In PHP 7.2.0 a change [1] was made in response to bug [#74166] to fall
back to listening on 0.0.0.0 if IPv6 is disabled (for example with
ipv6.disable=1 Linux kernel param) instead of failing to create a
listening socket with the error "Address family not supported by
protocol (97)".
A fallback to IPv4 in such circumstances is only possible in PHP >=
7.2.0 and by specifying a port number without an address to the listen
directive.
[1]: b63c45c69e
[#74166]: https://bugs.php.net/bug.php?id=74166
This will hopefully help folks with the confusion around installing packages like "php-apcu" and then wondering why they don't actually "work" (because they pull in Debian's PHP, and that's not what this image packages).
