The 'Hello World' of Dockerfiles for Kubernetes

29 Jun 2024 // programming

At work, I've been setting up custom Docker containers on a Kubernetes pipeline.

Since there was so much to get right, I first wanted to deploy a simple Docker container to see if the pipeline was working.

So I went around looking for simple examples - Python, Node, etc. - and eventually I found a little Nginx Dockerfile that serves a "Hello World" from an index.html on port 80:

FROM nginx:alpine
COPY index.html /usr/share/nginx/html

This was pretty good but it had one issue: as nginx runs in the background, Kubernetes will just stop the container after launching.

So to fix that, we'll have to run nginx in the foreground:

nginx -g 'daemon off;'

And by inlining the index.html, this results in a very convenient single file Dockerfile:

FROM nginx:alpine
RUN echo "<body>Hello World!</body>" > /usr/share/nginx/html/index.html
CMD ["nginx", "-g", "daemon off;"]

Finally, to test the Dockerfile locally, here's a nifty run.sh:

name="$(docker image ls |  grep web-server-test | awk '{print $1;}')"
if [ $name ]; then
    echo "Deleting container $name"
    docker image rm $name
fi
docker build -f Dockerfile . -t web-server-test
docker run  -p 80:80 web-server-test