docker-images-vs-containers-complete-beginners-guide

docker-images-vs-containers-complete-beginners-guide

What is the docker, and how would you use it in a system engineering role ?

Docker is a platform that allows developers and system administrators to package applications and their dependencies into containers. Containers are lightweight, portable and run consistently across different computing environment.

How docker is used in system engineering:

1. Containerization: Docker packages an application with all its dependencies into a single container, which can be run on any system that supports docker. This simplifies deployment and eliminate dependency conflicts.

2. Environment Isolation: Each containers is isolated, providing a consistent environment for applications regardless of the underlying host system. This helps with environment replication across development, stagging and production.

3. CI/CD pipelines: (Continuous Integration and Continuous Delivery/Development) Docker containers are widely used in CI/CD  pipelines to ensure consistent testing, building and deployment environment.

4. Scalability: Dockers containers can be easily scaled up or down in a Kubernetes or docker swarm environment.

Core components of Docker

It is responsible for the overall functioning of the docker platform and docker engine is a client-server based application and consists of 3 main components.

- Server
- REST API
- Client


- Server -> The server runs a daemon known as dockerd (Docker Daemon), which is nothing but a process. It is responsible for creating and managing docker images, containers, networks and volumes on the Docker platform.

- REST API - The REST API specifies how the applications can interact with the server and instruct it to get their job done.

- The client is nothing but a command line interface, that allows users to interact with docker using the commands.

Docker Terminology 

Docker Images and Docker containers are the two essential things that you will come across daily while working with docker.

In simple terms, a docker image is a template that contains the application, and all the dependencies required to run that application on docker.

On the other hand, as started earlier, a docker container is a logical entity. In more precise terms, it is a running instance of the docker image.

What is Docker Hub? 

Docker hub is the official online repository where you could find all the docker images that are available for us to use also allows us to store and distribute our custom images as well if we wish to do so. We could also make them either public or private, based on our requirements.


What is Docker image?

Docker image is actually an executable file that file inside instruction for which types of container we should make so using one image we can create multiple container.

Image is basically like a static screenshot or static snapshot of what the code and the dependencies or what the local development environment look like.

The relation between Docker and Container like the same as Class (class - how look like object create a blueprint of code) and Object in between of relation.

Docker image is giving a blue print of how container look like in MAC, Linux, Windows.

Container 

Docker is platform or services that useful for creating a container. container i

• Portable - Portable means we can share data one machine to another machine is become to easier share code as well as dependencies with their development team.
• Lightweight - Lightweight means easier to build, update and destroy and if we want install extra addon dependencies then we can install in same container.

OR

why we make container so what should i do for making container ?

• Containers are standardized software units that package code and dependencies together, ensuring an application runs quickly and reliably across any computing environment.

after making Docker Container and add some dependencies or else so we should make again docker image ?

Yes, you need to create a new image if you want to save those changes permanently. Containers are temporary and disposable. Any changes you make directly inside a running container will be lost forever if that container is stopped, deleted, or restarted.


You have two main ways to handle this, depending on your goal:

Method: Save the Live Container (Quick Fix)

If you spent a lot of time configuring a running container manually and do not want to lose your work immediately, you can take a snapshot of it.

Find your running container ID:

• bashdocker ps

Use code with caution.Commit the changes to create a brand new image directly from that running container:

• bashdocker commit CONTAINER_ID your-new-image-name

How to install and run docker desktop

Step 1: Check Requirements

Option A: Docker Desktop (Recommended)

Requirements:

• Windows 10 64-bit
• At least 4 GB RAM (8+ GB recommended)
• Hardware virtualization enabled in BIOS
• WSL 2 support

First, open PowerShell as Administrator and check:

systeminfo


Look for:

• Hyper-V Requirements: Yes
• Virtualization Enabled In Firmware: Yes

Step 2: Enable WSL 2

Open PowerShell as Administrator:

wsl --install

After completing task 1 like according to image 1(above image) it will ask for reboot the system then after rebooting the system (according to image 2 - below) it will automatically popup a cmd and run this wsl linux.

Restart your PC.

Verify:

wsl --status

You should see WSL version 2 installed.

Step 3: Download Docker Desktop

Go to:

Docker Desktop for Windows

Download the installer.

Step 4: Install Docker Desktop

Run the installer.

During installation:

✅ Use WSL 2 instead of Hyper-V (recommended)
✅ Add Docker Desktop shortcut

Restart if prompted.

Step 5: Start Docker

Launch Docker Desktop.

Wait until Docker reports:

• Docker Engine running

Step 6: Verify Installation

Open PowerShell:

• docker --version

Example output:

• Docker version 28.x.x

Check Docker engine:

• docker info

NOTE -  some useful URLs you can check here  

• https://hub.docker.com/_/hello-world
• https://app.docker.com/accounts/whoiskumaratul

Step 7: Run Your First Container

To run this your first container hello world docker from URL - you can check here - Docker Hello World 

Test Docker with:

• docker run hello-world

If successful, you'll see a welcome message.

So, for this we will pull first - docker pull hello-world

 Then run container and you can see in the docker desktop UI there will be create docker image and docker container 

• docker run hello-world

Docker Ubuntu

When we installed wsl ubuntu you have noticed in your local directory - linux section is there 

 you can run this via Linux ubuntu - try this command docker run -it ubuntu 

 -it -> we want to run in interactive mode

 Now we can check directory and create new folder, file because we are in linux directory 

Stop container

• docker stop <container_id>

Remove container

• docker rm <container_id>

Remove image

• docker rmi <image_name>

Step 8: Run an Nginx Web Server

Pull and run Nginx:

• docker run -d -p 8080:80 nginx

Verify:

• docker ps

Open browser:

• http://localhost:8080

You should see the Nginx welcome page.

Essential Docker Commands for Interviews

List running containers

• docker ps

List all containers

• docker ps -a

List images

• docker images

Stop container

• docker stop <container_id>

Remove container

• docker rm <container_id>

Remove image

• docker rmi <image_name>

Disclaimer