Docker Fundamentals on Amazon EC2: A Practical Introduction

Source: Dev.to

Let’s Start with a Simple Story

Imagine this.

A developer builds an application on their laptop. It runs perfectly. Feeling confident, they send it to the testing team.

But then comes the message:

“The app is not working on our server.”

The developer checks everything and replies:

“But it works on my machine!”

If this sounds familiar, you’ve just met one of the biggest problems in software development.

What Actually Went Wrong?

The application depended on:

• A specific version of a programming language
• Certain libraries and tools
• Configuration files set up on the developer’s laptop

The server had a slightly different setup—and that was enough to break the app.

🐳 Enter Docker

Docker steps in like a smart packaging system. Instead of sending just the application code, Docker packs the app together with everything it needs to run—the runtime, libraries, and configurations—into a single unit called a container.

Now when the app moves:

• From laptop → test server
• From test server → production
• From local system → cloud

…it behaves exactly the same everywhere.

Think of Docker Like This

Imagine you’re sending a homemade dish to a friend. Instead of sending just the recipe and hoping they have the right ingredients and stove, you send the entire ready‑to‑eat meal in a sealed box. That’s Docker.

Install Docker on EC2

1. Launch an EC2 instance with an Amazon Linux AMI and connect via Instance Connect.
2. Run the following commands:

sudo yum update -y
sudo yum install docker -y
sudo systemctl start docker
sudo systemctl enable docker
sudo usermod -aG docker ec2-user  # Allow running Docker without sudo

Verify Docker Installation

docker --version

Exit and reconnect to the EC2 instance, then run:

docker ps  # Should return an empty list

Running a Container

The docker run command creates and starts a container from a specified image. For example, to start a Redis container:

docker run redis

If the Redis image is not present locally, Docker pulls it from Docker Hub automatically. Subsequent runs use the cached image.

Counting Containers

• List running containers:

  docker ps

• List all containers (including stopped ones):

  docker ps -a

Stopping a Container

docker stop <container-id-or-name>

Removing a Container

Note: Containers must be stopped before they can be removed.

docker rm <container-id-or-name>

Counting Images

docker images

Pulling an Image

docker pull <image-name>:<tag>

If no tag is specified, Docker pulls the latest tag by default.

Deleting an Image

First ensure no containers are using the image (stop and remove them). Then run:

docker rmi <image-id-or-name>

Running a Container in Detached Mode

Add the -d flag to run in the background:

docker run -d <image-name>
docker run -d --name=webapp1 nginx:1.14-alpine

Hosting a Local Registry

docker run -d --name my-registry -p 80:5000 --restart always registry:2

Pulling the Nginx Image

docker pull nginx:latest

Tagging an Image with a New Name

docker image tag nginx:latest localhost:80/nginx:latest

Pushing the Image

docker push localhost:80/nginx:latest

Verifying the Image Was Pushed

curl -X GET localhost/v2/_catalog

Port Mapping for Web Applications

Expose the application externally by mapping a host port to the container’s port with the -p option:

docker run -d --name=flask -p 80:80 nandinivijayr/myflaskapplication

The above command maps container port 80 to host port 80 and runs the container in detached mode.

Inspecting Containers and Images

Retrieve detailed JSON configuration for a container:

docker inspect <container-id-or-name>

Retrieve detailed JSON configuration for an image:

docker inspect <image-id-or-name>

Retrieving Container Logs

docker logs <container-id-or-name>

Question Time

Run a MySQL container and give it a name of your choice.