twtech Docker Containerization

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Docker Containerization

Docker is an open-source platform for developing, shipping, and running applications in containers. It allows developers to package applications with their dependencies, ensuring consistency across different environments.

 Key Concepts of Docker

1.1. What is a Container?

• A lightweight, isolated environment that includes the application, libraries, and dependencies.
• Runs consistently across different systems (laptops, servers, clouds).

1.2. Docker vs. Virtual Machines (VMs)

Feature	Docker Containers	Virtual Machines (VMs)
Speed	Fast startup (~seconds)	Slow startup (~minutes)
Size	Lightweight (MBs)	Heavy (GBs)
Isolation	Process-level isolation	Full OS-level isolation
Resource Usage	Shares host OS kernel	Requires full OS per VM
Portability	Runs anywhere	Limited to host OS compatibility

2. Benefits of Docker

Portability – Works on any system with Docker installed.
Consistency – Eliminates "it works on my machine" issues.
Efficiency – Uses fewer resources than VMs.
Scalability – Easily deployable in Kubernetes.
Faster CI/CD – Speeds up development and testing.

3. Docker Architecture

• Docker Client: The CLI tool used to interact with Docker.
• Docker Daemon (Engine): Runs containers and manages system resources.
• Docker Images: Pre-packaged application blueprints.
• Docker Containers: Running instances of Docker images.
• Docker Hub: Public/private registry for sharing images.

4. Essential Docker Commands

4.1. Install & Verify Docker

docker --version    # Check Docker version
docker info         # Get system info

4.2. Working with Images

docker pull nginx             # Download an image from Docker Hub
docker images                 # List downloaded images
docker rmi <image_id>         # Remove an image

4.3. Running Containers

docker run hello-world        # Run a test container
docker run -d -p 8080:80 twtech-springapp  # Run Nginx in detached mode, exposing port 80 on 8080
docker ps                     # List running containers
docker ps -a                  # List all containers (including stopped ones)
docker stop <container_id>     # Stop a running container
docker rm <container_id>       # Remove a stopped container

4.4. Building Custom Docker Images

docker build -t twtech-webapp .   # Build an image from a Dockerfile
docker tag twtech-webapp:v1 devopspatemf2021/twtech-webapp:v1  # Tag an image for a repository
docker push devopspatemf2021/twtech-webapp:v1  # Push image to Docker Hub

4.5. Container Management

docker logs <container_id>    # View logs of a container
docker exec -it <container_id> bash  # Access container shell
docker inspect <container_id>  # Get detailed container info

5. Dockerfile (Creating Custom Images)

A Dockerfile is a script with instructions to create a Docker image.

Example:

# Dockerfile

# Use base image
FROM node:18  

# Set working directory  
WORKDIR /app  

# Copy files and install dependencies  
COPY package.json .  
RUN npm install  

# Copy the rest of the app  
COPY . .  

# Expose port and define the startup command  
EXPOSE 80  
CMD ["node", "server.js"]  

To build and run:

docker build -t twtech-springapp .  
docker run -d -p 3000:80 twtech-springapp 

6. Docker Networking

docker network create mynetwork    # Create a custom network
docker network ls                  # List networks
docker network inspect mynetwork   # Inspect a network

7. Docker Volumes (Data Persistence)

docker volume create mydata         # Create a volume
docker run -v twtech-data:/app/data twtech-springapp  # Attach volume to a container
docker volume ls                     # List volumes

8. Kubernetes Integration

• Docker containers can be deployed in Kubernetes for orchestration and scaling.
• Kubernetes pods use Docker images to run applications.

9. Best Practices for Docker

Use lightweight base images (Alpine, Distroless).
Keep Docker images small by minimizing unnecessary dependencies.
Use .dockerignore to exclude files from image builds.
Tag images properly (e.g., myapp:v1, latest).
Scan images for security vulnerabilities (docker scan).