How to Build and Deploy a Python Flask App with GitLab CI/CD and Docker

1. Create a Python project

Clone the open‑source Flask demo from GitHub ( https://github.com/imooc-course/docker-cloud-flask-demo ) into a new GitLab project.

2. Manual deployment

Clone the project locally, build the Docker image, and run the container.

➜  [/Users/mac/PycharmProjects] git clone http://gitlab.example.com/root/flask-demo.git
Cloning into 'flask-demo'...
... (output omitted for brevity) ...
➜  [/Users/mac/PycharmProjects/flask-demo] docker build -t flask-demo .
➜  [/Users/mac/PycharmProjects/flask-demo] docker run -d -p 5000:5000 flask-demo

Open a browser and navigate to http://<i>your‑ip</i>:5000 to verify the service.

3. Deploy with GitLab CI/CD pipelines

Register three GitLab runners using Docker as the executor: one for Python 2.7, one for Python 3.4, and a shell runner tagged demo.

➜  [/Users/mac] gitlab-runner register
Runtime platform arch=amd64 os=darwin ...
Please enter the gitlab-ci coordinator URL:
http://gitlab.example.com/
Please enter the gitlab-ci token:
6-uZ1ndZ2NRGp8_TghnL
Please enter the gitlab-ci tags (comma separated):
python3.4
... (registration output) ...

➜  [/Users/mac] gitlab-runner register
... (similar steps for python2.7) ...

➜  [/Users/mac] gitlab-runner register
... (shell runner with tag demo) ...

Verify that the runners are alive:

➜  [/Users/mac] gitlab-runner verify
Verifying runner... is alive   runner=NkYLeMbb

3.1 Create .gitlab-ci.yml

stages:
    - style
    - test

pep8:
    stage: style
    script:
      - pip install tox
      - tox -e pep8
    tags:
      - python2.7

unittest-py27:
    stage: test
    script:
      - pip install tox
      - tox -e py27
    tags:
      - python2.7

unittest-py34:
    stage: test
    script:
      - pip install tox
      - tox -e py34
    tags:
      - python3.4

Commit and push the file; the pipeline automatically runs the style and test jobs.

git add .
git commit -m "add .gitlab-ci.yml"
git push -u origin master

In GitLab CI/CD > Pipelines you can see each job’s logs and verify that the Python 2.7 environment is ready.

4. Full CI/CD workflow

Protect the master branch (no direct pushes) and require successful pipelines before merge requests can be merged.

Create a dev branch, push changes, and open a merge request.

git fetch
git checkout dev
... (make changes) ...
git push origin dev

4.1 Private Docker registry

Run a local registry container:

docker run -d -v ~/registry:/var/lib/registry -p 5001:5000 --restart=always --name registry registry:2

Tag and push an image to the registry:

docker tag busybox registry.example.com:5001/busybox
docker push registry.example.com:5001/busybox

4.2 Extend .gitlab-ci.yml for deployment and release

stages:
    - style
    - test
    - deploy
    - release

pep8:
    stage: style
    script:
      - pip install tox
      - tox -e pep8
    tags:
      - python2.7
    except:
      - tags

unittest-py27:
    stage: test
    script:
      - pip install tox
      - tox -e py27
    tags:
      - python2.7
    except:
      - tags

unittest-py34:
    stage: test
    script:
      - pip install tox
      - tox -e py34
    tags:
      - python3.4
    except:
      - tags

docker-deploy:
    stage: deploy
    script:
      - docker build -t flask-demo .
      - if [ $(docker ps -aq --filter name=web) ]; then docker rm -f web; fi
      - docker run -d -p 5000:5000 --name web flask-demo
    tags:
      - demo
    only:
      - master

docker-images-release:
    stage: release
    script:
      - docker build -t registry.example.com:5001/flask-demo:$CI_COMMIT_TAG .
      - docker push registry.example.com:5001/flask-demo:$CI_COMMIT_TAG
    tags:
      - demo
    only:
      - tags

When a tag is pushed, the release job builds a versioned image and pushes it to the private registry, completing the CI‑based version release.