I am trying to set up the farm of webservers, consisting of the internal, external and worker servers.
The actual sites content is stored on internal NFS server deep in internal network. All sites contents management is centralized.
BSD-based external servers have Lighttpd doing all the HTTP/HTTPS job, serving static content. Main NFS share is auto-mounted via special path, like /net/server/export/www/site/ (via amd).
Every Lighttpd have fastcgi parameters pointing to several worker servers, which have php-fpm working (for example). Different sites may require different php versions or arrangement, so www01 and www02 may serve site "A" having php-fpm over PHP 5.6 and www05 and www06 will serve site "B" having php-fpm over PHP 7.2.
Every worker get requests for certain sites (one or more) with path /net/server/export/www/site and execute PHP or any other code. They also have amd (for BSD) and autofs (for Linux) working.
For some sites Lighttpd may not forward fastcgi, but do proxying instead, so workers can have Apache or other web-server (even Java-based) working.
External servers are always BSD, internal servers too, but workers can be different upon actual needs.
This all work good when workers are BSD. If we are using Linux on workers - it stops working when share is automatically unmounted. When one tries to access the site he will get error 404. When I connect to server via ssh I will see no mounted share on "df -h". If I do any "ls" on /net/server/export - it is self-mounted as intended and site starts to work. On BSD-systems df show amd shares always mounted despite of 60 seconds dismount period.
I believe there is a difference between amd and autofs approach, php-fpm calls on Linux become some kind of "invisible" to autofs and do not cause auto-mount, because any other access to /net/server/ work at any time and do cause auto-mount. Also, this happens not with php-fpm only, Apache serving static content on auto-mounted NFS share behave same way.
Sorry for long description, but I tried to describe it good. The main question here - is anyone know why calls to /net/server may not cause auto-mount in autofs and how to prevent this behavior.
For lot of reasons I do not consider using static mounting, so this is not an option here. As for Linux versions - mostly it was tested on OEL 7.recent.