On Thu, Apr 8, 2010 at 3:09 AM, Harmer, Sean <seanharmer@gmail.com> wrote:
> NGINX Team,
>
> Is there a way to capture the User-Agent from an HTTP Header, then query a
> database for that User-Agent, then based on the result of the database
> query, transparently route the request to an appropriate server?
>

I've got a sample app running to demonstrate this, using our
opensource modules ngx_redis2, ngx_lua, and ngx_set_misc:

https://github.com/agentzh/redis2-nginx-module

http://github.com/chaoslawful/lua-nginx-module

https://github.com/agentzh/set-misc-nginx-module

Here's the complete code listing for my nginx.conf:

worker_processes 1;
error_log logs/error.log info;
events {
worker_connections 1024;
}
http {
upstream apache.org {
server 140.211.11.131;
}

upstream nginx.org {
server 206.251.255.63;
}

server {
listen 8080;

location = /redis {
internal;
set_unescape_uri $key $arg_key;
redis2_query get $key;
redis2_pass 127.0.0.1:6379;
}

location / {
set $target '';
access_by_lua '
local key = ngx.var.http_user_agent
local res = ngx.location.capture(
"/redis", { args = { key = key } }
)

print("key: ", key)

if res.status ~= 200 then
ngx.log(ngx.ERR, "redis server returns bad status: ",
res.status)
ngx.exit(res.status)
end

if not res.body then
ngx.log(ngx.ERR, "redis returned empty body")
ngx.exit(500)
end

-- we can use the lua-redis-parser library to
parse the reply
-- here instead
local server = string.match(res.body,
"^$%d+\\r\\n(%S+)\\r\\n")
if not server then
ngx.log(ngx.ERR, "bad redis response: ", res.body)
ngx.exit(500)
end

print("server: ", server)

ngx.var.target = server
';

proxy_pass http://$target;
}
}
}

This version is longer than the one using ngx_eval, but with much
saner error handling.

And then let's start the redis server on the localhost:6379:

./redis-server # default port is 6379

and feed some keys into this using the redis-cli utility:

$ ./redis-cli
redis> set foo apache.org
OK
redis> set bar nginx.org
OK

And then let's test our nginx app!

$ curl --user-agent foo localhost:8080
<apache.org home page goes here>

$ curl --user-agent bar localhost:8080
<nginx.org home page goes here>

To further tune the performance, one could enable the connection pool
for the redis connections, as documented in ngx_redis2's README.

You can consider using the ngx_openresty bundle to run this sample to
eliminate all the pain involved in downloading and enabling 3rd-party
modules by yourself ;)

http://openresty.org/

Regards,
-agentzh

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