poc of openresty config to dynamically route udp traffic to backends with ip whitelisting, based upon data stored in redis

nginx.conf

worker_processes  1;
error_log logs/error.log;
events {
    worker_connections 1024;
}

stream {

 lua_shared_dict config 10m;

 init_worker_by_lua_block {
   local config = ngx.shared.config
   config:set("serverport", 0)

   local function redis_config_fetcher (called_premature)
      if called_premature then
         return
      end
      local redis = require "resty.redis"
      local cjson = require "cjson"
      local config = ngx.shared.config
      local red = redis:new()
      red:set_timeout(1000)
      local ok, err = red:connect("127.0.0.1", 6379)
      if not ok then
         ngx.log(ngx.ERR, err)
         return
      end
      local hkey
      for inport=20001,20003,1 do
        hkey = "target:"..inport
        local result, err = red:hmget(hkey,"host","port","allowip")
        if not result then
          ngx.log(ngx.ERR, err)
          break
        end
        -- set shared dict
        local hostsuccess, hosterr, hostforcible = config:set(hkey..":host", result[1])
        local portsuccess, porterr, hostforcible = config:set(hkey..":port", result[2])
        local allowipsuccess, allowiperr, allowipforcible = config:set(hkey..":allowip", result[3])
        -- check dict set success?
      end
      local ok, err = red:close()
   end

   local handle, err = ngx.timer.every(5, redis_config_fetcher)
 }


 upstream test_backend_1 {
   server localhost:10000;
   balancer_by_lua_block {
     local balancer = require "ngx.balancer"
     local host = "127.0.0.1"
     local port = 10000
     local config = ngx.shared.config
     local myport = ngx.var.server_port
     local key = "target:"..myport
     local targethost, flags = config:get(key..":host")
     local targetport, flags = config:get(key..":port")
     local ok, err = balancer.set_current_peer(targethost, targetport)
     if not ok then
       ngx.log(ngx.ERR, "failed to set peer: ", err)
       return ngx.exit(ngx.ERROR)
     end
  }
 }

  server {
   listen 20001 udp;
   listen 20002 udp;
   listen 20003 udp;
   preread_by_lua_block {
     local config = ngx.shared.config
     local myport = ngx.var.server_port
     local key = "target:"..myport
     local targetallowip, flags = config:get(key..":allowip")
      if ngx.var.remote_addr ~= targetallowip then
        ngx.exit(ngx.ERROR)
      end
   }
   proxy_pass test_backend_1;
  }

}