Help with chaining of sub-requests

[agentzh]

On Tue, Apr 17, 2012 at 5:51 AM, Ashish S <ashishs.dev at gmail.com> wrote:
>
> I have 3 existing http backend web-services  S1, S2 and S3.  I am
> trying to use nginx for a use-case where  i need to first get a "key"
> from service S1, use this key along with some input data, to query S2,
> and based on S2's response, query S3.    My question is, would
> sub-request chaining be the best method to go about this?  I can use
> the upstream method to connect to S1.   Am i doing something wrong, if
> I then fire a sub-request (request to S2) from within the content
> handler (process header) method registered for this upstream?.  How do
> i then initiate the sub-request to S3 ?
>
> Any pointers or example that i might be able to follow, for something
> like the above?
>

Regarding chained subrequest implementation, see ngx_echo module's
echo_subrequest directive for an example:

   http://wiki.nginx.org/HttpEchoModule#echo_subrequest

Also ngx_lua's ngx.location.capture() and ngx.location.capture_multi()
worth a look too:

    http://wiki.nginx.org/HttpLuaModule#ngx.location.capture
    http://wiki.nginx.org/HttpLuaModule#ngx.location.capture_multi

Regarding non-subrequest upstream communication, ngx_lua supports the
cosocket API which implements something similar to (but more general
than) ngx_http_upstream:

    http://wiki.nginx.org/HttpLuaModule#ngx.socket.tcp

Hope these helps,
-agentzh