PHP_EXTENSIONS environment variable does not install extensions at runtime

[rdehnhardt]

Summary

The PHP_EXTENSIONS environment variable is accepted by the container but does not actually install the specified extensions at startup.

Environment

• Image: serversideup/php:8.5-fpm-nginx
• Platform: macOS (Apple Silicon) / Docker Desktop
• Docker Compose with dev override

Steps to Reproduce

1. Set PHP_EXTENSIONS: "intl pcov" in docker-compose.dev.yml environment:

# docker-compose.dev.yml
services:
  app:
    image: serversideup/php:8.5-fpm-nginx
    environment:
      AUTORUN_ENABLED: false
      PHP_OPCACHE_ENABLE: "0"
      PHP_DISPLAY_ERRORS: "On"
      PHP_EXTENSIONS: "intl pcov"
    volumes:
      - .:/var/www/html

2. Start the container with docker compose -f docker-compose.yml -f docker-compose.dev.yml up -d
3. Verify with php -m | grep pcov — extension is not loaded
4. Verify with env | grep PHP_EXTENSIONS — variable is present

Expected Behavior

Extensions listed in PHP_EXTENSIONS should be installed via install-php-extensions during container startup, similar to how other environment variables (e.g., PHP_OPCACHE_ENABLE, PHP_MEMORY_LIMIT) are applied at runtime.

Actual Behavior

The environment variable is set inside the container but the extensions are never installed. No error messages appear in the container logs. Manual installation with install-php-extensions pcov (as root) works correctly.

Workaround

Using a custom Dockerfile that bakes the extensions into the image:

FROM serversideup/php:8.5-fpm-nginx

USER root
RUN install-php-extensions intl pcov
USER www-data

Suggestion

It would be useful to have runtime extension installation via an environment variable (e.g., PHP_EXTENSIONS) that runs install-php-extensions during the container entrypoint, before the main process starts. This would allow developers to add extensions without maintaining a custom Dockerfile, especially useful in development environments where build time matters less than convenience.