Docker on the Raspberry PI

This post intends to illustrate how Docker can work around the "But it works on my machine!.." syndrome.

Let's say you have a nodejs project you want to share with others.
The application reads GPS data through a Serial port, and feeds a WebSocket server.
The data can then be visualized through a Web interface.

To enable everything, you need to:

1. Have a Raspberry PI
2. Flash its SD card and connect it to a network
3. Install build tools
4. Install git
5. Install NodeJS and npm
6. Clone the right git repository
7. Install all the required node modules
8. Drill down into the right directory
9. Start the node server with the right script
10. Access the Raspberry PI from another machine on the same network, and reach the right HTML page.

This is certainly not difficult, but there are many ways to do several mistakes at each step of the process!

Docker can take care of the steps 3 to 9. It will build the image, and then run it.
The image can also be pushed to a repository, so users would not have to build it.
Just to run it after downloading it.

The only pre-requisite would be to have installed Docker on the machine (the Raspberry PI here), as explained here.
Create a Dockerfile like this (available here):

 FROM resin/raspberrypi3-debian:latest

 LABEL maintainer="Olivier LeDiouris <olivier@lediouris.net>"

 RUN echo "alias ll='ls -lisah'" >> $HOME/.bashrc

 RUN apt-get update
 RUN apt-get install sysvbanner
 RUN apt-get install -y curl git build-essential
 RUN curl -sL https://deb.nodesource.com/setup_9.x | bash -
 RUN apt-get install -y nodejs
 RUN echo "banner Node-PI" >> $HOME/.bashrc
 RUN echo "git --version" >> $HOME/.bashrc
 RUN echo "echo -n 'node:' && node -v" >> $HOME/.bashrc
 RUN echo "echo -n 'npm:' && npm -v" >> $HOME/.bashrc

 RUN mkdir /workdir
 WORKDIR /workdir
 RUN git clone https://github.com/OlivierLD/node.pi.git
 WORKDIR /workdir/node.pi
 RUN npm install

 EXPOSE 9876
 CMD ["npm", "start"]

In this case, the full Docker image creation (named oliv-nodepi below) comes down to 1 line (the one in bold red):

 $ docker build -t oliv-nodepi .
Sending build context to Docker daemon  752.6kB
Step 1/20 : FROM resin/raspberrypi3-debian:latest
 ---> c542b8f7a388
Step 2/20 : MAINTAINER Olivier LeDiouris 
 ---> Using cache
 ---> b2ff0d7c489f
Step 3/20 : ADD nodepi.banner.sh /
 ---> 535733298dd1
Step 4/20 : RUN echo "alias ll='ls -lisah'" >> $HOME/.bashrc
 ---> Running in 09baf7261a55
Removing intermediate container 09baf7261a55
 ---> 71e1e4c95663
Step 5/20 : RUN apt-get update
 ---> Running in 5d817a941a14
Get:1 http://security.debian.org jessie/updates InRelease [94.4 kB]
Get:2 http://archive.raspbian.org jessie InRelease [14.9 kB]
Get:3 http://archive.raspberrypi.org jessie InRelease [22.9 kB]

...

npm notice created a lockfile as package-lock.json. You should commit this file.
added 166 packages in 81.166s
Removing intermediate container 13986530db28
 ---> 051eb94b8a3c
Step 19/20 : EXPOSE 9876
 ---> Running in 67b587845fe0
Removing intermediate container 67b587845fe0
 ---> 46973b7ba9ac
Step 20/20 : CMD ["npm", "start"]
 ---> Running in 153bf2ea02ad
Removing intermediate container 153bf2ea02ad
 ---> 6bf3d76d38ae
Successfully built 6bf3d76d38ae
Successfully tagged oliv-nodepi:latest
ed9a7d9042dddd3939b1788cf0e89d16f5273192a6456266507f072f90ce91bc
 $

Once the step above is completed, plug in your GPS, and run

 $ docker run -p 9876:9876 -t -i --privileged -v /dev/ttyUSB0:/dev/ttyUSB0 -d oliv-nodepi:latest

Then from a machine seeing the Raspberry PI on its network (it can be the Raspberry PI itself), reach http://raspi:9876/data/demos/gps.demo.wc.html in a browser.

This shows you the position the GPS has computed, and the satellites in sight.
You can also login to the image:

 $ docker run -it oliv-nodepi:latest /bin/bash

 #     #                                 ######    ###
 ##    #   ####   #####   ######         #     #    #
 # #   #  #    #  #    #  #              #     #    #
 #  #  #  #    #  #    #  #####   #####  ######     #
 #   # #  #    #  #    #  #              #          #
 #    ##  #    #  #    #  #              #          #
 #     #   ####   #####   ######         #         ###

 git version 2.1.4
 node:v9.11.1
 npm:5.6.0
 root@b9679d0d65a7:/workdir/node.pi#

... and do whatever you like.
The build operation needs to be done once.
There is no need to do it again as long as no change in the image is required.

Quick comment

So, with Docker, you do not deliver a software, you actually deliver an image (a virtual machine), on which a software is running.
This is indeed redefining the concept of portability that made Java and other JVM-aware languages so successful.
This may very well explain the rise of languages like Golang (aka Go).
It runs on my machine? Well, here is my machine! You can download and run it. Enjoy!