How is the automation of application deployment in Kubernetes implemented using GitLab CI/CD?

Automating application deployment in Kubernetes with GitLab CI/CD typically involves the following steps:

1. Setting up GitLab Runner — runs pipelines and has access to the Kubernetes cluster.

2. Creating .gitlab-ci.yml — a file that describes the stages and jobs for building, testing, and deploying.

3. Building and publishing the container image — during one of the build stages, the application's Docker image is built and pushed to a registry (GitLab Container Registry or another).

4. Deploying to Kubernetes — using kubectl or Helm in the pipeline, Kubernetes manifests are applied to update the deployment with the new image.

5. Using environment variables and secrets — for storing configurations and access to the cluster.

Example of a simple .gitlab-ci.yml for deployment:

stages:
  - build
  - deploy

build_image:
  stage: build
  image: docker:latest
  services:
    - docker:dind
  script:
    - docker build -t registry.gitlab.com/your_project/image:$CI_COMMIT_SHA .
    - docker push registry.gitlab.com/your_project/image:$CI_COMMIT_SHA
  only:
    - main

deploy_to_k8s:
  stage: deploy
  image: bitnami/kubectl:latest
  script:
    - kubectl set image deployment/your-deployment your-container=registry.gitlab.com/your_project/image:$CI_COMMIT_SHA
    - kubectl rollout status deployment/your-deployment
  only:
    - main

Thus, when pushing to the main branch, the image is built, published, and the application in Kubernetes is updated automatically.