What is Docker?

Introduction to Docker

Docker has changed the way developers build, package, and deploy applications. It allows applications to run in isolated environments called containers, making it easier to manage dependencies and ensure consistency across different environments. In this blog, we will explore what Docker is, its key features, and commonly used Docker commands.

What is Docker?

Docker is an open-source platform that enables developers to automate the deployment of applications inside lightweight, portable containers. Unlike traditional virtual machines, Docker containers share the host OS kernel, making them more efficient and faster to start. With Docker, applications can run consistently across various environments, from development to production.

Features of Docker

1. Lightweight and Fast

• Docker containers share the host OS kernel, eliminating the need for a full-fledged OS in each container.
• Containers start quickly compared to virtual machines.

2. Portability

• Containers run consistently across different environments, such as local machines, cloud servers, and CI/CD pipelines.
• The "Build once, run anywhere" philosophy reduces compatibility issues.

3. Isolation

• Each container runs in an isolated environment with its own dependencies, libraries, and runtime.
• Prevents conflicts between different applications running on the same system.

4. Scalability

• Docker makes it easy to scale applications by running multiple containers in parallel.
• Works seamlessly with orchestration tools like Kubernetes for managing containerized applications.

5. Efficient Resource Utilization

• Since containers share the host OS kernel, they use fewer resources compared to traditional virtual machines.

6. Simplified Dependency Management

• Docker images package all required dependencies, ensuring consistent application behavior across environments.

Essential Docker Commands

1. Docker Installation Verification

docker --version

Checks the installed Docker version.

2. Pulling an Image from Docker Hub

docker pull <image-name>

Example:

docker pull nginx

Downloads the latest Nginx image from Docker Hub.

3. Listing Available Images

docker images

Displays all downloaded Docker images on the system.

4. Running a Container

docker run -d -p 8080:80 --name my-nginx nginx

Runs an Nginx container in detached mode and maps port 8080 on the host to port 80 in the container.

5. Listing Running Containers

docker ps

Shows all running containers.

6. Listing All Containers (Including Stopped)

docker ps -a

Displays all containers, including stopped ones.

7. Stopping a Running Container

docker stop <container-id>

Stops a running container by its ID or name.

8. Removing a Container

docker rm <container-id>

Deletes a stopped container.

9. Removing an Image

docker rmi <image-id>

Removes a Docker image from the system.

10. Building a Docker Image

docker build -t my-app .

Builds a Docker image using the Dockerfile in the current directory and tags it as "my-app".

11. Executing a Command Inside a Running Container

docker exec -it <container-id> /bin/bash

Opens a bash shell inside the running container.

12. Checking Docker Logs

docker logs <container-id>

Displays logs generated by a running container.

13. Pruning Unused Docker Resources

docker system prune -a

Cleans up unused images, containers, and networks to free up space.

Conclusion

Docker simplifies application development, deployment, and scaling by providing a lightweight and consistent environment. Its portability, efficiency, and ease of use make it an essential tool for modern software development. By mastering Docker commands, developers can streamline their workflow and build reliable applications with minimal overhead.

If you are new to Docker, start by installing it and experimenting with basic commands. As you gain experience, you can explore more advanced concepts like Docker Compose, networking, and container orchestration with Kubernetes.