To enforce some rules, linters are used in this project. Linters can be run either during the development phase (by the developer) or the integration phase (by GitHub Actions). To integrate and enforce this process in the project lifecycle, we are using git hooks through pre-commit.

Using pre-commit hooks#

Pre-commit hook installation#

pre-commit is a Python package that needs to be installed. To achieve this, use the generic task to install all Python development dependencies.

# Install all development dependencies for the project
pip install --upgrade -r requirements-dev.txt
# It can also be installed directly
pip install pre-commit

Then the git hooks scripts configured for the project in .pre-commit-config.yaml need to be installed in the local git repository.

pre-commit install


Now, pre-commit (and so configured hooks) will run automatically on git commit on each changed file. However, it is also possible to trigger it against all files.


Hadolint pre-commit uses Docker to run, so docker should be running while running this command.

pre-commit run --all-files --hook-stage manual


We’re running pre-commit with --hook-stage manual, because works with changed files, which doesn’t work well for mypy. More information can be found in .pre-commit-config.yaml file

Image Lint#

To comply with Docker best practices, we are using the Hadolint tool to analyze each Dockerfile.

Ignoring Rules#

Sometimes it is necessary to ignore some rules. The following rules are ignored by default for all images in the .hadolint.yaml file.

  • DL3006: We use a specific policy to manage image tags.

    • The docker-stacks-foundation FROM clause is fixed but based on an argument (ARG).

    • Building downstream images from (FROM) the latest is done on purpose.

  • DL3008: System packages are always updated (apt-get) to the latest version.

  • DL3013: We always install the latest packages using pip

The preferred way to do it for other rules is to flag ignored ones in the Dockerfile.

It is also possible to ignore rules by using a special comment directly above the Dockerfile instruction you want to make an exception for. Ignore rule comments look like # hadolint ignore=DL3001,SC1081. For example:

FROM ubuntu

# hadolint ignore=DL3003,SC1035
RUN cd /tmp && echo "hello!"