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.
Docker Learning Path for You
Week 1
- Install Docker
- Containers vs Images
- Pull images
- Run containers
- Port mapping
Week 2
- Dockerfile
- Build custom images
- Environment variables
Week 3
- Docker Volumes
- Docker Networks
- Multi-container
- applications
Week 4
- Docker Compose
- Deploy React/Node applications
- Container troubleshooting
But we will start from week 1 module and try to answer the interview level
question also
Install Docker
For installing the docker via docker-desktop and via wsl linux. you can choose any of the them or both so check it here for previously we have done this part and many things you can learn from other blog article.
Click Here
Containers vs Images
This is one of the most common Docker
interview questions.
- Docker Image
An Image is like a blueprint or template.
Think of it like:
Windows ISO File
↓
Install Windows
↓
Running Windows OS
Similarly:
Docker Image
↓
Run Image
↓
Docker Container
Examples of Images:
- nginx
- ubuntu
- mysql
- node
View downloaded images:
- docker images
Example output:
Docker Container
A Container is a running instance of an image or Containers are
standardized software units that package code and dependencies together,
ensuring an application runs quickly and reliably across any computing
environment.
Example:
- docker run nginx
Docker:
- Checks for nginx image
- Downloads it if missing
- Creates container
- Starts container
View running containers: list running container and
verify
docker ps
Interview Answer
What is the difference between Image and Container?
Image
- Read-only template
- Used to create containers
- Similar to an ISO file
Container
- Running instance of an image
- Has its own process and network
- Similar to an installed/running operating system
Pull Images
What is Pull?
Downloading an image from Docker
Hub to your local machine.
Example:
docker pull
nginx
Docker downloads:
- nginx:latest
- Pull Ubuntu
- docker pull ubuntu
Check downloaded images:
- docker images
- Pull Specific Version
- docker pull nginx:1.27
Why?
In production we often use specific versions instead of latest.
Interview Question
What does docker pull do?
Answer:
docker pull downloads an image from a registry such as Docker
Hub to the local Docker host.
like this hello-world repo or
registry -
Port Mapping
This is extremely important.
Without Port Mapping
Run nginx:
- docker run nginx
- Container runs internally.
- You cannot access it from your browser.
With Port Mapping
- docker run -d -p 8080:80 nginx
Meaning:
- Host Machine Port = 8080
- Container Port = 80
Visualization:
Your Laptop
localhost:8080
│
▼
Docker
Container
Port 80 (Nginx)
Test
Open browser:
http://localhost:8080
You should
see:
Welcome to nginx!
Another Example
Node.js app running on port 3000 inside container:
- docker run -d -p 3000:3000 myapp
Meaning:
- Host 3000 → Container 3000
- Check Port Mapping
- docker ps
Example:
PORTS
- 0.0.0.0:8080->80/tcp
Meaning:
Host Port 8080
↓
Container Port 80
Commands You Must Remember
Pull image:
- docker pull nginx
List images:
- docker images
Run container:
- docker run nginx
Run in background:
- docker run -d nginx
Port mapping:
- docker run -d -p 8080:80 nginx
Running containers:
- docker ps
All containers:
- docker ps -a
Before moving to Week 2, make sure you can confidently explain:
✅ What is Docker?
✅ What is an Image?
✅ What is a
Container?
✅ What is Docker Hub?
✅ What is docker pull?
✅
What is port mapping?
✅ Difference between docker ps and docker
images?
✅ Meaning of 8080:80?
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