Docker Concepts Explained

Before building applications with Docker, it's important to understand the core concepts that make up the Docker ecosystem.

Images

An image is a read-only template used to create containers.

Popular images include:

• nginx
• ubuntu
• node
• redis
• postgres

View local images:

docker images

Containers

A container is a running instance of an image.

Example:

docker run nginx

List running containers:

docker ps

Dockerfile

A Dockerfile contains instructions used to build an image.

Example:

FROM node:20

WORKDIR /app

COPY . .

RUN npm install

CMD ["npm", "start"]

Build an image:

docker build -t my-app .

Registries

Registries store and distribute Docker images.

Popular registries:

• Docker Hub
• GitHub Container Registry
• Amazon ECR

Pull an image:

docker pull nginx

Volumes

Volumes provide persistent storage for containers.

Without volumes:

• Data is deleted when the container is removed.

With volumes:

• Data survives container recreation.

Create a volume:

docker volume create app-data

Networks

Networks allow containers to communicate with one another.

View available networks:

docker network ls

Create a custom network:

docker network create app-network

Putting Everything Together

A typical Docker workflow looks like this:

1. Write a Dockerfile.
2. Build an image.
3. Run a container.
4. Store data using volumes.
5. Connect services through networks.
6. Push images to a registry.

Summary

Docker is built around a few key concepts:

• Images
• Containers
• Dockerfiles
• Registries
• Volumes
• Networks

Understanding these fundamentals makes learning advanced Docker topics much easier.