Docker Image for Qt Development and Continuous Integration on x64 and arm64

Intro

It happens from time to time that I would benefit from having a simple Docker image with all the deps needed to build and run Qt apps on specific Qt versions. For instance, I may need to build some binary on Mac OS for Linux or I may need to have an image for some continuous integration system.

Problem

I had a look around and there are quite a few projects: some do not provide an arm build, some rely on the Qt official installer, that is a bit tricky to automate and tends to change often, some rely on distro-provided packages, that do not provide every version etc… I’d prefer to have a solid build procedure to build images for any Qt version I want. Also, my CI system runs on arm64, so I’d need a multiarch image, and therefore two different Qt builds. I thought it could be simpler to just build Qt on-the-fly in a Dockerfile but… turned out it is not exactly simple.

Solution

At first I created a Dockerfile to:

1. install all the needed deps on Ubuntu focal;
2. download Qt sources;
3. configure;
4. build;
5. install;
6. cleanup.

This proved to be a simple solution, but building Qt for arm on qemu or building on arm took way too much. So I though of a different solution. I created two images:

• carlonluca/qt-builder is an image with the proper tools to build Qt for x64 and cross-build Qt for arm64;
• carlonluca/qt-dev is an image with the proper tools to build and run Qt apps.

With the first image Qt can be built and cross-built in a few hours for both x64 and arm64, directly on x64. The builds are then injected into a second multiarch image. This is way faster than building on qemu.

Only one problem left: in Qt 5, crossbuilding Qt results in some Qt tools like qmake to be built for the host arch, which is unacceptable in this case. So, in the second image, a build of the only qtbase module is also needed to build arm64 binaries. Qt 6 works differently instead.

Result

The code to build Qt and all the images are available at: https://github.com/carlonluca/docker-qt.

The image to build Qt is available at: https://hub.docker.com/repository/docker/carlonluca/qt-builder.

The image to use for app development is available at: https://hub.docker.com/repository/docker/carlonluca/qt-dev.

Continuous Integration on GitLab with Qt

An example of usage of the dev image is running continuous integration and unit tests on your code on Jenkins or GitLab. For example, I can now run my unit tests in my GitLab instance running on Raspberry Pi 4 with the following code (taken from my project https://github.com/carlonluca/lqobjectserializer):

variables:

GIT_SUBMODULE_STRATEGY: recursive

stages:
  - test_qt5
  - test_qt6

Test_qt5:
  stage: test_qt5
  image:
    name: "carlonluca/qt-dev:5.15.2"
    entrypoint: [""]
  script:
    - cd LQObjectSerializerTest
    - mkdir build
    - cd build
    - cmake ../qt5
    - make
    - ./LQObjectSerializerTest
    - ./LGithubTestCase

Test_qt6:
  stage: test_qt6
  image:
    name: "carlonluca/qt-dev:6.1.2"
    entrypoint: [""]
  script:
    - cd LQObjectSerializerTest
    - mkdir build
    - cd build
    - cmake ../qt6
    - make
    - ./LQObjectSerializerTest
    - ./LGithubTestCase

These images are still experimental though.

Have fun 😉

Bye!