Running Spress in Docker

My last PHP update broke Spress, the static site generator I use for this blog. I decided to move my blog generation to a more stable and portable environment - a Docker container. I’ve documented what I did and what I learned with this blog post. This is my first attempt to do something with Docker, please excuse any bad practices.

You can find the finished Dockerfile at

Writing the Dockerfile

FROM php:alpine

As the base image I’m using the alpine variant of the official PHP Docker image to keep the storage space for the image as small as possible.

Since the docker container will only run on my local machine and is not intended to be deployed, I don’t bother setting up an extra user account. Everything will be run as root inside the container.

RUN curl -L -o /usr/local/bin/spress && \
chmod +x /usr/local/bin/spress

The installation of Spress is fairly simple: Download the Spress PHAR file and make it executable. The commands are chained with && instead of being individual RUN commands, because Docker internally creates a new image for every RUN command and I don’t want to clutter my hard disk with too many intermediary images.

WORKDIR /var/www
ENTRYPOINT [ "/usr/local/bin/spress" ]
CMD [ "site:build", "--watch", "--server" ]

WORKDIR is pretty self-explanatory: It’s the directory where all the following commands will be run.

ENTRYPOINT specifies the command that will always be run when the container is started.

CMD specifies what parameters will be passed to the command in ENTRYPOINT. They can be overwritten when starting the container. By default, a development server is started.

The Dockerfile is complete. Now a Docker image needs to be built with the command

docker build -t gbirke/spress .

The option -t gbirke/spress tags it for later submission to DockerHub. This will allow me to skip the build step when using it on other machines.

Runnning Spress

The docker run command takes a Docker image and runs it in a Docker container. The full command is

docker run -v $(pwd):/var/www -p 4000 --name serve_my_blog -t gbirke/spress

Let’s have a look at all the parameters

  • -v $(pwd):/var/www mounts the current directory as a volume inside the running container.
  • -p 4000 exposes port 4000 of the container to my host computer so I can reach the blog at http://localhost:4000/ from my browser.
  • --name serve_my_blog applies the name serve_my_blog to the image. If this parameter is missing, Docker will generate an arbitrary name like optimistic_payne or modest_agnesi.
  • -t assigns the running process a “pseudo-tty”. If I left this parameter out, I wouldn’t be able to detach myself from the docker image with Control-C. Using a pseudo-tty also means that Spress can use its colored output.

While the image is running, I can go to localhost:4000/ and browse my blog.

Stopping and restarting

If I want to detach myself from the running Spress web server, I can press Control-C. The image will still be running, but in a detached state.

With the command docker ps I can see a list of images, their names and their status. To attach my console back to the process to see its output I can use docker attach serve_my_blog (for full console access which is not needed here) or docker logs -f serve_my_blog for just reading the output.

A running image can be stopped the command docker stop serve_my_blog which will wait for 10 seconds an then stop the image. To stop immediately, I use docker stop -t 0 serve_my_blog.

When I’ve stopped a container, docker ps will not show it anymore. But it still exists, in a stopped state. I can see that with docker ps -a, which will show all containers. If I try to start the container again with docker run and the same name, I will get the error message the container name "/serve_my_blog" is already in use by container.

To restart the container with the same parameters, I could use the command docker restart serve_my_blog.

To start the image with different parameters, I’d first have to remove the stopped image. Removing all stopped images can be done with the command

docker rm $(docker ps -q -f "status=exited")

By adding the --rm parameter to the docker run command, the image will be removed automatically when the container stops.

By adding the -d parameter to the docker run command, the image will start in a detached state.

Usage without the web server

When I just want to build my blog with Spress, without having a web server or watching for file changes, I append the Spress command line options to the docker run command:

docker run -v $(pwd):/var/www --rm -t gbirke/spress site:build

Here is how I run it with my production configuration:

docker run -v $(pwd):/var/www --rm -t gbirke/spress site:build --env=prod


This was a fun little project. I’ve long dreaded looking into Docker, especially on macOS, my primary work OK. Now I’ve boarded the Docker hype train and will continue exploring the possibilities. I’ve already experimented with running MySQL in a Docker image for running tests for my “Remember me” library …