Dynamically set php-fpm workers in docker containers.

entrypoint.sh

#!/usr/bin/env bash

set -eo pipefail

logger() {
  printf '%s (%s) %s [%s]: %s\n' "$(date)" "$(whoami)" "${BASH_SOURCE}" "${1}" "${2}"
}

# determine maxprocs according to cgroup-mem-limit
memory_available="$(cat /sys/fs/cgroup/memory/memory.limit_in_bytes)"
memory_per_proc="$(php-memory-limit.php)"
php_num_procs="$(echo "$((memory_available / memory_per_proc))" | awk '{print int($1)}')"

logger "INFO" "memory available: ${memory_available} / memory per proc: ${memory_per_proc} / php num procs: ${php_num_procs}"

sed -i '/^pm/d' /usr/local/etc/php-fpm.d/www.conf
printf 'pm = static\npm.max_children = %d\n' "${php_num_procs}" >> /usr/local/etc/php-fpm.d/www.conf

# passthrough to original entrypoint
exec docker-php-entrypoint "${@}"

php-memory-limit.php

#!/usr/bin/env php
<?php

# https://www.php.net/manual/en/function.ini-get.php#refsect1-function.ini-get-examples
function return_bytes($val) {
    $val = trim($val);
    $mod = strtolower(substr($val, -1));
    $val = (int) substr($val, 0, -1);

    switch($mod) {
        case 'g':
            $val *= 1024;
        case 'm':
            $val *= 1024;
        case 'k':
            $val *= 1024;
    }

    return $val;
}

echo return_bytes(ini_get('memory_limit')) . PHP_EOL;