How to use alpine to reduce docker image size? - Stack Overflow

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I am trying to minimize of size of my Docker image as small as possible, the Dockerfile looks like this:

ARG DISTRO=fedora
ARG FEDORA_VERSION=36

#FROM ${DISTRO}:${FEDORA_VERSION} AS dev
FROM ${DISTRO}:${FEDORA_VERSION} AS dev


#Toolchain
RUN dnf -y install \
        gcc gcc-c++ \
        pkgconfig \
        cmake make \
        autoconf automake autogen libtool \
        flex bison \
        git rpm-build

#Dependencies
RUN dnf -y install \
        openssl-devel \
        #libuuid-devel \
        libcurl-devel \
        jansson-devel \
        spdlog-devel \
        fmt-devel \
        libconfig-devel \
        libusb-devel \
        lua-devel \
        libnice-devel \
        libwebsockets-devel

# Add local and 64-bit locations to linker paths
RUN echo /usr/local/lib   >> /etc/ld.so.conf && \
        echo /usr/local/lib64 >> /etc/ld.so.conf

ADD packaging/deps.sh / 
RUN bash deps.sh

EXPOSE 80
EXPOSE 443

ENV LC_ALL C.UTF-8
ENV LANG C.UTF-8

FROM dev AS builder

ARG FLAGS

# Disable all default features
RUN FLAGS+=" -DWITH_DEFAULTS=OFF" && \
# Enable the villas-* binaries from ./src again
    FLAGS+=" -DWITH_SRC=ON" && \
# Enable the villas-* tools from ./tools again
    FLAGS+=" -DWITH_TOOLS=ON" && \
# Enable libconfig configuration syntax
    FLAGS+=" -DWITH_CONFIG=ON" && \
# Enable the nodes
    FLAGS+=" -DWITH_NODE_TEST_RTT=ON" && \
    FLAGS+=" -DWITH_NODE_WEBRTC=ON" && \
    FLAGS+=" -DWITH_NODE_SIGNAL=ON" && \
# Enable hooks, in&out support
    FLAGS+=" -DWITH_IN=ON" && \
    FLAGS+=" -DWITH_HOOKS=ON" && \
    FLAGS+=" -DWITH_OUT=ON"


COPY . /villas/

WORKDIR /villas/build
RUN cmake ${FLAGS} -S .. && \
    make -j$(nproc) install && \
    ldconfig


ENTRYPOINT ["villas"]

So far, i tried to reduce the number of dependencies and the layers. But i found out that the dependencies can not be pruned anymore, deleting any one of them will lead to failure when building the Dockerfile. And by reducing the layers did not help much.

So i tried to use 'Alpine Linux base image' to reduce the image size, and i tried it by adding 'FROM alpine:latest' before 'COPY . /villas/'. But it didn't work, i could not build the Dockerfile with it. So what is the right way in my case to reduce the size of image using 'Alpine Linux base image'?

I am trying to minimize of size of my Docker image as small as possible, the Dockerfile looks like this:

ARG DISTRO=fedora
ARG FEDORA_VERSION=36

#FROM ${DISTRO}:${FEDORA_VERSION} AS dev
FROM ${DISTRO}:${FEDORA_VERSION} AS dev


#Toolchain
RUN dnf -y install \
        gcc gcc-c++ \
        pkgconfig \
        cmake make \
        autoconf automake autogen libtool \
        flex bison \
        git rpm-build

#Dependencies
RUN dnf -y install \
        openssl-devel \
        #libuuid-devel \
        libcurl-devel \
        jansson-devel \
        spdlog-devel \
        fmt-devel \
        libconfig-devel \
        libusb-devel \
        lua-devel \
        libnice-devel \
        libwebsockets-devel

# Add local and 64-bit locations to linker paths
RUN echo /usr/local/lib   >> /etc/ld.so.conf && \
        echo /usr/local/lib64 >> /etc/ld.so.conf

ADD packaging/deps.sh / 
RUN bash deps.sh

EXPOSE 80
EXPOSE 443

ENV LC_ALL C.UTF-8
ENV LANG C.UTF-8

FROM dev AS builder

ARG FLAGS

# Disable all default features
RUN FLAGS+=" -DWITH_DEFAULTS=OFF" && \
# Enable the villas-* binaries from ./src again
    FLAGS+=" -DWITH_SRC=ON" && \
# Enable the villas-* tools from ./tools again
    FLAGS+=" -DWITH_TOOLS=ON" && \
# Enable libconfig configuration syntax
    FLAGS+=" -DWITH_CONFIG=ON" && \
# Enable the nodes
    FLAGS+=" -DWITH_NODE_TEST_RTT=ON" && \
    FLAGS+=" -DWITH_NODE_WEBRTC=ON" && \
    FLAGS+=" -DWITH_NODE_SIGNAL=ON" && \
# Enable hooks, in&out support
    FLAGS+=" -DWITH_IN=ON" && \
    FLAGS+=" -DWITH_HOOKS=ON" && \
    FLAGS+=" -DWITH_OUT=ON"


COPY . /villas/

WORKDIR /villas/build
RUN cmake ${FLAGS} -S .. && \
    make -j$(nproc) install && \
    ldconfig


ENTRYPOINT ["villas"]

So far, i tried to reduce the number of dependencies and the layers. But i found out that the dependencies can not be pruned anymore, deleting any one of them will lead to failure when building the Dockerfile. And by reducing the layers did not help much.

So i tried to use 'Alpine Linux base image' to reduce the image size, and i tried it by adding 'FROM alpine:latest' before 'COPY . /villas/'. But it didn't work, i could not build the Dockerfile with it. So what is the right way in my case to reduce the size of image using 'Alpine Linux base image'?

• docker
• alpine-linux

Share Improve this question Follow asked Jan 23 at 13:27 HUH987HUH987 1755 bronze badges 4

• It doesn't work because dnf is a package manager for Fedora, RHEL, CentOS, Rocky and other distors. It's not supported by Alpine. Alpine uses apk. You should clean up after the installation of packages or even avoid package managers at all in order to minimize the image size. – jabaa Commented Jan 23 at 14:02
• How to clean up after this installation of packages? – HUH987 Commented Jan 23 at 14:07
• There is no cleanup after apk. Use hadolint to check Dockerfiles. – KamilCuk Commented Jan 23 at 14:08
• This depends on the distro and package manager. Most package managers store unnecessary package meta data. dnf has dnf clean. Since Alpine is designed for minimal image sizes, apk cleans up after itself. – jabaa Commented Jan 23 at 14:09

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2 Answers 2

Sorted by: Reset to default 1

The most important thing you can do with this setup is to introduce a multi-stage build. The image as you've shown it contains a complete C toolchain and development libraries, which are quite large. The size difference between a Fedora and Alpine image is miniscule compared to this (50-100 MB of base image, compared to 1 GB+ of toolchain and libraries).

The Dockerfile already starts with FROM image AS name syntax to declare a named stage. You need to add a third stage at the end:

FROM ${DISTRO}:${FEDORA_VERSION}

# Install non-development versions of C shared libraries that will
# be used at runtime.  See https://packages.fedoraproject.org/
# to find package names.
RUN dnf -y install \
      openssl-libs \
      libcurl \
      ...

# Copy the installed application into the final image.
COPY --from=builder /usr/local /usr/local
RUN ldconfig

# Set metadata for how to run the image.
# USER ...
# EXPOSE ...
CMD ["villas"]

This image will still be based on Fedora and not Alpine, but it will be substantially smaller than the image you're using now.

---

In principle it's possible to change that last FROM line to FROM alpine. You'll need to use Alpine's apk package manager instead of Fedora's dnf, and find dependencies on https://pkgs.alpinelinux.org/packages.

However, note that one of the things that makes Alpine-based images smaller is using an alternate C system library, musl libc instead of GNU libc. There are a number of very-low-level incompatibilities here. Many things will work with musl libc, but not all. If your application depends on a significant number of other shared libraries and also installs its own, I'd be worried about weird compatibility problems.

The easiest answer here often is to rewrite the entire build system to be Alpine- and not Fedora-based. A complete rewrite is beyond the scope of this answer. It's possible your application will run into build-time or link-time problems as well, but these should give clear pointers into your source code.

The multi-stage build approach will save you a huge amount of space in the final image. You may decide that saving a relatively small amount of space by switching base distributions isn't worth the effort of completely rebuilding and debugging the Dockerfile.

what is the right way in my case to reduce the size of image using 'Alpine Linux base image'?

The right way is rewritting the Dockerfile to support alpine linux, which is called "porting". Most significant change, as with any Linux distribution, is different package manager - apk in Alpine linux.

Additionally, not everything supports musl C standard library that is used in alpine linux, so the software has to be additionally rewritten or patched to work with musl C standard library.

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