Docker Docs

Docker notes, small projects, and solutions from several sources.

Table of Contents

• What is docker?
  • What is a container?
  • Before vs After Containers
  • Docker Image vs Container
• Docker vs Virtual Machine
• Most Common Commands

What is Docker?

What is a Container?

• A way to package application with all the necessary dependencies and configurations
• Portable artifact, easily shared and moved around
• Makes development and deployment more efficient.
• Layers of images
• Mostly Linux Base Image, bc small in size
• Application image on top

Containers live in container repositories:

• Private repositories
• Public repository for Docker (e.g: DockerHub)

Before vs After Containers

Before Containers

• Installation process different on each OS environment
• Many steps where something could go wrong
• Configuration on server needed: Dependency version conflicts
• Textual guide of deployment: Misunderstandings

After Containers

• Own isolated environment (based on lightweight linux)
• Packaged with all needed configuration
• One command to install the app
• Run same app with 2 different versions
• Developers and Operations work together to package the application in a container
• No environmental configuration needed on server (except Docker Runtime)

Docker Image vs Container:

• Image:
  • The actual package
  • Artifact, that can be moved around
• Container:
  • Actually start the application
  • Container environment is created

Docker vs Virtual Machine

The difference lies on what parts of the operating system they virtualize:

• Docker virtualizes the Applications layer
• Virtual Machines virtualizes the OS Kernel and the Applications layer

This means:

• Size: The size of Docker images are much smaller (couple of MB)
• Speed: Docker containers start and run much fast
• Compatibility: VM of any OS can run on any OS host -- Docker can't do this, a workaround is installing a technology called Docker Toolbox which abstracts away the Kernel

What is Docker?

Docker is a set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called containers. - Wikipedia

From the above definition, basically, Docker consists of three things:

1. A set of Platform as a Service (PaaS)
2. Docker uses OS-level virtualization
3. For delivery of software in packages called containers

Docker Architecture:

Most Common Commands

Command	Explanation	Shorthand
docker image ls	Lists all images	docker images
docker image rm [image]	Removes an image	docker rmi
docker image pull [image]	Pulls image from a docker registry	docker pull
docker container ls	Lists running containers	docker ps
docker container ls -a	Lists all containers	docker ps -a
docker container run [image]	Runs a container from an image	docker run [image]
docker container rm [container]	Removes a container	docker rm [container]
docker container stop [container]	Stops a container	docker stop [container]
docker container exec [container]	Executes a command inside the container	docker exec [container]

Sources

• DevOps with Docker
• Docker Training