Use multi-stage build, bump PHP, add etc/ directory

.dockerignore

@@ -0,0 +1,10 @@
+.dockerignore
+.gitignore
+.git
+.github
+.idea
+ansible
+build
+docs
+test
+vendor

Dockerfile

@@ -1,19 +1,19 @@
-FROM php:7.1-cli
-MAINTAINER Phing <info@phing.info>
+FROM composer:1.7 AS composer
 
-RUN apt-get update -qq -y && \
-    apt-get install -y --no-install-recommends git unzip && \
-    apt-get clean && \
-    rm -rf /var/lib/apt/lists/*
+ADD composer.* ./
+ADD classes/ classes
+RUN mkdir -p test/classes
 
-RUN curl -o composer.phar https://getcomposer.org/composer.phar
+RUN composer global require hirak/prestissimo --no-plugins --no-scripts
+RUN composer install --optimize-autoloader --prefer-dist --no-progress --no-interaction
+
+FROM php:7.2-cli-alpine AS phing
+MAINTAINER Phing <info@phing.info>
 
 ADD bin/phing* bin/
 ADD classes/ classes
-ADD composer.* ./
-
-RUN mkdir -p test/classes
+ADD etc/ etc
 
-RUN php composer.phar install -o && rm -rf ~/.composer
+COPY --from=composer /app/vendor/ ./vendor
 
 ENTRYPOINT ["phing"]