Weird behaviour for DNS resolution
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Descripción
Description
I have look on the internet and see very little talk about this so it's possible that my php is wrongly configure but I have failed to find a directive related to this.
The following code:
Not sure where the code is located, my C understanding is pretty weak and I'm an ops guy.
I think it's around here : https://github.com/php/php-src/blob/master/ext/standard/dns.c
What I see :
When a php process does a dns query for both A and AAAA type, if A is valid but AAAA is empty, both records are not stored in cache and therefor the next request will trigger a dns query for both type again.
It seems like the empty AAAA response triggers an invalidation in the cache for both A and AAAA record. This behaviour floods the network needlessly.
I have notice this behaviour both on VMs or on containers, and from a wide range of php versions (5.6 to 8.3) or OS versions (Debian 9/10/11/12, Ubuntu 16/18/20/22 or Alpine 3.18/3.19).
I can provide this graph to illustrate better what I'm saying (Yellow and Green line are AAAA and A type) :
What I would expect :
In my opinion, once a A record have been successfully retrieved, it should be stored in cache and the AAAA should not invalidate it. And maybe once the A record expires it should try again both resolution (A and AAAA).
I have tested successfully to disable ipv6 in kernel for VMs and it drastically reduces the number of DNS query sent by applications (see graph below) and looks like the A response is stored in cache. This is a possible solution for VMs but complicated one in a Kubernetes environment.
PHP Version
8.3
Operating System
No response
Guía de contribución
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Línea de trabajo
Empieza en ext/standard/dns.c y reproduce el comportamiento de PHP 8.3 con un nombre de host que tenga un registro A pero ningún registro AAAA. Traza cómo se almacenan en caché o se invalidan las respuestas A y AAAA, y luego añade o actualiza una cobertura específica para que un resultado A válido permanezca en caché cuando la respuesta AAAA esté vacía.
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Evaluación
- Stack tecnológico
- c, php
- Área
- backend, networking
- Tipo de issue
- Error
- Dificultad
- 4/5
- Tiempo estimado
- 3-5 días
- Estado de actividad
- Tranquilo
- Claridad
- Necesita aclaración
- Aptitud para principiantes
- 35/100