Installing Docker & Running Your First Real Container (Nginx Example)

Most tutorials stop at: “Run docker run nginx and you’re done.”

In real DevOps work, that’s not enough.

Today, we’ll:

• Install Docker properly
• Run an Nginx container
• Understand what’s actually happening
• Debug common beginner mistakes

⚙️ Installing Docker (Production Mindset)

On Linux (Most Common in Real Projects)

sudo apt update
sudo apt install docker.io -y
sudo systemctl start docker
sudo systemctl enable docker

Real-world check:

docker --version
docker info

If docker info fails → Docker daemon is not running.

👉 This is a very common CI/CD failure reason.

🧑‍💻 Common Beginner Issue (Very Real)

Problem:

Got permission denied while trying to connect to the Docker daemon socket

Why it happens:

Docker runs as root, but your user is not in the docker group.

Fix (Real DevOps Practice):

sudo usermod -aG docker $USER
newgrp docker

This issue appears frequently in:

• New servers
• CI agents
• Fresh EC2 instances

🚀 Running Your First Real Container (Nginx)

Now let’s run something meaningful:

docker run -d -p 8080:80 nginx

What this actually means:

• -d → Run in background (detached mode)
• -p 8080:80 → Map host port to container port
• nginx → Image name

🌐 Real-Time Verification

Check running containers:

docker p

Open browser:

http://localhost:8080

👉 If you see Welcome to nginx, your container is working.

🛠️ Real Troubleshooting Scenarios

❌ Browser not loading?

Check:

docker ps
docker logs <container_id>

Common causes:

• Port already in use
• Container exited
• Firewall blocking port

❌ Container stopped immediately?

Check logs:

docker logs <container_id>

Most of the time, it’s due to:

• Wrong image
• Wrong command
• Port conflicts

🧠 Important DevOps Concept (Early Learning)

Containers are ephemeral

If the container stops:

• Data is lost
• Logs may disappear
• Container must be recreated

This is why:

• Logs go to STDOUT
• Data goes to volumes (later topic)

🎯 Interview Alignment (Very Important)

Interview Question:

How do you run an application using Docker?

❌ Weak Answer:

I use docker run command.

✅ Strong Practical Answer:

First, I ensure Docker daemon is running. Then I run the container using docker run with proper port mapping. I verify using docker ps and docker logs. If the application is not accessible, I troubleshoot using logs, port conflicts, and container state.

This answer shows hands-on experience, not theory.

🧠 Day 3 Key Takeaways

• Installing Docker correctly matters
• Docker daemon issues are common in real projects
• docker run is only the start
• Logs and ports are your first debugging tools

👉 Next (Day 4): Docker Images vs Containers (Why Most Beginners Get This Wrong)