Docker

Docker is a software platform that allows you to build, test, and deploy applications quickly. Docker packages software into standardized units called containers that have everything the software needs to run including libraries, system tools, code, and runtime. Using Docker, you can quickly deploy and scale applications into any environment and know your code will run.

The beauty of Docker lies in its simplicity and speed. Docker containers are lightweight because they use shared operating systems. This makes them much more efficient than virtual machines. You can create a Docker container in seconds, as opposed to the minutes it might take to create a virtual machine.

• Portability: Once you’ve created a Docker container, you can run it on any other system that has Docker installed. This eliminates the ‘it works on my machine’ problem.

• Scalability: Docker allows you to quickly scale up or down, depending on your needs. This is particularly useful in a microservices architecture.

• CI/CD Integration: Docker fits well into continuous integration/continuous deployment (CI/CD) workflows. You can create a container for each build, ensuring consistency across your development, testing, and production environments.

• Isolation: Each Docker container runs in isolation from others. This means that if one application crashes, it doesn’t affect the others.

Docker has revolutionized the way we develop, package, and deploy software. Its benefits of portability, scalability, CI/CD integration, and isolation have made it a favourite among developers and companies.

Docker’s practicality can be best understood through real-world examples. Let’s consider a few scenarios:

1. Simplifying Configuration: Imagine you’re developing an application that requires a specific version of Node.js. Instead of manually installing and configuring Node.js on your local machine, you can use a Docker image that already has Node.js set up. This not only simplifies your setup process but also ensures that your application will run the same way in different environments.

docker run -it --rm -v ${PWD}:/usr/src/app -w /usr/src/app node:14 node your-app.js

2. Microservices: Consider a large application that has been broken down into microservices. Each microservice can be packaged into a Docker container, with its dependencies. Docker’s isolation and scalability features make it perfect for managing microservices.

3. Continuous Integration/Continuous Deployment (CI/CD): In a CI/CD pipeline, consistency across different stages is crucial. With Docker, you can ensure that the application runs the same way in development, testing, and production. Here’s an example of how you might use Docker in a CI/CD pipeline:

# Build your app with docker
docker build -t my-app .

# Run tests in an isolated container
docker run my-app run-tests

# If tests pass, deploy the same container to production
docker tag my-app my-registry/my-app:latest
docker push my-registry/my-app:latest

These examples illustrate how Docker can simplify development, manage microservices, and maintain consistency in CI/CD pipelines.

Tasks

• Use the docker run command to start a new container and interact with it through the command line.

docker run -d --name nginx-con nginx

• Use the docker inspect command to view detailed information about a container or image.

docker inspect nginx

• Use the docker port command to list the port mappings for a container.

docker port 6257ca71277e

• Use the docker stats command to view resource usage statistics for one or more containers.

docker stats 6257ca71277e

or

docker stats --no-stream 6257ca71277e

• Use the docker top command to view the processes running inside a container.

docker top 6257ca71277e

• Use the docker save command to save an image to a tar archive.

docker save -o image.tar two-tier-flask-app_backend

• Use the docker load command to load an image from a tar archive.

docker load -i image.tar

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