Docker custom .deb file location - docker

Question

I had to compile a custom kernel to get Ubuntu to run on my laptop and now I'm trying to run docker containers on it.
It generated packages I installed:
linux-headers-5.15.30-25.25custom_5.15.30-25.25custom-1_amd64.deb
linux-image-5.15.30-25.25custom-dbg_5.15.30-25.25custom-1_amd64.deb
linux-image-5.15.30-25.25custom_5.15.30-25.25custom-1_amd64.deb
Now when I try to create docker images I get the following error:
...
Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package linux-headers-5.15.30-25.25custom
E: Couldn't find any package by glob 'linux-headers-5.15.30-25.25custom'
E: Couldn't find any package by regex 'linux-headers-5.15.30-25.25custom'
The Dockerfile just pulls an nvidia image and adds some other packages required
FROM nvidia/cuda:11.4.2-devel-ubuntu18.04
ARG COMPILE_GRAPHICS=OFF
ARG DEBIAN_FRONTEND=noninteractive
USER root
RUN \
set -ex && \
apt-key update && \
apt-get update && \
apt-get install -y -q \
build-essential \
software-properties-common \
openssl \
curl && \
rm -rf /var/lib/apt/lists/* && \
rm -rf /var/cache/apt/archives/ && \
rm -rf /usr/share/doc/ && \
rm -rf /usr/share/man/
...
It is installed on the host PC
~$ sudo dpkg -l | grep linux-headers-5.15.30-25.2
ii linux-headers-5.15.30-25.25custom 5.15.30-25.25custom-1 amd64 Linux kernel headers for 5.15.30-25.25custom on amd64
There's no problem on other machines using the upstream Ubuntu kernel packages.
So guess docker needs the actual package. How can I add a custom location to fetch the packages?
Thanks

Answer 1

I get the feeling you are mixing up what is outside and inside of a container.
Outside - on your host operating system you had to compile a custom kernel to get Linux running. So far so good.
Now you are trying to build a docker container. So the next steps are happening inside the container. Docker is lightweight virtualization therefore the container runs on the same kernel as the host. Since some package dependency is on the kernel's headers, and apt is trying to install the Debian package for them but cannot find them. Seems obvious as you are running a custom kernel and the package is in none well-known repository.
To get out of the situation:
check whether the headers for your kernel are available as .deb
make that .deb available inside the container. This may happen by placing them into the Docker build context.
ensure your Dockerfile installs the .deb before installing whatever needs that .deb. This will prevent it is searched in online repositories.