Rework docker images build

.github/workflows/container-image.yml

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+name: Container Image
+
+on:
+  push:
+    branches:
+      - master
+  pull_request: {}
+  release:
+    types:
+      - published
+
+concurrency:
+  group: container-image-${{ github.event_name == 'push' && github.sha || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  container-image:
+    # Required by the base Container Image Action [^1].
+    # [^1]: https://github.com/Icinga/github-actions/blob/main/.github/workflows/container-image.yml#L54-L58
+    permissions:
+      contents: read
+      packages: write
+      attestations: write
+      id-token: write
+
+    name: Container Image
+    uses: icinga/github-actions/.github/workflows/container-image.yml@main
+    with:
+      documentation_url: https://icinga.com/docs/icinga2
+    secrets:
+      dockerhub_username: ${{ secrets.DOCKERHUB_USERNAME }}
+      dockerhub_token: ${{ secrets.DOCKERHUB_TOKEN }}

Containerfile

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+# Icinga 2 Docker image | (c) 2025 Icinga GmbH | GPLv2+
+
+FROM debian:trixie-slim AS build-base
+
+# Install all the necessary build dependencies for building Icinga 2 and the plugins.
+#
+# This stage includes the build dependencies for the plugins as well, so that they can share the same base
+# image, since Docker builds common stages only once [^1] even if they are used in multiple build stages.
+# This eliminates the need to have a separate base image for the plugins, that basically has kind of the
+# same dependencies as the Icinga 2 build stage (ok, not exactly the same, but some of them are shared).
+#
+# [^1]: https://docs.docker.com/build/building/best-practices/#create-reusable-stages
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install -y --no-install-recommends --no-install-suggests \
+        autoconf \
+        automake \
+        bison \
+        ccache \
+        cmake \
+        flex \
+        g++ \
+        git \
+        libboost1.83-dev \
+        libboost-context1.83-dev \
+        libboost-coroutine1.83-dev \
+        libboost-date-time1.83-dev \
+        libboost-filesystem1.83-dev \
+        libboost-iostreams1.83-dev \
+        libboost-program-options1.83-dev \
+        libboost-regex1.83-dev \
+        libboost-system1.83-dev \
+        libboost-thread1.83-dev \
+        libboost-test1.83-dev \
+        libedit-dev \
+        libmariadb-dev \
+        libpq-dev \
+        libssl-dev \
+        libsystemd-dev \
+        make && \
+    rm -rf /var/lib/apt/lists/*
+
+# Set the default working directory for subsequent commands of the next stages.
+WORKDIR /icinga2-build
+
+FROM build-base AS build-plugins
+
+# Install all the plugins that are not included in the monitoring-plugins package.
+ADD https://github.com/lausser/check_mssql_health.git#747af4c3c261790341da164b58d84db9c7fa5480 /check_mssql_health
+ADD https://github.com/lausser/check_nwc_health.git#a5295475c9bbd6df9fe7432347f7c5aba16b49df /check_nwc_health
+ADD https://github.com/bucardo/check_postgres.git#58de936fdfe4073413340cbd9061aa69099f1680 /check_postgres
+ADD https://github.com/matteocorti/check_ssl_cert.git#341b5813108fb2367ada81e866da989ea4fb29e7 /check_ssl_cert
+
+WORKDIR /check_mssql_health
+RUN mkdir bin && \
+    autoconf && \
+    autoreconf && \
+    ./configure "--build=$(uname -m)-unknown-linux-gnu" --libexecdir=/usr/lib/nagios/plugins && \
+    make && \
+    make install DESTDIR="$(pwd)/bin"
+
+WORKDIR /check_nwc_health
+RUN mkdir bin && \
+    autoreconf && \
+    ./configure "--build=$(uname -m)-unknown-linux-gnu" --libexecdir=/usr/lib/nagios/plugins && \
+    make && \
+    make install DESTDIR="$(pwd)/bin"
+
+WORKDIR /check_postgres
+RUN mkdir bin && \
+    perl Makefile.PL INSTALLSITESCRIPT=/usr/lib/nagios/plugins && \
+    make && \
+    make install DESTDIR="$(pwd)/bin" && \
+    # This is necessary because of this build error: cannot copy to non-directory: /var/lib/docker/.../merged/usr/local/man
+    rm -rf bin/usr/local/man
+
+FROM build-base AS build-icinga2
+
+# To access the automated build arguments in the Dockerfile originated from the Docker BuildKit [^1],
+# we need to declare them here as build arguments. This is necessary because we want to use unique IDs
+# for the mount cache below for each platform to avoid conflicts between multi arch builds. Otherwise,
+# the build targets will invalidate the cache one another, leading to strange build errors.
+#
+# [^1]: https://docs.docker.com/reference/dockerfile/#automatic-platform-args-in-the-global-scope
+ARG TARGETPLATFORM
+
+# Icinga 2 build arguments.
+#
+# These arguments are used to configure the build of Icinga 2 and can be overridden
+# by the user when building the image. All of them have a default value suitable for our official image.
+ARG CMAKE_BUILD_TYPE=ReleaseWithDebInfo
+ARG ICINGA2_UNITY_BUILD=ON
+ARG ICINGA2_BUILD_TESTING=ON
+
+# The number of jobs to run in parallel when building Icinga 2.
+# By default, it is set to the number of available CPU cores on the build machine.
+ARG MAKE_JOBS=auto
+
+# Create the directory where the final Icinga 2 files will be installed.
+#
+# This directory will be used as the destination for the `make install` command below and will be
+# copied to the final image. Other than that, this directory will not be used for anything else.
+RUN mkdir /icinga2-install
+
+# Mount the source code as a bind mount instead of copying it, so that we can use the cache effectively.
+# Additionally, add the ccache and CMake build directories as cache mounts to speed up rebuilds.
+RUN --mount=type=bind,source=.,target=/icinga2,readonly \
+    --mount=type=cache,id=ccache-${TARGETPLATFORM},target=/root/.ccache \
+    --mount=type=cache,id=icinga2-build-${TARGETPLATFORM},target=/icinga2-build \
+    PATH="/usr/lib/ccache:$PATH" \
+    cmake -S /icinga2 -B /icinga2-build \
+        -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} \
+        # Podman supports forwarding notifications from containers to systemd, so build Icinga 2 with systemd support.
+        -DUSE_SYSTEMD=ON \
+        -DBUILD_TESTING=${ICINGA2_BUILD_TESTING} \
+        -DICINGA2_UNITY_BUILD=${ICINGA2_UNITY_BUILD} \
+        # The command group name below is required for the prepare-dirs script to work, as it expects
+        # the command group name, which by default is `icingacmd` to exist on the system. Since we
+        # don't create the `icingacmd` command group in this image, we need to override it with icinga.
+        -DICINGA2_COMMAND_GROUP=icinga \
+        -DCMAKE_INSTALL_PREFIX=/usr \
+        -DCMAKE_INSTALL_SYSCONFDIR=/data/etc \
+        -DCMAKE_INSTALL_LOCALSTATEDIR=/data/var \
+        -DICINGA2_SYSCONFIGFILE=/etc/sysconfig/icinga2 \
+        -DICINGA2_RUNDIR=/run \
+        -DICINGA2_WITH_COMPAT=OFF \
+        -DICINGA2_WITH_LIVESTATUS=OFF && \
+    make -j$([ "$MAKE_JOBS" = auto ] && nproc || echo "$MAKE_JOBS") && \
+    CTEST_OUTPUT_ON_FAILURE=1 make test && \
+    make install DESTDIR=/icinga2-install
+
+RUN rm -rf /icinga2-install/etc/icinga2/features-enabled/mainlog.conf \
+        /icinga2-install/usr/share/doc/icinga2/markdown && \
+    strip -g /icinga2-install/usr/lib/*/icinga2/sbin/icinga2 && \
+    strip -g /icinga2-install/usr/lib/nagios/plugins/check_nscp_api
+
+# Prepare the final image with the necessary configuration files and runtime dependencies.
+FROM debian:trixie-slim AS icinga2
+
+# The real UID of the Icinga user to be used in the final image.
+ARG ICINGA_USER_ID=5665
+
+# Install the necessary runtime dependencies for the Icinga 2 binary and the monitoring-plugins.
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends --no-install-suggests \
+        bc \
+        ca-certificates \
+        curl \
+        dumb-init \
+        file \
+        libboost1.83-dev \
+        libboost-context1.83-dev \
+        libboost-coroutine1.83-dev \
+        libboost-date-time1.83-dev \
+        libboost-filesystem1.83-dev \
+        libboost-iostreams1.83-dev \
+        libboost-program-options1.83-dev \
+        libboost-regex1.83-dev \
+        libboost-system1.83-dev \
+        libboost-thread1.83-dev \
+        libboost-test1.83-dev \
+        libcap2-bin \
+        libedit2 \
+        libldap-common \
+        libmariadb3 \
+        libmoosex-role-timer-perl \
+        libpq5 \
+        libssl3 \
+        libsystemd0 \
+        mailutils \
+        monitoring-plugins \
+        msmtp \
+        msmtp-mta \
+        openssh-client \
+        openssl && \
+    # Official Debian images automatically run `apt-get clean` after every install, so we don't need to do it here.
+    rm -rf /var/lib/apt/lists/*
+
+# Create the icinga user and group with a specific UID as recommended by Docker best practices.
+# The user has a home directory at /var/lib/icinga2, and if configured, that directory will also
+# be used to store the ".msmtprc" file created by the entrypoint script.
+RUN adduser \
+    --system \
+    --group \
+    --home /var/lib/icinga2 \
+    --disabled-login \
+    --no-create-home \
+    --uid ${ICINGA_USER_ID} icinga
+
+COPY --from=build-plugins /check_mssql_health/bin/ /
+COPY --from=build-plugins /check_nwc_health/bin/ /
+COPY --from=build-plugins /check_postgres/bin/ /
+COPY --from=build-plugins /check_ssl_cert/check_ssl_cert /usr/lib/nagios/plugins/check_ssl_cert
+
+COPY --from=build-icinga2 /icinga2-install/ /
+
+# Create a corresponding symlink in the root filesystem for all Icinga 2 directories in /data.
+# This is necessary because we want to maintain the compatibility with containers built with the
+# legacy Dockerfile, which expects the Icinga 2 directories to be in the root directory.
+RUN for dir in /etc/icinga2 /var/cache/icinga2 /var/lib/icinga2 /var/log/icinga2 /var/spool/icinga2; do \
+    ln -vs "/data$dir" "$dir"; \
+done
+
+# The below prepare-dirs script will not fix any permissions issues for the actuall /var/lib/icinga2 or
+# /etc/icinga2 directories, so we need to set the correct ownership for the /data directory recursively.
+RUN chown -R icinga:icinga /data
+
+# Run the prepare-dirs script to create non-existing directories and set the correct permissions for them.
+# It's invoked in the same way as in the systemd unit file in a Debian package, so this will ensure that
+# all the necessary directories are created with the correct permissions and ownership.
+RUN /usr/lib/icinga2/prepare-dirs /etc/sysconfig/icinga2
+
+# Well, since the /data directory is intended to be used as a volume, we should also declare it as such.
+# This will allow users to mount their own directories or even specific files to the /data directory
+# without any issues. We've already filled the /data directory with the necessary configuration files,
+# so users can simply mount their own files or directories if they want to override the default ones and
+# they will be able to do so without any issues.
+VOLUME ["/data"]
+
+COPY --chmod=0755 tools/container/entrypoint.sh /usr/local/bin/entrypoint.sh
+ENTRYPOINT ["/usr/bin/dumb-init", "-c", "--", "/usr/local/bin/entrypoint.sh"]
+
+EXPOSE 5665
+USER icinga
+
+CMD ["icinga2", "daemon"]