Use multi-stage build

Dockerfile

@@ -1,7 +1,6 @@
+FROM composer:1.5
 FROM php:7.1-fpm-alpine
 
-WORKDIR /srv/app
-
 RUN apk add --no-cache --virtual .persistent-deps \
 		git \
 		icu-libs \
@@ -22,17 +21,14 @@ RUN set -xe \
 	&& docker-php-ext-enable --ini-name 05-opcache.ini opcache \
 	&& apk del .build-deps
 
-###> recipes ###
-###< recipes ###
-
 COPY docker/app/php.ini /usr/local/etc/php/php.ini
+COPY --from=0 /usr/bin/composer /usr/bin/composer
+COPY docker/app/docker-entrypoint.sh /usr/local/bin/docker-app-entrypoint
+RUN chmod +x /usr/local/bin/docker-app-entrypoint
 
-COPY docker/app/install-composer.sh /usr/local/bin/docker-app-install-composer
-RUN chmod +x /usr/local/bin/docker-app-install-composer
-
-RUN set -xe \
-	&& docker-app-install-composer \
-	&& mv composer.phar /usr/local/bin/composer
+WORKDIR /srv/app
+ENTRYPOINT ["docker-app-entrypoint"]
+CMD ["php-fpm"]
 
 # https://getcomposer.org/doc/03-cli.md#composer-allow-superuser
 ENV COMPOSER_ALLOW_SUPERUSER 1
@@ -40,9 +36,6 @@ ENV COMPOSER_ALLOW_SUPERUSER 1
 # Use prestissimo to speed up builds
 RUN composer global require "hirak/prestissimo:^0.3" --prefer-dist --no-progress --no-suggest --optimize-autoloader --classmap-authoritative  --no-interaction
 
-COPY docker/app/docker-entrypoint.sh /usr/local/bin/docker-app-entrypoint
-RUN chmod +x /usr/local/bin/docker-app-entrypoint
-
 # Allow to use development versions of Symfony
 ARG STABILITY=stable
 ENV STABILITY ${STABILITY}
@@ -50,12 +43,12 @@ ENV STABILITY ${STABILITY}
 # Download the Symfony skeleton and leverage Docker cache layers
 RUN composer create-project "symfony/skeleton" . --stability=$STABILITY --prefer-dist --no-dev --no-progress --no-scripts --no-plugins --no-interaction
 
+###> recipes ###
+###< recipes ###
+
 COPY . .
 
 RUN mkdir -p var/cache var/logs var/sessions \
     && composer install --prefer-dist --no-dev --no-progress --no-suggest --classmap-authoritative --no-interaction \
 	&& composer clear-cache \
-	&& chown -R www-data var # Permissions hack because setfacl does not work on Mac and Windows
-
-ENTRYPOINT ["docker-app-entrypoint"]
-CMD ["php-fpm"]
+	&& chown -R www-data var