UDP socket closes after first invocation

My nginx config file calls my lua file with rewrite_by_lua_file /etc/nginx/conf.d/start.lua;

The start.lua application then calls the main app that I have:

package.path = package.path .. ';/path/to/app/?.lua'
local app = require('app.init');
runtime.start();

This application has the hierarchy of

clients/
    metrics.lua
   ...
config.lua
init.lua

In the metrics.lua I instantiate a socket using

local socket = ngx.socket
local udp = socket.udp()
local ok, err = udp:setpeername(config.host, config.port)
local metrics = {}

function metrics.incSomeMetric ...

And I use udp:send when I call my metric publisher to send publish metrics to my datadog agent. All works fine on the first invocation. But any subsequent invocation givers me: 16950#0: *14 attempt to send data on a closed socket

If I collapse all the lua files into a single file inside /etc/nginx/conf.d/start.lua;, everything works fine. Seems like udp connection is closed, but upon more requests, the metrics.lua has already been loaded, so the udp:setpeername is not called again.

My work around right now is to actually have

-- metrics.lua

function _get()
    local udp = socket.udp()
    local ok, err = udp:setpeername(config.host, config.port)
    return udp
end

function metrics.incSomeMetric()
    local s = _get()
    s:send(...)
    s:close()
end

So every time I call my metric, I'm creating a new connection, sending my metric, and closing it. Is this normal? Am I doing something wrong?

I realize that from https://github.com/openresty/lua-nginx-module#udpsockclose, it mentions that the socket is closed when http request completes. My issue is /etc/nginx/conf.d/start.lua; doesn't seem to bootstrap everything the second time. I tried to add logger inside all of my files, and they are all called just ONCE after nginx service restarts. I can make as many curl requests as I want, but I only get one logger information.

In my real case example, within one http request, I may call the metrics agent a few times to publish different metrics. So I don't want to create/close a socket n times per request.

Start with the issue's start.lua and metrics.lua flow, then read the lua-nginx-module udpsockclose documentation linked in the report. Trace when rewrite_by_lua_file, require('app.init'), and udp:setpeername are invoked across requests. Done means the socket lifecycle and a supported way to reuse it for multiple metrics in one request are clearly established.