Optional CUPS utils on custom image

[martkaczmarek]

Is your feature request related to a problem? Please describe.
I am interested in adding "Silent printing"/"Backend printing" functionality to my Docker install.
I stumbled upon the docs here: https://docs.frappe.io/erpnext/print-settings#3-network-printer-print-server
As a test, I took my running container and installed libcups2-dev and cups packages (still don't know if cups itself is needed). After running ./env/bin/pip install pycups and then bench restart, looks like a success - Frappe connects to CUPS:

(it's definitely connecting becauses the printer name was fetched from the CUPS service)

Obviously it's just a test setup since the packages will not be retained in the container this way.

My question is: could we add the required packages and commands to dockerfile as optional, dependant on some build arg (e.g. INCLUDE_CUPS)? Of course it wouldn't be a good idea to add it for everyone since these packages easily add like 600MB of data.

I am definitely not an expert in dockerfiles so can't offer much contribution myself, but I'm happy to test things.

Describe alternatives you've considered
A different approach is to not use built-in function at all, instead to build separate module for generating PDFs and sending it to a dedicated container managing print jobs. A bit more convoluted.

Keep in mind all of that requires further testing, I just wanted to stop at "I think it could work".

[jslocomotor]

You are on the right track when thinking about dockerfiles / containerfiles. Inside you could install all kind of linux programs to support your ERPNext instance. - Like CUPS.
What you can do is build on top of images generated by containerfiles of this repo or the official frappe/erpnext images. So you'll stay compliant to this repo while adding custom software manageably.

For example:
Create a Containerfile.cups

# Containerfile.cups
ARG BASE_IMAGE=frappe/erpnext:v16

FROM ${BASE_IMAGE}

USER root

RUN apt-get update \
  && apt-get install --no-install-recommends -y \
    build-essential \
    python3-dev \
    libcups2-dev \
    cups-client \
  && rm -rf /var/lib/apt/lists/*

USER frappe

RUN /home/frappe/frappe-bench/env/bin/pip install --no-cache-dir pycups

And then build it

docker build \
  -f Containerfile.cups \
  --build-arg BASE_IMAGE=registry.example.com/erpnext-custom:v16 \
  -t registry.example.com/erpnext-custom:v16-cups .

[martkaczmarek]

I definitely thought about this alternative - adding another 'layer' on top of custom Frappe container, and your example makes sense to me. But that adds even more complexity to building process - I'd have to build one custom container (I'm already doing that since I need custom modules) and then trigger another build from this exact version. It's a bit more jank than I'd like to see.
Alternative no. 2 - I can still just edit the original container file in my local building repo and add the lines.

But my bigger question is - would it be a worthy addition to this repoaitory, to add CUPS install commands based on optional build argument? Since the silent printing is a native function of Erpnext/Frappe, it would make sense to add an option to build a container with support for it.
Similar idea was suggested in #1859 regarding a build argument for including/not including Chromium in the image.

[jslocomotor]

What do you think? @DanielRadlAMR Should we implement more options to customize builds?

[Rocket-Quack]

This should be handled as an explicit opt-in in the custom image rather than by adding CUPS to the default, base, or build images.

With a opt-in build parameter like INSTALL_PYCUPS. Where the default is false but users can if they wish add this dependency.

This keeps the base and build image small and focused, while still allowing users to add the dependency through a self-built custom image when required.

We should also add detailed documentation for this approach. I expect more apps will need additional optional dependencies in the future, and without clear documentation we will quickly lose track of which dependencies are available, why they exist, and how users are expected to enable them.

[DanielRadlAMR]

i do agree with @Rocket-Quack

[martkaczmarek]

I have made some changes in my fork here:
https://github.com/martkaczmarek/frappe_docker/tree/feature-cups

for now I have added INSTALL_PYCUPS (defaults to false) argument in custom and production dockerfiles and apt-get install dependant on the value ; I don't know where exactly it should go in layered file.
I am also not sure where this command:
RUN /home/frappe/frappe-bench/env/bin/pip install --no-cache-dir pycups
should go (after all the bench initialisation?)
Also: should we use pip or pip3?

Please let me know if there are any important doc locations apart from 02-setup/02-build-setup.md that should get updated.

[DanielRadlAMR]

@martkaczmarek just open a PR — it makes it easier to review your changes 🙂
Even if it’s not ready yet, you can open it in draft mode.

[martkaczmarek]

Sure thing, here you go:
#1900