Merge pull request #143 from misterjoshua/master

GNU Makefile so that all images can be built by typing, for example, make ruby/2.3.1

Author: subinataws

Makefile

@@ -0,0 +1,10 @@
+BUILDS=$(shell egrep -o 'ubuntu/[^ ]*' buildspec.yml | sed 's|^ubuntu/||')
+NAME=$(shell dirname $@)
+VERSION=$(shell basename $@)
+TAG=aws/codebuild/$(NAME):$(VERSION)
+
+all: $(BUILDS)
+
+$(BUILDS):
+	cd ubuntu/$(NAME)/$(VERSION) && \
+	docker build -t $(TAG) .

README.md

@@ -14,6 +14,10 @@ Steps to build Ruby 2.3.1 image
 * Run `cd ubuntu/ruby/2.3.1` to change the directory in your local workspace. This is the location of the Ruby 2.3.1 Dockerfile with Ubuntu 14.04 base.
 * Run `docker build -t aws/codebuild/ruby:2.3.1 .` to build Docker image locally
 
+Alternatively, you may use GNU make to build the above image:
+
+* Run `make ruby/2.3.1`. This will build the Docker image locally, as above, from a computer with GNU make.
+
 To poke around in the image interactively, build it and run:
 `docker run -it --entrypoint sh aws/codebuild/ruby:2.3.1 -c bash`