use Semaphore Container Registry as a source for base image

Author: TomFern

.semaphore/docker-build.yml

@@ -32,7 +32,7 @@ blocks:
           # unique image tag.
           # For a list of available environment variables on Semaphore, see:
           # https://docs.semaphoreci.com/article/12-environment-variables
-          - docker build --cache-from "${DOCKER_USERNAME}"/semaphore-demo-ruby-kubernetes:latest -t "${DOCKER_USERNAME}"/semaphore-demo-ruby-kubernetes:$SEMAPHORE_WORKFLOW_ID .
+          - docker build --cache-from "${DOCKER_USERNAME}"/semaphore-demo-ruby-kubernetes:latest -t "${DOCKER_USERNAME}"/semaphore-demo-ruby-kubernetes:$SEMAPHORE_WORKFLOW_ID -f Dockerfile.ci .
           - docker images
 
           # Push a new image to Docker Hub container registry:

Dockerfile.ci

@@ -0,0 +1,17 @@
+#Pull image from Semaphore Container Registry
+FROM registry.semaphoreci.com/ruby:2.7
+
+RUN apt-get update -qq && apt-get install -y build-essential
+
+ENV APP_HOME /app
+RUN mkdir $APP_HOME
+WORKDIR $APP_HOME
+
+ADD Gemfile* $APP_HOME/
+RUN bundle install --without development test
+
+ADD . $APP_HOME
+
+EXPOSE 4567
+
+CMD ["bundle", "exec", "rackup", "--host", "0.0.0.0", "-p", "4567"]