Zammad Community sporadic Error 405 Not Allowed behind Synology nginx Reverse Proxy

Question

This morning I get sometimes irregularly the 405 Not Allowed error message on my Zammad Community App !

== Info

• Ubuntu 20.04LTS
• Apache/2.4.41
• Zammad Community 3.4.x
• ElasticSearch 7.8.1 Deb
• Synology DSM 6.2.3.25426

== Error details

Error 405 on modal with the tag <center>nginx</center> in response.

It is, weird because I am using Apache and not nginx.

== Apache conf

Listen 4000

<VirtualHost *:4000>

    ServerName        int-srv-1

    HostnameLookups   Off
    UseCanonicalName  Off
    ServerSignature   Off

    ProxyRequests     Off
    ProxyPreserveHost On

    <Proxy int-srv-1:3000>
        Require local
    </Proxy>
    
    ProxyPass /assets !
    ProxyPass /favicon.ico !
    ProxyPass /robots.txt !
    ProxyPass /ws ws://127.0.0.1:6042/
    ProxyPass / http://127.0.0.1:3000/

    DocumentRoot "/opt/zammad/public"

    <Directory "/">
        Options FollowSymLinks
        AllowOverride None
    </Directory>

    <Directory "/opt/zammad/public">
        Options FollowSymLinks
    Require all granted
    </Directory>

</VirtualHost>

But we use a "built-in" Reverse Proxy running our Synology NAS called "App Portal" to access this awesome helpdesk from outside the network (with fixed IP) available at https://hello.ourdomain.ext as the following :

== Synology NAS conf

So, I think Synology is answering this Error message because it uses nginx (I believe).

But Why?

Does HSTS or HTTP/2 could help ?

Answer 1

For the moment, a workaround seems to work.

The increase of timeout from 60 to 120sec on the advanced proxy options (Reverse Proxy Rules > Advanced Settings) seems to be paying off.