Make default node-env use alpine. List envs in documentation. (#354)

closes #319 

* Make default node-env use alpine, and support separate debian env. List envs in documentation.

* Copy ONBUILD base image commands into node Dockerfiles

* Copy more commands from onbuild image

* Tidy dockerfiles

environments/nodejs/Dockerfile

@@ -1,7 +1,18 @@
 # A docker image for the func container.
 
-FROM node:8-onbuild
+# default variant is the official alpine node image (much smaller than the standard image)
+FROM node:8-alpine
 
-ADD server.js /usr/src/app/server.js
+ARG NODE_ENV
+ENV NODE_ENV $NODE_ENV
 
-EXPOSE 8888
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+
+COPY package.json /usr/src/app/
+RUN npm install && npm cache clean --force
+COPY server.js /usr/src/app/server.js
+
+CMD [ "npm", "start" ]
+
+EXPOSE 8888

environments/nodejs/Dockerfile-debian

@@ -0,0 +1,18 @@
+# A docker image for the func container.
+
+# debian variant is the official standard node image (larger than the alpine image)
+FROM node:8
+
+ARG NODE_ENV
+ENV NODE_ENV $NODE_ENV
+
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+
+COPY package.json /usr/src/app/
+RUN npm install && npm cache clean --force
+COPY server.js /usr/src/app/server.js
+
+CMD [ "npm", "start" ]
+
+EXPOSE 8888