We will install a current Debian release to a build environment which will spawn in an isolated light-weight namespace container.

mount /var/lib/machines/build
debootstrap --arch amd64 bookworm /var/lib/machines/build/ http://ftp.de.debian.org/debian/

Create a start script to spawn the container.

cat << EOF > ~/bin/c-buildstart.sh
#!/bin/sh
mount /var/lib/machines/build
systemd-nspawn -D /var/lib/machines/build
EOF

Copy custom shell configuration to the container.

cp ~/.bashrc /var/lib/machines/build/root/
umount /var/lib/machines/build/

Namespace container

Prepare the container which will be used as our build environment.

c-buildstart.sh
apt purge nano isc-dhcp-client isc-dhcp-common; \
apt install vim locales; \
dpkg-reconfigure locales

We will be using the following locales.

Generating locales (this might take a while)...                                                                                                                                                       
  de_DE.UTF-8... done
  en_GB.UTF-8... done
  en_US.UTF-8... done
Generation complete.

Create a very basic vim configuration.

cat << EOF > ~/.vimrc
syntax on
colorscheme default
set ruler
EOF

We will make sure the current release gets preferred over other available sources.

cat << EOF > /etc/apt/preferences.d/99-debian
package: *
Pin: release o=Debian,n=bookworm
Pin-Priority: 1001
EOF

Add the binary and source repositories.

cat << EOF > /etc/apt/sources.list
deb http://ftp.de.debian.org/debian/ bookworm main contrib non-free non-free-firmware
deb http://ftp.de.debian.org/debian/ bookworm-updates main contrib non-free non-free-firmware
deb https://deb.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
EOF

cat << EOF > /etc/apt/sources.list.d/sources.list
deb-src http://ftp.de.debian.org/debian/ testing main contrib non-free
deb-src http://ftp.de.debian.org/debian/ unstable main contrib non-free
deb-src http://ftp.de.debian.org/debian/ experimental main contrib non-free
EOF

Finalize our build environment.

apt install ca-certificates && apt update && apt upgrade

Build packages

apt install debian-keyring dpkg-dev fakeroot debhelper
chown _apt /usr/local/src

cd /usr/local/src
apt source <package>
cd <package-dir>
build-package

Skip tests

If some tests fail during our build, we may want to disable these extra checks.

DEB_BUILD_OPTIONS=nocheck dpkg-buildpackage

Add packages to repository

We want to add our packages to our custom repository.

cp /var/lib/machines/build/usr/local/src/*.deb /home/builds/<package>
c-buildstop.sh
find /home/builds/<package> -name '*1.2.3-4*' | xargs reprepro includedeb bookworm

reprepro listmatched bookworm 'postfix*'
reprepro listfilter bookworm 'Version (% *3.8.3* )'
reprepro --list-format '${package}\n' listfilter bookworm 'Version (% *3.8.3* )'