Add Composer Docker layer

Dockerfile

@@ -4,4 +4,56 @@
 # This helps keep ou Dockerfiles DRY -> https://bit.ly/dry-code
 # You can see a list of required extensions for Laravel here: https://laravel.com/docs/8.x/deployment#server-requirements
 ARG PHP_EXTS="bcmath ctype fileinfo mbstring pdo pdo_mysql tokenizer dom pcntl"
-ARG PHP_PECL_EXTS="redis"
+ARG PHP_PECL_EXTS="redis"
+
+# We need to build the Composer base to reuse packages we've installed
+FROM composer:2.1 as composer_base
+
+# We need to declare that we want to use the args in this build step
+ARG PHP_EXTS
+ARG PHP_PECL_EXTS
+
+# First, create the application directory, and some auxilary directories for scripts and such
+RUN mkdir -p /opt/apps/laravel-in-kubernetes /opt/apps/laravel-in-kubernetes/bin
+
+# Next, set our working directory
+WORKDIR /opt/apps/laravel-in-kubernetes
+
+# We need to create a composer group and user, and create a home directory for it, so we keep the rest of our image safe,
+# And not accidentally run malicious scripts
+RUN addgroup -S composer \
+    && adduser -S composer -G composer \
+    && chown -R composer /opt/apps/laravel-in-kubernetes \
+    && apk add --virtual build-dependencies --no-cache ${PHPIZE_DEPS} openssl ca-certificates libxml2-dev oniguruma-dev \
+    && docker-php-ext-install -j$(nproc) ${PHP_EXTS} \
+    && pecl install ${PHP_PECL_EXTS} \
+    && docker-php-ext-enable ${PHP_PECL_EXTS} \
+    && apk del build-dependencies
+
+# Next we want to switch over to the composer user before running installs.
+# This is very important, so any extra scripts that composer wants to run,
+# don't have access to the root filesystem.
+# This especially important when installing packages from unverified sources.
+USER composer
+
+# Copy in our dependency files.
+# We want to leave the rest of the code base out for now,
+# so Docker can build a cache of this layer,
+# and only rebuild when the dependencies of our application changes.
+COPY --chown=composer composer.json composer.lock ./
+
+# Install all the dependencies without running any installation scripts.
+# We skip scripts as the code base hasn't been copied in yet and script will likely fail,
+# as `php artisan` available yet.
+# This also helps us to cache previous runs and layers.
+# As long as comoser.json and composer.lock doesn't change the install will be cached.
+RUN composer install --no-dev --no-scripts --no-autoloader --prefer-dist
+
+# Copy in our actual source code so we can run the installation scripts we need
+# At this point all the PHP packages have been installed,
+# and all that is left to do, is to run any installation scripts which depends on the code base
+COPY --chown=composer . .
+
+# Now that the code base and packages are all available,
+# we can run the install again, and let it run any install scripts.
+RUN composer install --no-dev --prefer-dist