Docker in a nutshell

Building and deploying new applications is faster with containers. Docker containers wrap up software and its dependencies into a standardized unit for software development that includes everything it needs to run: code, runtime, system tools and libraries. This guarantees that your application will always run the same and makes collaboration as simple as sharing a container image.

Images

• An image is a template (snapshot / blueprint) with instructions for creating the environment you want

• An image is immutable

• An image can be saved (pushed) into a registry (docker hub)

• To create your own image, you create a Dockerfile defining the steps needed to create the image and build it

Containers

• A container is a runnable instance of an image

• Images can be run on any machine with a docker daemon installed (portability) as containers if they have been build for the underlying platform / architecture

• Multiple containers can be created based on the same image

• Containers allow you to run an application in an isolated environment

• Many containers can be run simultaneously on a given host

• Containers run directly on the host machine’s kernel

Why docker - Containerization?

• Why developers care

  • A clean, safe, hygienic and portable runtime environment

  • No worries about missing dependencies, packages, and other pain points.

  • Run each app in its own isolated container, so you can run various versions of libraries and other containers

  • You can revert to “older” versions like a snap

  • Automate testing, integration and packaging

  • Recyclable environment(s)

  • Reduce / eliminate concerns about compatibility on other platforms

  • Handy tool to have even without the above, just for developers (local development)

• Why Ops care

  • Make the entire lifecycle more efficient, consistent, and repeatable

  • Increase the quality of code produced by developers

  • Eliminate inconsistencies between DTAP environments

  • Promote separation of concerns

  • Fallback to “working” version very easy

  • Significantly increase the speed and reliability for Continues Deployment and Integration

• Why not VM

  • Speed of deployment

  • Portability

  • Density & Performance

  • Cost

  • Size

  • Less host machine resources used

Extra information

• You can read much more about it in the Docker overview on the docker website.

• Virtual Machines vs. Docker Containers

Let’s quickly start playing with the Docker CLI next…