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Aisalkyn Aidarova
Aisalkyn Aidarova

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Full Lecture Part 1: Understanding Docker from an Enterprise Perspective

Most beginners learn Docker as:

docker run nginx
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and think they know Docker.

A DevOps Engineer with 6 years of experience sees Docker very differently.

Docker is not just a tool to run containers.

Docker is:

  • Application packaging technology
  • Infrastructure standardization technology
  • Deployment technology
  • CI/CD technology
  • Resource optimization technology
  • Cloud-native foundation

Today almost every company using:

  • AWS ECS
  • AWS EKS
  • Kubernetes
  • Azure AKS
  • Google GKE

is using Docker concepts underneath.

Before learning commands, you must understand why Docker exists.

The Problem Before Docker

Imagine a company in 2012.

The development team creates a Java application.

The application works perfectly on the developer's laptop.

The developer gives the code to Operations.

Operations deploys it to production.

Suddenly:

Application Failed
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Developer says:

It works on my machine.
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Operations says:

It doesn't work in production.
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This became one of the biggest problems in software engineering.

Why?

Because every machine was different.

Developer Laptop:

Ubuntu 22
Java 17
Maven 3.9
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Production Server:

Ubuntu 18
Java 11
Maven 3.6
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Different libraries.

Different versions.

Different dependencies.

Different configurations.

Result:

Deployment Failure
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This happened thousands of times every day across the industry.

Docker was created to solve this problem.

What Exactly Is Docker?

Docker packages everything an application needs into a single package.

Think of Docker as a shipping container.

Before shipping containers:

Boxes
Chairs
Tables
Electronics
Food
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Everything was loaded differently.

Shipping was slow.

Shipping was expensive.

Shipping was difficult.

Then shipping containers were invented.

Now everything goes inside one standard container.

No matter what is inside.

A truck can move it.

A train can move it.

A ship can move it.

Same idea with Docker.

Docker creates a standardized container for software.

Inside that container:

Application
Libraries
Dependencies
Runtime
Configuration
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Everything needed to run.

Visualizing Docker

Think about a NodeJS application.

Without Docker:

Developer Laptop
|
NodeJS
Express
Libraries
Configuration
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Production:

Production Server
|
NodeJS
Express
Libraries
Configuration
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Everything must be installed again.

Now Docker:

Docker Image
|
NodeJS
Express
Libraries
Configuration
Application
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Build once.

Run anywhere.

What Is a Container?

This is the most common interview question.

A container is NOT Docker.

A container is NOT an image.

A container is:

A running process
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Think of this carefully.

When you start Chrome:

Chrome Process
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When you start VS Code:

VS Code Process
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When Docker starts a container:

Container Process
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A container is simply a process isolated from other processes.

What Makes Containers Special?

Linux provides special technologies:

Namespaces

Namespaces create isolation.

Container A sees:

Its own processes
Its own network
Its own filesystem
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Container B sees:

Its own processes
Its own network
Its own filesystem
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Even though both run on the same server.

Control Groups (cgroups)

Cgroups control resources.

Example:

Container A:

2 CPUs
4GB RAM
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Container B:

1 CPU
2GB RAM
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Linux ensures containers stay inside those limits.

As a DevOps Engineer you will use this daily.

Why Containers Are Better Than Virtual Machines

Let's compare.

Traditional Virtual Machine:

Physical Server
|
Hypervisor
|
VM1 -> Guest OS
VM2 -> Guest OS
VM3 -> Guest OS
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Each VM has:

Linux Kernel
System Services
Libraries
Application
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Huge amount of duplication.

Container Model:

Physical Server
|
Host Linux
|
Docker Engine
|
Container A
Container B
Container C
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All containers share:

Host Kernel
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Result:

Faster

VM:

2-5 minutes startup
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Container:

2-10 seconds
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Smaller

VM:

10-20 GB
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Container:

100 MB
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More Efficient

One server may run:

20 VMs
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or

100+ Containers
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depending on workload.

This is why companies adopted containers.

Docker Architecture

When you type:

docker run nginx
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many things happen.

Docker Client

The command line.

Example:

docker run
docker build
docker pull
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This is only the interface.

Docker Daemon

The actual engine.

Service running in background:

dockerd
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Receives requests.

Creates containers.

Creates networks.

Creates volumes.

Pulls images.

Docker Registry

Stores images.

Examples:

Think:

GitHub stores code

Registry stores images
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What Is a Docker Image?

A Docker image is a blueprint.

Not running.

Not active.

Just instructions.

Example:

Ubuntu Image
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contains:

Ubuntu Filesystem
Libraries
Packages
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Still not running.

Example:

When you buy a house blueprint:

Blueprint ≠ House
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Same concept:

Image ≠ Container
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Image vs Container

Image:

Template
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Container:

Running Instance
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Example:

One image:

nginx
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Can create:

Container1
Container2
Container3
Container4
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Exactly like:

One blueprint
Many houses
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How a DevOps Engineer Uses Docker Daily

A developer writes code.

Example:

React
NodeJS
Java
Python
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DevOps engineer creates:

Dockerfile
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Dockerfile describes:

How to build application
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Then:

docker build
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creates image.

Then:

docker push
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pushes image into registry.

Then:

ECS
Kubernetes
EKS
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pull image and deploy.

This is the heart of modern CI/CD.

Enterprise Flow

Real production architecture:

Developer
     |
GitHub
     |
Jenkins/GitHub Actions
     |
Docker Build
     |
Docker Image
     |
ECR
     |
ECS/EKS
     |
Application Running
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Every major company follows this concept.

As a senior DevOps engineer you must understand:

  1. How images are built
  2. How containers run
  3. How networking works
  4. How storage works
  5. How security works
  6. How orchestration works
  7. How monitoring works
  8. How troubleshooting works

These topics are what separate a junior Docker user from a 6-year DevOps engineer.

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