Update Dockerfile to make image smaller

- Added multistaged build
 - Moved production depedencies to final stage
 - Added more verbose output during build

Dockerfile

@@ -1,8 +1,12 @@
-FROM node:10.14-alpine
+# Mutistaged Node.js Build
+FROM node:10-alpine as builder
 
-RUN apk add --update pwgen netcat-openbsd python make gcc git g++ bash imagemagick
+# Install system dependencies
+RUN set -ex; \
+    apk add --update --no-cache \
+    make gcc g++ git
 
-# First install dependencies
+# Copy package.json dependencies
 COPY server/package.json /app/server/package.json
 COPY server/package-lock.json /app/server/package-lock.json
 COPY client/package.json /app/client/package.json
@@ -14,13 +18,29 @@ COPY zone-mta/package-lock.json /app/zone-mta/package-lock.json
 
 WORKDIR /app/
 
-RUN for idx in client shared server zone-mta; do (cd $idx && npm install); done
+# Install dependencies in each directory
+RUN set -ex; \
+   for idx in client shared server zone-mta; do (cd $idx && npm install); done
 
 # Later, copy the app files. That improves development speed as buiding the Docker image will not have
 # to download and install all the NPM dependencies every time there's a change in the source code
 COPY . /app
 
-RUN cd client && npm run build
+RUN set -ex; \
+   cd client && \
+   npm run build
+
+# Final Image
+FROM node:10-alpine
+
+WORKDIR /app/
+
+# Install system dependencies
+RUN set -ex; \
+    apk add --update --no-cache \
+    pwgen netcat-openbsd bash imagemagick
+
+COPY --from=builder /app/ /app/
 
 EXPOSE 3000 3003 3004
 ENTRYPOINT ["bash", "/app/docker-entrypoint.sh"]