As I was looking on: https://hub.docker.com/_/php/ I have seen images tagged as:
version_number-zts-alpine and I am wondering what does the zts indicate on these tags and how much different are from fpm or Apache images?
If you read one of the docker files https://github.com/docker-library/php/blob/1e6f8ba4901a5f3f02f447fd70d4226193e4f24b/7.2-rc/zts/Dockerfile for example. This has
ENV PHP_EXTRA_CONFIGURE_ARGS --enable-maintainer-zts
This is used to enable the Zend Thread Safety package in PHP which is used for pthreads. From the PHP manual(http://php.net/manual/en/pthreads.requirements.php)
pthreads requires a build of PHP with ZTS (Zend Thread Safety) enabled
( –enable-maintainer-zts or –enable-zts on Windows )
Regarding the zts itself is something related to pthreads where you can look for more information on Php: when to use pthread