Quartz 4

Docker Introduction

3 min read

Docker

Docker is an open platform for developing, shipping, and running applications, allowing you to separate your applications from your infrastructure so you can deliver software quickly.

  • A standardized tool that helps run applications quickly and consistently, built on Linux container (LXC) technology
  • Allows you to reproduce the same environment anywhere with a single command, without manually configuring complex setups.
  • Almost all companies use Docker lol
    • Connected to DevOps, cloud, etc
    • Used a lot because Docker fundamentally solves the environment mismatch problem across Dev → Test → Stage → Prod.
  • Key Components
    • Image: A template that packages the entire runtime environment as code
    • (Docker) Container: An isolated process environment running based on an image
    • Dockerfile: A declarative script used to build images
    • Docker CLI / Daemon: Tools for building images, running containers, mounting volumes, managing networks, and more
  • After testing, remove all related images, they take sm space
  • Docker Commands
  • Docker Desktop (GUI)
    • a desktop application that helps developers run and manage Docker containers in a local environment
    • features
      • provides both Docker CLI + GUI tools
      • visualization
      • Includes features like Kubernetes, Volumes, and Networks
      • Offers an interface for resource limits, logs, and image management
    • But not used that often → CLI is more useful
      • Automation, writing scripts + full control
      • CI/CD pipelines, complex setups, etc
    • So GUI is mostly used for monitoring/quick checks

Docker image

  • It’s an image
  • A read-only template with instructions for creating a Docker container
    • It’s basically a package that includes all of the files, binaries, libraries, and configurations to run a container
    • Often, an image is based on another image, with some additional customization
    • You might create your own images or you might only use those created by others and published in a registry
    • To build your own image, you create a Dockerfile with a simple syntax for defining the steps needed to create the image and run it
  • Key properties of Docker images
    • Immutable → cannot be changed once built
    • Layered architecture → efficient caching and storage
    • Reusable → multiple containers can be launched from the same image

Docker Container

Overview

A runnable instance of a Docker image.

  • https://docs.docker.com/get-started/docker-concepts/the-basics/what-is-a-container/
  • General terms to understand Docker - Container (General Term)
    • A docker container is basically aspecific type of container created and managed by the Docker platform.
  • Characteristics
    • Created from Docker images
    • Provide isolation from other containers and the host
    • Lightweight, fast, and resource-efficient
    • Packaged at the application level (not the full system)
  • Example: Run Nginx in Docker
    • $ docker run -d -p 8080:80 nginx
    • This single command launches an Nginx server in a new containerized environment, without manual installation, setup, or firewall configuration.
  • You can have multiple containers (isolated environments / filesystems / network ports etc)
[Host OS]
 └── docker-engine
      ├── container-1 (/var/lib/docker/containers/abc123)
      └── container-2 (/var/lib/docker/containers/def456)

Tips

  • When writing Dockerfiles, structure COPY, RUN, and CMD clearly to make the best use of build caching.
  • Use a .dockerignore file to exclude unnecessary files from your Git repository (e.g., node_modules, .git) and improve build performance.
  • Leverage multi-stage builds to separate development dependencies from runtime binaries, reducing image size.
  • For Docker image security, enable vulnerability scanning in registries like Docker Hub or Harbor.
  • For team collaboration, standardize the development environment using docker-compose.

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