nginx use of UDP ports?

[Vadim Grinshpun]

On 6/12/19 4:31 AM, Maxim Dounin wrote:
> Hello!
Hi! Thanks for responding.
> On Mon, Jun 10, 2019 at 03:59:46PM -0400, Vadim Grinshpun via nginx wrote:
>
>> After setting up nginx to run, I've noticed that 'lsof' shows all nginx
>> processes (master + workers) listening on an ephemeral UDP port.
>>
>>      nginx 25142   vgrinshp    4u  IPv4 422450236      0t0  UDP
>>      127.0.0.1:33226
>>      nginx 25144   vgrinshp    4u  IPv4 422450236      0t0  UDP
>>      127.0.0.1:33226
>>      nginx 25145   vgrinshp    4u  IPv4 422450236      0t0  UDP
>>      127.0.0.1:33226
>>      nginx 25146   vgrinshp    4u  IPv4 422450236      0t0  UDP
>>      127.0.0.1:33226
>>      nginx 25147   vgrinshp    4u  IPv4 422450236      0t0  UDP
>>      127.0.0.1:33226
>>
>>
>> I did not explicitly configure anything that (AFAIK) uses UDP, and I
>> could not find anything in the doc that mentions any use of UDP ports by
>> nginx.
>> The ports seem to be used by nginx even with the most minimal nginx.conf.
>>
>> Does anyone here know how/why these ports are used?
> By default nginx doesn't use any UDP ports.  What's in your
> config?
>
Thanks for confirming this.

I was able to find the culprit on my end (a custom module that uses a 
library that, as it turns out, listens on a UDP port for tracing purposes).

-Vadim