Weird behaviour for DNS resolution
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Description
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
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Piste de recherche
Commencez dans ext/standard/dns.c et reproduisez le comportement de PHP 8.3 avec un nom d’hôte qui possède un enregistrement A, mais aucun enregistrement AAAA. Suivez la manière dont les réponses A et AAAA sont mises en cache ou invalidées, puis ajoutez ou mettez à jour une couverture ciblée afin qu’un résultat A valide reste en cache lorsque la réponse AAAA est vide.
Rédigé par le modèle d'indexation à partir du texte de l'issue.
Évaluation
- Stack technique
- c, php
- Domaine
- backend, networking
- Type d'issue
- Bug
- Difficulté
- 4/5
- Temps estimé
- 3-5 jours
- Activité
- Calme
- Clarté
- À clarifier
- Accessibilité débutants
- 35/100