end
core.Alert('--- core ---')
for k in pairs(core) do
core.Alert(tostring(k))
end
end)
Unfortunately there is no meta_converter or similar I could use to access
converters.
Regarding the second approach: I have never made a Lua C module but I will
give it a try.
Thank you for your help!
BR,
Gabor
On Fri, Mar 24, 2017 at 7:09 PM, <[email protected]> wrote:
> On Fri, 24 Mar 2017 17:32:53 +0100
> Gabor Lekeny <[email protected]> wrote:
>
> > Hi!
> >
> > We have been using haproxy for many years and recently I found that it
> > is possible to use Lua to dynamically configure it. That is great!
> >
> > I would like to create a service which balances the HTTP requests on
> > many servers without passing through the traffic on the proxy: actually
> > it would redirect (HTTP 3xx) to the target server. As server status is
> > available in haproxy (core.proxies[backend].servers), only the balance
> > algorithm is needed to select an alive server for redirection. I could
> > not find any solution to get the server id or name after balance
> > algorithm (eg. balance uri) runs without sending the request to the
> > selected server.
> >
> > That is why I thought about to implement the balancing in Lua but
> > converters like crc32 or djb2 are not available in init (or I have not
> > found how to access them). I would like to precalculate server hashes in
> > init (for consistent hash) and not in runtime.
> >
> > Is there a way to get the backend id or name without proxying the
> request?
> > Are converter functions available in init phase?
>
>
> Hi, Maybe I'm wrong, but it seems that the server is choosed after the
> Lua executions (action or sample fetch), so it is not possible to known
> the chossen serveur during Lua phase.
>
> In other way, the choice of the server is not easy and it is not easiy
> predictible.
>
> The converters are static functions, and they can run during the init
> phase, but there are not accessible. Maybe it have an ugly solution
> that consist to create a fake object Converter and use it. The
> following code is just a guideline, it is not tested, and the Lua
> syntax is not checked.
>
> -- Get the metable of converters searching in in the Global object
> -- I assume the variable meta_converter contains this metatable
> meta_converter = ...
>
> -- Create new object which is an array containing specific content
> -- in the slot "0"
> convs[0] = 0
> set_metatable(convs, meta_converter)
>
> -- Now conv is a Converter object, and maybe it can execute some
> -- converters.
> convs:crc32("test")
>
> I'm afraid that this method doesn't work or in the worst case produce
> segfault, but you can try.
>
> In other way, if you are able to procude some line of C, you can export
> the hash function from haproxy in a file. These function are autonomous
> and doesn't have dependencies. You create your own Lua library
> containing these two functions. You will find easyly tutorials.
>
> BR,
> Thierry
>
>
> > Thanks in advance.
> >
> > BR, Gabor
> >
> >
> >
>
