Understanding how Docker images are built and pushed in a CI/CD workflow.
Docker is a transformative technology for Continuous Integration and Continuous Deployment (CI/CD) pipelines. In a typical CI/CD workflow, when a developer pushes new code to a version control system like Git, it triggers an automated process. The CI (Continuous Integration) server (like Jenkins, GitLab CI, or GitHub Actions) checks out the code. The first key step is to build a Docker image from the application's Dockerfile. This encapsulates the application and all its dependencies into a single, immutable artifact. After the image is built, it's typically tagged with a unique identifier, such as the Git commit hash, to ensure traceability. The next step is to run automated tests against this newly created image. By running tests inside the container, you ensure that the testing environment is identical to the eventual production environment. If all tests pass, the CD (Continuous Deployment) part of the pipeline begins. The Docker image is pushed to a container registry (like Docker Hub, AWS ECR, or Google GCR). From there, the pipeline can trigger a deployment process that pulls the new image from the registry and updates the running application, often using a container orchestrator like Kubernetes to perform a rolling update. This workflow makes deployments faster, more reliable, and consistent across all environments.