Om's Brain

1 🐳 Docker

2 min read

🐳 Docker Components Explained

🛠️ Dockerfile

  • A text file that contains a set of instructions to build a Docker image
  • Specifies the base image, environment variables, commands to run, and files to copy
  • Each instruction creates a new layer in the Docker image
  • Example instructions: FROM, RUN, COPY, ENV, EXPOSE, CMD, etc.
  • Helps in automation and consistency across different environments

🖼️ Docker Image

  • A lightweight, standalone, and executable package that includes:
    • Code
    • Runtime
    • Libraries
    • Environment variables
    • System tools
  • Read-only (immutable) and layered, built from the Dockerfile
  • Can be inherited from a base image (like python:3.9 or ubuntu:20.04)
  • Stored in a registry, such as:
    • Docker Hub (public)
    • AWS ECR (Elastic Container Registry)
    • Azure Container Registry (ACR)

🐳 Docker Container

  • A running instance of a Docker image
  • Containers are isolated environments that run applications
  • Multiple containers can be created from the same image
  • Containers share the same kernel as the host machine but have their own file system, network, and processes
  • By default, a container only lives until the process inside is running (e.g., a Node.js app or Python script)

🔥 Container Lifecycle

  • docker run → Creates and starts a container
  • docker stop → Stops a running container
  • docker restart → Restarts a container
  • docker rm → Removes a container
  • docker logs → View container logs

📊 Docker Workflow

+---------------------------------------------------+
|              Dockerfile                           |
|---------------------------------------------------|
| - Base Image: Node:16-alpine                     |
| - ENV variables (NODE_ENV, PORT, DB_HOST)        |
| - Install dependencies                            |
| - Copy application code                           |
| - Expose port 3000                                |
| - CMD to run the app                              |
+---------------------------------------------------+
      ↓
      ↓  Docker Build Command
      ↓  `docker build -t myapp .`
+---------------------------------------------------+
|              Docker Image                         |
|---------------------------------------------------|
| - Contains code, runtime, libraries, env vars    |---> | Push to Docker Hub | ECR |
| - Layered structure                               |
| - Immutable and reusable                          |
| - Stored in Docker Hub or private registry       |
+---------------------------------------------------+
      ↓
      ↓  Docker Run Command
      ↓  `docker run -d -p 3000:3000 myapp`
+---------------------------------------------------+
|            Docker Container                       |
|---------------------------------------------------|
| - Running instance of the image                   |
| - Isolated environment                            |
| - Own file system, network, and processes        |
| - Runs app on port 3000                          |
| - Dies when process stops                         |
+---------------------------------------------------+

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