Why learn Docker?
For me, learning about containers (and Docker in particular) is just part of my journey to keep up to date on the tools of modern software development. I don’t anticipate becoming a container expert or managing large Docker swarms (although you never know!), but having a decent understanding of the tools and technologies around containers fits into my process of using the best tools available for a given problem. I am fascinated to learn new ways to accomplish a task, not to mention that using containers for software development seems to be an idea that is sticking around. With that in mind, let the learning begin!
What exactly is Docker?
I won’t even pretend to give a better executive summary of containers and Docker than Docker themselves do, so I will spare you the attempt.
For a good overall summary of what Docker (and containers and images) is, I headed to the official Docker documentation, and was quickly up to speed on the overall benefits and high level idea behind containers.
Install Docker
While I primarily develop on Windows, for this project I wanted to utilize Linux as forced way to brush up on other skills that often do not get enough attention due to time constraints. I happened to have a Linux instance available from a previous project, so I fired it back up and connected to it via Windows Subsystem For Linux and SSH.
I installed the Docker CE (Community Edition)
My Linux install was Ubuntu based (Amazon Linux AMI), so make sure to use the proper instructions for your version of Linux.
Instructions I followed for Docker
Uninstall old versions of Docker
Don’t skip this step! I had a previous version of Docker installed (without knowing what I was doing), so I wanted make sure that was cleaned up first. If nothing was previously installed, nothing bad will happen.
Install and Confirm
Once I cleaned up my old install of Docker, I was able to successfully reinstall the current version of Docker CE, add my user to the docker group, and confirm the running status of Docker. Success!!
Create a Docker image
I ended up following the AWS introduction guide to Docker and created a ‘Hello World’ image that served a static web page from an instance of Apache. The tutorial was pretty straightforward, I only needed to tweak my AWS security group for the EC2 instance to allow for inbound connections on port 80 from my machine.
Dockerfile
FROM ubuntu:16.04
# Install dependencies
RUN apt-get update
RUN apt-get -y install apache2
# Install apache and write hello world message
RUN echo 'Hello World!' > /var/www/html/index.html
# Configure apache
RUN echo '. /etc/apache2/envvars' > /root/run_apache.sh
RUN echo 'mkdir -p /var/run/apache2' >> /root/run_apache.sh
RUN echo 'mkdir -p /var/lock/apache2' >> /root/run_apache.sh
RUN echo '/usr/sbin/apache2 -D FOREGROUND' >> /root/run_apache.sh
RUN chmod 755 /root/run_apache.sh
EXPOSE 80
CMD /root/run_apache.shBuild docker image
docker build -t hello-world .
Verify image
docker images --filter reference=hello-world
Run image
docker run -t -i -p 80:80 hello-worldI added the -t -i flags to allow Ctrl+C to be used to interrupt docker run. See this GitHub issue for a more complete discussion.
test!
Summary
I obviously still have lots to learn, but this first look at Docker was relatively painless and has already given me a whole set of ideas to try out and incorporate into my development processes.
Featured image by Tim Easley @ unsplash.com
