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Build a custom root filesystem

You can customise a Slicer VM in two ways:

  1. Via userdata on first boot (a bash script included via the config file)
  2. By extending an existing root filesystem with Docker and adding various COPY and RUN statements

When building within Docker, you must bear in mind that not all of the files shown to you will persist into the final image.

Additionally, if you're copying and pasting commands from installation guides, certain systemctl commands will need to be adapted.

If a guide gave you systemctl enable --now bind for a custom DNS server, you'd simply remove the --now flag. The meaning of --now is to instruct the build container to start a systemd service immediately - that's not possible or desirable during a build.

In short, if you are trying to extend a Slicer image, treat it as if it were a Docker container, and only run commands that you know work in a regular Dockerfile.

For anything that does not run or work within a Dockerfile, either use userdata to run the steps on first boot, or add a one-shot systemd unit file that will run your custom steps on first boot.

Build a custom image

First, refer to the image you want to customise - whether it's for aarch64 or x86_64.

Then create a Dockerfile with a FROM line specifying the base image you want to use. For example:

FROM ghcr.io/openfaasltd/slicer-systemd:5.10.240-x86_64-latest

If you wanted to install Nginx and have it start automatically, with a website you've created, you could add the following lines to your Dockerfile.

Nginx will run in systemd, we should not try to change the CMD instruction.

+RUN apt-get update && apt-get install -y nginx
+RUN systemctl enable nginx
+COPY ./my-website /var/www/html

Then build and publish the image to your own registry:

docker build -t docker.io/alexellis2/slicer-nginx:5.10.240-x86_64 .
docker push docker.io/alexellis2/slicer-nginx:5.10.240-x86_64

Then edit your Slicer YAML and replace the image: with docker.io/alexellis2/slicer-nginx:5.10.240-x86_64.

If you wanted Docker to be pre-installed into all your VMs, with the default user already set up for access, you could write:

+RUN curl -sLS https://get.docker.com | sh
+RUN usermod -aG docker ubuntu

If you want to run a local registry, without TLS authentication enabled, you can do so with the following within your YAML file:

config:
  insecure_registry: true

Then if you want to run a temporary Docker registry on another machine on your network:

docker run -d -p 5000:5000 --restart always \
  --name registry registry:3