Two PHP versions

This recipe is for a host running two php-fpm masters, here php8.3-fpm and php8.4-fpm on Debian or Ubuntu, with pool directories /etc/php/8.3/fpm/pool.d and /etc/php/8.4/fpm/pool.d. It ends with two daemons, one per master, each with its own budget.

Why one daemon must not see both

Unscoped, fpm-tune plan plans both masters' pools as one host and sudo fpm-tune apply refuses, naming every master and pid and asking for --drop-in-dir. Pools that share a name (www in both) cannot be told apart in the metrics either.

Scoping fixes the writing, and creates a budget problem. Each daemon reads its own master's memory limit, and with no cgroup limit that is the whole host from /proc/meminfo. Two daemons that each budget 85% of the same memory can commit more than the host has. So the budget is split first, by giving each master its own cgroup limit, and each daemon then sizes inside its master's limit.

1. Split the budget

Decide how much of the host each PHP version may use, and set it on the units. This takes effect live and survives reboots:

sudo systemctl set-property php8.3-fpm.service MemoryMax=2G
sudo systemctl set-property php8.4-fpm.service MemoryMax=4G

A scoped daemon reads the limit from its master's cgroup, so each budget starts from its own number. The alternative is --memory 2G on one daemon and --memory 4G on the other; that sizes against the number you gave without subtracting other services, and the kernel enforces nothing. The budget explains the difference.

2. Turn on the status pages, per master

sudo fpm-tune enable-status --drop-in-dir /etc/php/8.3/fpm/pool.d
sudo fpm-tune enable-status --drop-in-dir /etc/php/8.4/fpm/pool.d

Each writes zz-fpm-tune-status.conf into its own pool directory and reloads its own master.

3. Plan each master

fpm-tune plan --drop-in-dir /etc/php/8.4/fpm/pool.d

The first line of the budget block reads php-fpm's memory 4.0GiB rather than host memory, which confirms the daemon is sizing inside the cgroup limit. Repeat for 8.3.

4. Install the first daemon

install-service installs exactly one unit, fpm-tune.service, reading /etc/fpm-tune/config. Install it, then scope it to 8.4 by setting drop-in-dir in the config (the key is present, commented out) and restarting:

sudo fpm-tune install-service
sudo sed -i 's|^# drop-in-dir =.*|drop-in-dir = /etc/php/8.4/fpm/pool.d|' /etc/fpm-tune/config
sudo systemctl restart fpm-tune

This daemon keeps the defaults: state at /var/lib/fpm-tune/state.json, control socket beside it, backups under /var/lib/fpm-tune/backup, metrics on 127.0.0.1:9110.

5. Write the second daemon's config and unit

The second daemon needs its own state file (a daemon holds the state lock for its lifetime, so two cannot share one), its own control socket, backup directory, metrics port and recommendation file. Any serve flag is a config key:

sudo tee /etc/fpm-tune/config-8.3 >/dev/null <<'CONF'
mode = advisory
metrics = 127.0.0.1:9111
drop-in-dir = /etc/php/8.3/fpm/pool.d
state = /var/lib/fpm-tune-8.3/state.json
control = /var/lib/fpm-tune-8.3/control.sock
backup-dir = /var/lib/fpm-tune-8.3/backup
recommend = /var/lib/fpm-tune-8.3/recommended.conf
CONF

The unit is the one install-service --print shows, with the paths and the php-fpm unit changed:

sudo tee /etc/systemd/system/fpm-tune-8.3.service >/dev/null <<'UNIT'
[Unit]
Description=fpm-tune for php8.3-fpm
Wants=php8.3-fpm.service
After=php8.3-fpm.service

[Service]
ExecStart=/usr/local/bin/fpm-tune serve --config /etc/fpm-tune/config-8.3
Restart=on-failure
RestartSec=5
StateDirectory=fpm-tune-8.3
StateDirectoryMode=0700

[Install]
WantedBy=multi-user.target
UNIT
sudo systemctl daemon-reload
sudo systemctl enable --now fpm-tune-8.3
journalctl -u fpm-tune-8.3 -f

The lock that serialises writers lives under /run/fpm-tune and is keyed on the pool directory, so the two daemons never block each other. A stray sudo fpm-tune apply beside them is refused by the state lock the first daemon holds; ask a daemon with apply-now instead.

6. Operate them

mode, top and apply-now default to the installed service. For the second daemon, name its endpoints:

fpm-tune top --addr 127.0.0.1:9111
sudo fpm-tune apply-now --control /var/lib/fpm-tune-8.3/control.sock

fpm-tune mode only rewrites /etc/fpm-tune/config, so switch the second daemon by editing mode in /etc/fpm-tune/config-8.3 and running sudo systemctl restart fpm-tune-8.3. Point Prometheus at both ports; the series are the same, one set per daemon.