exprimental non-prod test of encapsulating a single php-fpm pool in a systemd unit template

php7.4-fpm@.service

[Unit]
Description=The PHP 7.4 FastCGI Process Manager for %I
Documentation=man:php-fpm7.4(8)
After=network.target

[Service]
Type=notify
PIDFile=/run/php-fpm/%i/main.pid
ExecStart=/usr/sbin/php-fpm7.4 --nodaemonize --fpm-config /etc/php/7.4/fpm/sites/%i/php.conf --php-ini /etc/php/7.4/fpm/sites/%i/php.ini --pid /run/php-fpm/%i/main.pid --force-stderr
ExecReload=/bin/kill -USR2 $MAINPID

StandardOutput=journal
StandardError=journal

User=www-data
Group=www-data
WorkingDirectory=/var/www/%i
Environment=HOME=/var/www/%i
Environment=TEMP=/var/lib/php-fpm/%i/tmp TMP=/var/lib/php-fpm/%i/tmp TMPDIR=/var/lib/php-fpm/%i/tmp

TemporaryFileSystem=/var:ro
InaccessiblePaths=/boot /boot /home /lost+found /media /mnt /opt /root /srv

TemporaryFileSystem=/run/php-fpm:ro
BindPaths=/run/php-fpm/%i
RuntimeDirectory=php-fpm/%i
ReadWritePaths=/run/php-fpm/%i

TemporaryFileSystem=/var/lib/php-fpm:ro
BindPaths=/var/lib/php-fpm/%i
StateDirectory=php-fpm/%i/sessions
ReadWritePaths=/var/lib/php-fpm/%i/sessions
StateDirectory=php-fpm/%i/tmp
ReadWritePaths=/var/lib/php-fpm/%i/tmp

TemporaryFileSystem=/etc/php/7.4/fpm/sites:ro
BindPaths=/etc/php/7.4/fpm/sites/%i
ConfigurationDirectory=php/7.4/fpm/sites/%i
ReadOnlyPaths=/etc/php/7.4/fpm/sites/%i

#TemporaryFileSystem=/var/www:ro
BindPaths=/var/www/%i
ReadWritePaths=/var/www/%i

ProtectSystem=strict
PrivateUsers=yes
ProtectHostname=yes
ProtectClock=yes
ProtectKernelTunables=yes
ProtectKernelModules=yes
ProtectKernelLogs=yes
ProtectControlGroups=yes
PrivateDevices=yes
ProtectHome=yes
ProtectProc=invisible
PrivateTmp=yes
RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
MemoryDenyWriteExecute=yes
RestrictSUIDSGID=yes

[Install]
WantedBy=multi-user.target

rainloop-webmail.conf

[global]
error_log = syslog

[rainloop-webmail]
prefix = /var/www/rainloop-webmail
chdir = /var/www/rainloop-webmail/htdocs
listen = /run/php-fpm/$pool/main.sock
listen.owner = www-data
listen.group = www-data
listen.mode = 0666
catch_workers_output = yes
decorate_workers_output = no

pm = dynamic
pm.max_children = 25
pm.start_servers = 2
pm.min_spare_servers = 2
pm.max_spare_servers = 15
pm.max_requests = 512

clear_env = no
env[HOME] = /var/www/$pool

php_admin_value[upload_max_filesize] = 32M
php_admin_value[post_max_size] = 32M
php_admin_value[error_reporting] = E_ALL
php_admin_value[session.save_path] = /var/lib/php-fpm/$pool/sessions