OpenResty config to read from redis

nginx.conf

#user  nobody;
worker_processes  5;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;


    sendfile        on;
    keepalive_timeout  65;


    server {
        listen       80;
        location / {
            resolver 8.8.4.4;  # use Google's open DNS server

            set $target '';
            access_by_lua '
                local key = ngx.var.http_user_agent
                local ngxhost = ngx.req.get_headers()["Host"]
                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(ngxhost)
                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;
        }
    }
}