Introduction
Brief Overview of Docker
Docker is a platform that allows developers to package applications and their dependencies into a standardized unit called a container. Containers are lightweight, portable, and can run on any environment that supports Docker, ensuring consistency across development, testing, and production environments.
Importance of Docker in DevOps
Docker plays a crucial role in DevOps by enabling continuous integration and continuous deployment (CI/CD). It helps streamline the software development lifecycle, reduce conflicts between different development environments, and improve scalability and resource utilization.
Getting Started with Docker
What is Docker?
Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Containers allow a developer to package up an application with all parts it needs, such as libraries and other dependencies, and ship it all out as one package.
Key Concepts
- Images: Read-only templates used to create containers. They are built from Dockerfiles.
- Containers: Running instances of Docker images. They are isolated from the host system and other containers.
- Dockerfile: A text file that contains instructions for building a Docker image.
Setting Up Docker
Installing Docker
To install Docker, follow the instructions for your operating system on the Docker installation page.
Basic Docker Commands
-
docker run
: Run a container from an image. -
docker build
: Build an image from a Dockerfile. -
docker images
: List all Docker images on your system. -
docker ps
: List all running containers.
Integrating Docker with GitLab CI/CD
Overview of CI/CD
CI/CD is a method to frequently deliver apps to customers by introducing automation into the stages of app development. The main concepts attributed to CI/CD are continuous integration, continuous deployment, and continuous delivery.
Benefits of Using Docker in CI/CD Pipelines
- Consistency: Ensures the same environment in development, testing, and production.
- Scalability: Easily scale applications horizontally.
- Isolation: Each container runs in isolation, which reduces conflicts and improves security.
Step-by-Step Guide
Setting Up a GitLab Project
- Create a GitLab Account: Sign up at GitLab.
-
Create a New Project:
- Click on the "New Project" button.
- Select "Create blank project".
- Fill in the project name (e.g.,
DockerCIPipeline
), description (optional), and set the visibility level. - Click "Create project".
Writing a Dockerfile
Create a file named Dockerfile
in your project directory with the following content:
# Use an official Python runtime as a parent image
FROM python:3.8-slim
# Set the working directory
WORKDIR /app
# Copy whats in app.py
COPY . /app
# Install pkgs specified in requirements.txt
RUN pip install --no-cache-dir -r requirements.txt
# Make port 80 available to the world outside this container
EXPOSE 80
# Define environment variable
ENV NAME World
# Run app.py when the container launches
CMD ["python", "app.py"]
Creating a .gitlab-ci.yml File for Docker Integration
Create a .gitlab-ci.yml
file in your project directory with the following content:
stages:
- build
- push
variables:
DOCKER_DRIVER: overlay2
IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
build_image:
stage: build
image: docker:latest
services:
- docker:dind
script:
- docker build -t $IMAGE_TAG .
- echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER --password-stdin $CI_REGISTRY
- docker tag $IMAGE_TAG $CI_REGISTRY_IMAGE:latest
push_image:
stage: push
image: docker:latest
services:
- docker:dind
script:
- echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER --password-stdin $CI_REGISTRY
- docker push $IMAGE_TAG
- docker push $CI_REGISTRY_IMAGE:latest
Pushing Docker Images to GitLab's Container Registry
-
Set Up CI/CD Variables:
- Go to your GitLab project.
- Navigate to Settings > CI/CD > Variables.
- Add the following variables:
-
CI_REGISTRY
: Your GitLab container registry URL. -
CI_REGISTRY_USER
: Your GitLab username. -
CI_REGISTRY_PASSWORD
: Your GitLab access token (create one from your GitLab profile settings).
-
Commit and Push Changes:
git add Dockerfile .gitlab-ci.yml
git commit -m "Add Dockerfile and CI/CD pipeline configuration"
git push origin main
Monitoring and Verification
Monitor the Pipeline:
- Go to your GitLab project page.
- Navigate to CI/CD > Pipelines.
- You should see a new pipeline triggered by your recent push.
- Click on the pipeline to monitor its progress and view job logs.
Verify Docker Image:
- After the pipeline completes, go to Packages & Registries > Container Registry in your GitLab project.
- You should see your Docker image listed there.
Conclusion
Recap of Key Points:
- Docker containers offer a consistent, isolated environment for your applications.
- GitLab CI/CD pipelines can be configured to build and push Docker images automatically.
- Monitoring and verifying pipelines and Docker images ensure a smooth CI/CD process.
Next Steps:
- Explore advanced Docker features like multi-stage builds.
- Integrate more complex testing frameworks.
- Experiment with deploying Docker containers to cloud platforms.
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