Pin Debian variants to stretch for now

The plan is to switch to buster once docker-library/php#865 is resolved in a clean way (either in the PHP image or in PHP itself).

Author: tianon

7/apache/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.2-apache
+FROM php:7.2-apache-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

7/fpm/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.2-fpm
+FROM php:7.2-fpm-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

8.6/apache/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.3-apache
+FROM php:7.3-apache-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

8.6/fpm/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.3-fpm
+FROM php:7.3-fpm-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

8.7/apache/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.3-apache
+FROM php:7.3-apache-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

8.7/fpm/Dockerfile

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:7.3-fpm
+FROM php:7.3-fpm-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \

Dockerfile-debian.template

@@ -1,5 +1,6 @@
 # from https://www.drupal.org/docs/8/system-requirements/drupal-8-php-requirements
-FROM php:%%PHP_VERSION%%-%%VARIANT%%
+FROM php:%%PHP_VERSION%%-%%VARIANT%%-stretch
+# TODO switch to buster once https://github.com/docker-library/php/issues/865 is resolved in a clean way (either in the PHP image or in PHP itself)
 
 # install the PHP extensions we need
 RUN set -eux; \