Why you might want to avoid building C++ applications w/ `vcpkg`
Dockerizing 🐳 a C++ application can be much more difficult than dockerizing a Node.js or Python application. And it is not the execution of the binary that is difficult (that is easy). It’s rather that compiling the source code requires a further stage in the Dockerfile, a so-called build stage, in which all build tools (gcc, cmake, etc.) and all dependencies (boost, zlib, etc.) must be installed and available.
To define these dependencies, one might be tempted to use vcpkg, a “C++ Library Manager for Windows, Linux, and MacOS” (https://github.com/microsoft/vcpkg), which is basically the equivalent of using npm+package.json in Node.js or pip+Pipfile in Python, right?
Unfortunately, it is not. This approach leads to several problems.
vcpkgfeels much clumsier than aPipfile, for example.vcpkgproves to be less robust than other package managers.- The build step with
vcpkgis much, much more time-consuming.
Where points 1 and 2 are also somewhat subjective, point 3 can be illustrated relatively easy.
For comparison:
git clone https://github.com/madietlx/dockerfiles.git
make -C dockerfiles/ubuntu-20-04-compile-cxx-with-vcpkg build
downloads a simple example in C++, including a Makefile and a Dockerfile (build and runtime environment in one), and compiles it. You will get more or less the following output:
docker build -t built-with-vcpkg:latest .
[+] Building 202.6s (16/16) FINISHED docker:desktop-linux
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 1.53kB 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:20.04 1.6s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 1.31kB 0.0s
=> [stage-1 1/4] FROM docker.io/library/ubuntu:20.04@sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae9 0.0s
=> => resolve docker.io/library/ubuntu:20.04@sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae91ee670e9 0.0s
=> => sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae91ee670e9c35d 1.13kB / 1.13kB 0.0s
=> => sha256:4aa61d4985265be6d872cc214016f2f91a77b1c925dab5ce502db2edc4a7e5af 424B / 424B 0.0s
=> => sha256:3048ba0785953b689215053519eb1c34853e2e3af512eed001be59fec1f32e42 2.31kB / 2.31kB 0.0s
=> [build 2/8] RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommend 16.2s
=> [stage-1 2/4] RUN groupadd -r otto && useradd -r -g otto otto 0.3s
=> [stage-1 3/4] WORKDIR /home/otto 0.0s
=> [build 3/8] WORKDIR /root 0.0s
=> [build 4/8] RUN wget --progress=dot:giga -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/d 26.4s
=> [build 5/8] RUN git clone https://github.com/microsoft/vcpkg && ./vcpkg/bootstrap-vcpkg.sh 65.2s
=> [build 6/8] RUN vcpkg/vcpkg install boost-iostreams boost-program-options 91.5s
=> [build 7/8] COPY src/ ./src 0.0s
=> [build 8/8] RUN cmake -DCMAKE_BUILD_TYPE=Release -S src -B src/build -DCMAKE_TOOLCHAIN_FILE=/root/vcpkg/scr 1.4s
=> [stage-1 4/4] COPY --from=build /root/src/build/ ./build 0.0s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:950072b6eb7802f8f30d3fdf09897376b3d6001d972a2471c935cd21ca56eef3 0.0s
=> => naming to docker.io/library/built-with-vcpkg:latest 0.0s
➡️ 202.6 seconds 🐌
For comparison (without vcpkg):
make -C dockerfiles/ubuntu-20-04-compile-cxx-without-vcpkg build
docker build -t built-without-vcpkg:latest .
[+] Building 21.7s (13/13) FINISHED docker:desktop-linux
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 546B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:20.04 1.3s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [build 1/5] FROM docker.io/library/ubuntu:20.04@sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae91e 0.0s
=> => resolve docker.io/library/ubuntu:20.04@sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae91ee670e9 0.0s
=> => sha256:80ef4a44043dec4490506e6cc4289eeda2d106a70148b74b5ae91ee670e9c35d 1.13kB / 1.13kB 0.0s
=> => sha256:4aa61d4985265be6d872cc214016f2f91a77b1c925dab5ce502db2edc4a7e5af 424B / 424B 0.0s
=> => sha256:3048ba0785953b689215053519eb1c34853e2e3af512eed001be59fec1f32e42 2.31kB / 2.31kB 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 1.26kB 0.0s
=> [build 2/5] RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommend 18.7s
=> [stage-1 2/4] RUN groupadd -r otto && useradd -r -g otto otto 0.3s
=> [stage-1 3/4] WORKDIR /home/otto 0.0s
=> [build 3/5] WORKDIR /root 0.0s
=> [build 4/5] COPY src/ ./src 0.0s
=> [build 5/5] RUN cmake -DCMAKE_BUILD_TYPE=Release -S src -B src/build && cmake --build src/build 1.5s
=> [stage-1 4/4] COPY --from=build /root/src/build/ ./build 0.1s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:2f0a4d8c966239cc521ff559847c9db3c98769f39e9dbe02aeeb6d9098a01118 0.0s
=> => naming to docker.io/library/built-without-vcpkg:latest 0.0s
➡️ 21.7 seconds 🚀
The massive difference is almost entirely due to the time it takes to bootstrap vcpkg and build the dependencies. The actual build step with cmake is then practically the same in both cases.
The bottom line is that not using vcpkg leads to faster builds as well as fewer (third-party) dependencies and is accomplished solely with the package management of the operating system (here: Ubuntu 20.04 (LTS) 🐧), which will be much more robust and less error-prone over the years.
P.S. This article was written in collaboration with a colleague of mine (@favph on GitHub), who was the first to point out the disadvantages of vcpkg to me that then led to this article. 🙏