This sample demonstrates how to use Redis to route incoming requests to different HTTP backends based on the requests' User-Agent header.

This demo uses the components Lua Nginx Module and Lua Resty Redis Library enabled by default in OpenResty.

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

worker_processes  2;
error_log logs/error.log info;

events {
    worker_connections 1024;
}

http {
    server {
        listen 8080;

        location / {
            resolver 8.8.4.4;  # use Google's open DNS server

            set $target '';
            access_by_lua '
                local key = ngx.var.http_user_agent
                if not key then
                    ngx.log(ngx.ERR, "no user-agent found")
                    return ngx.exit(400)
                end

                local redis = require "resty.redis"
                local red = redis:new()

                red:set_timeout(1000) -- 1 second

                local ok, err = red:connect("127.0.0.1", 6379)
                if not ok then
                    ngx.log(ngx.ERR, "failed to connect to redis: ", err)
                    return ngx.exit(500)
                end

                local host, err = red:get(key)
                if not host then
                    ngx.log(ngx.ERR, "failed to get redis key: ", err)
                    return ngx.exit(500)
                end

                if host == ngx.null then
                    ngx.log(ngx.ERR, "no host found for key ", key)
                    return ngx.exit(400)
                end

                ngx.var.target = host
            ';

            proxy_pass http://$target;
        }
    }
}

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 Lua Resty Redis Library's README.

Before you benchmarking your interface defined here, please ensure that you've raised the error log level to warn or notice in your nginx.conf file, as in

error_log logs/error.log warn;

because flushing error log is a very expensive operation and can hurt performance a lot.