Do not install everything by default.

Dockerfile

@@ -1,15 +1,5 @@
 FROM php:7.4-apache
 
-RUN apt-get -y update && \
-    apt-get -y upgrade
-
-ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
-
-RUN chmod +x /usr/local/bin/install-php-extensions && \
-    install-php-extensions gd mysqli pdo_mysql && \
-    apt-get clean && \
-    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* /usr/share/doc/*
-
 ENV APACHE_DOCUMENT_ROOT /var/www/html
 
 RUN sed -ri -e 's!/var/www/html!/var/www/html!g' /etc/apache2/sites-available/*.conf
@@ -21,13 +11,6 @@ RUN sed -ri -e 's!upload_max_filesize = 2M!upload_max_filesize = 8M!g' $PHP_INI_
 
 RUN a2enmod rewrite
 
-RUN cd ${APACHE_DOCUMENT_ROOT}
-RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
-RUN php -r "if (hash_file('sha384', 'composer-setup.php') === 'dac665fdc30fdd8ec78b38b9800061b4150413ff2e3b6f88543c636f7cd84f6db9189d43a81e5503cda447da73c7e5b6') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
-RUN php composer-setup.php
-RUN php -r "unlink('composer-setup.php');"
-RUN php composer.phar install --working-dir ${APACHE_DOCUMENT_ROOT}
-
 ARG UNAME=www-data
 ARG UGROUP=www-data
 ARG UID=1000