Gitlab CI/CD Example for Python-based Apps

CONTENTS

• DEPENDENCIES
• SETUP
• USAGE
• ISSUES
• REFERENCES

DEPENDENCIES

• Python-specific
  • distutils
    • For installing the sample src/app module into the Python environment
    • This facilitates importing the app-under-test modules in tests codes
    • The alternative to not using this is to append src/app to sys.path
  • pytest
    • For creating and running the tests
  • pytest-cov
    • For gathering and reporting code coverage
  • For other example-specific dependencies, see requirements.txt.
• Gitlab-specific
  • Access to a Gitlab instance
  • Access to a build/test/server PC for gitlab-runner

SETUP

• Configure the app installation in setup.py (reference)
• Configure the tests configuration in pytest.ini (reference)
• Configure the coverage collection in .coveragerc (reference)
• Setup a local testing environment
  • Using a virtual environment
    • Create/Activate a virtual environment

      $ python3.8 -m venv "~/.venvs/samples"
      $ source ~/.venvs/samples/bin/activate
      (samples) $ python -V
      Python 3.8.5
      
      
    • Install dependencies

      (samples) $ pip install -r requirements.txt
      
      
    • Install the app as a module in editable mode

      (samples) $ pip install -e .
      (samples) $ python
      ...
      >>> from app.models.stack import Stack
      >>> ss = Stack()
      
      
  • Using a Docker container
    • Build a Docker image using the Dockerfile

      $ docker build --tag sample-ci-python:3.8 .
      
      
    • Start the container

      $ docker run -it sample-ci-python:3.8 /bin/bash
      root@7648c3c82d32:/workspace#
      root@27f8a8b7be41:/workspace# ls -al
      total 36
      drwxr-xr-x 1 root root 4096 Aug  1 07:16 .
      drwxr-xr-x 1 root root 4096 Aug  1 07:16 ..
      -rw-r--r-- 1 root root   66 Aug  1 06:11 .coveragerc
      -rw-r--r-- 1 root root  266 Aug 12  2019 .gitlab-ci.yml
      -rw-r--r-- 1 root root  223 Aug  1 06:27 pytest.ini
      -rw-r--r-- 1 root root  393 Aug  1 06:09 requirements.txt
      -rw-r--r-- 1 root root  288 Aug  1 05:57 setup.py
      drwxr-xr-x 1 root root 4096 Aug  1 06:14 src
      drwxr-xr-x 3 root root 4096 Aug  1 05:56 tests
      root@27f8a8b7be41:/workspace# python
      Python 3.8.2 (default, Feb 26 2020, 14:58:38)
      [GCC 8.3.0] on linux
      Type "help", "copyright", "credits" or "license" for more information.
      >>> from app.models.stack import Stack
      >>> ss = Stack()
      
      
• Setup Gitlab CI
  • Install a Gitlab Runner on a publicly-accessible machine
  • Register the Runner with your Gitlab instance
    • Get the coordinator URL and registration tokens:
      • For shared runners: http://your/gitlab/instance/admin/runners
      • For project-specific runners: http://your/gitlab/project/settings/ci_cd
    • Use Docker as the executor (see ISSUES section on possible disk space issue)
    • Set project-specific tags
  • Configure the CI configuration in .gitlab-ci.yml
    • Set which Docker image and services to use
    • Set the tags
    • Set the commands for before_script and script
    • For other configurations, see GitLab CI/CD Pipeline Configuration Reference
  • Configure the Gitlab Runner at Gitlab project > Settings > CI/CD
    • Select Disable AutoDevOps to explicitly require .gitlab-ci.yml
    • Enable the runner only for "important" commits
      • Enable only on tagged jobs
      • Enable only on protected branches (ex. develop, master)
    • Set other options such as Timeout, Custom CI config path, and Triggers
    • Sample Configuration:

USAGE

• Run the tests
  • From the virtual environment or from the Docker container

    $ python -m pytest
    ==================== test session starts ====================
    platform linux -- Python 3.8.2, pytest-6.0.1, py-1.9.0, pluggy-0.13.1 -- /usr/local/bin/python
    cachedir: .pytest_cache
    rootdir: /workspace, configfile: pytest.ini, testpaths: tests
    plugins: cov-2.10.0
    collected 3 items
    
    tests/model_tests/stack_test.py::constructor_test PASSED    [1/3]
    tests/model_tests/stack_test.py::push_test PASSED           [2/3]
    tests/model_tests/stack_test.py::pop_test PASSED            [3/3]
    
    ----------- coverage: platform linux, python 3.8.2-final-0 -----------
    Name                         Stmts   Miss Branch BrPart  Cover
    --------------------------------------------------------------
    src/app/__init__.py              0      0      0      0   100%
    src/app/models/__init__.py       0      0      0      0   100%
    src/app/models/stack.py         12      0      0      0   100%
    --------------------------------------------------------------
    TOTAL                           12      0      0      0   100%
    Coverage HTML written to dir coverage
    
    
    ==================== 3 passed in 0.08s ==========================
    
    
  • From Gitlab
    • Make changes to the codes in src/app and/or in tests
    • Make changes to the .gitlab-ci.yml configuration (if necessary)
    • Commit the changes then push to Gitlab
    • Go to your Gitlab project > CI/CD > Pipelines
    • Select the currently running job to view progress/result
• Get the code coverage report
  • From the generated coverage directory in the same level as src and tests

    (samples) sample-ci-python$ tree -L 1 .
    .
    ├── Dockerfile
    ├── README.md
    ├── coverage      <-----------------------
    ├── docs
    ├── pytest.ini
    ├── requirements.txt
    ├── setup.py
    ├── src
    └── tests
    
    
  • From the downloadable artifacts of the CI job

ISSUES

• pytest uses cached codes instead of latest
  • Clear the pytest cache with --cache-clear
  • Optionally, also clear the generated __pycache__
• "This job is stuck, because you don’t have any active runners that can run this job."
  • Make sure that the .gitlab-ci.yml has the correct tags
  • Make sure the gitlab-runner service is running
  • Make sure the machine running gitlab-runner is accessible by the Gitlab instance
• "yaml invalid"
  • Go to the Gitlab project > CI/CD
  • On the top-right portion, click the CI Lint button
  • Paste the contents of gitlab-ci.yml file and validate
• The jobs are not running on the same runner/environment
  • Example: 1 job for build, 1 job for tests
  • As of now, Gitlab CI does not support this:
    • Sticky Runners
    • Caching general build artifacts between stages
    • Force all pipeline jobs to execute on same concurrent runner
  • The current workaround now is to use before_script to build and a job for tests
• The gitlab-runner is leaving a lot of -cache- containers/volumes
  • See a discussion of this behavior here
  • Possible solutions:
    • Manually regularly run docker system prune
    • Setup a cron job docker system prune -f

      # Cleanup docker containers/volumes every 3am every monday
      0 3 * * 1 /usr/bin/docker system prune -f
      
      

REFERENCES

• On Setting-Up the App with distutils
  • Writing the Setup Script
• On Setting-Up the Tests with pytest
  • Configuration Options
  • Invoking pytest
  • Good Integration Practices
  • How to Setup Files/Folders
  • How to Add src to sys.path
  • How to Add src/* packages
• On Setting-Up code coverage with pytest-cov
  • Configuration Reference
• On Setting-Up Gitlab CI
  • Getting started with GitLab CI
  • Installing a Gitlab Runner
  • Registering a Gitlab Runner
  • Configuring a Gitlab Runner
  • .gitlab-ci.yml Reference
  • Job Artifacts
• On Setting-Up a Docker Registry
  • Deploy a registry server
  • Test an insecure registry