Estimated reading time: 15 minutes
Why use Docker
Docker allows for the rapid creation and management of self contained computer environments. These self contained environments, or containers, simplify software development, server management, and deployment. Docker allows system users to build configurations quickly and to run them on any Docker compatible system.
Key Docker concepts
Docker is a platform that helps develop, deploy, and run applications inside of Linux containers. Using Linux containers to deploy applications is called containerization. While containers are not new, their ease of use when deploying applications is.
Containers are increasingly popular because of their:
- Lightness: Containers leverage and share host resources.
- Flexibility: Even the most complex applications can be containerized.
- Swap-ability: You can deploy updates and upgrades on-the-fly.
- Portability: You can build locally, deploy to the cloud, and run containers anywhere.
Images and containers
An image is an executable package that includes everything needed to run an application: code, runtime libraries, environment variables, and configuration files. Images are built, then containers are launched by running images.
A container is a runtime instance of an image. It is what runs in memory when the image is executed. You can see a list of your running containers with the command
Containers and virtual machines
Containers run natively in Linux and share the valuable resources of the host machine with other containers. They run as discrete processes, making them lightweight, taking no more memory than other applications. On the other hand, virtual machines (VMs) run full-blown “guest” operating systems - each needing access to valuable host resources.
TODO Container stack example Virtual machine stack example (image)
1. Install Docker.
Docker can be installed on almost any desktop or laptop computer, as well as on most servers and specialty computers like the Rasberry Pi. It's best to install a copy of Docker locally. If you're working on a tablet, phone, or Chromebook instead follow the Docker in your own Cloud tutorial.
After finishing your istallation, add your user account to the
docker group. Read more.
2. Test Docker version
docker --versionto ensure that you have a supported version of Docker:
docker --version Docker version 17.12.0-ce, build c97c6d6
docker infoor (
--) to view more details about your docker installation:
docker info Containers: 0 Running: 0 Paused: 0 Stopped: 0 Images: 0 Server Version: 17.12.0-ce Storage Driver: overlay2 ...
3. Test Docker installation
- Test that your installation works by running the simple Docker image - hello-world:
docker run hello-world Unable to find image 'hello-world:latest' locally latest: Pulling from library/hello-world ca4f61b1923c: Pull complete Digest: sha256:ca0eeb6fb05351dfc8759c20733c91def84cb8007aa89a5bf606bc8b315b9fc7 Status: Downloaded newer image for hello-world:latest Hello from Docker! This message shows that your installation appears to be working correctly. ...
- List the
hello-worldimage that was downloaded to your machine:
docker image ls
- List the
hello-worldcontainer (spawned by the image) which exits after displaying its message. If the container was still running, you would not need the
docker container ls --all CONTAINER ID IMAGE COMMAND CREATED STATUS 54f4984ed6a8 hello-world "/hello" 20 seconds ago Exited (0) 19 seconds ago
## List Docker CLI commands docker docker container --help ## Display Docker version and info docker --version docker version docker info ## Execute Docker image docker run hello-world ## List Docker images docker image ls ## List Docker containers (running, all, all in quiet mode) docker container ls docker container ls --all docker container ls -aq
Conclusion of part one
Containerization makes development and deployment seamless. For example Docker containerized:
- applications have no external system dependencies
- updates can be pushed quickly to any part of a distributed application
- resource density can be optimized
Using Docker scaling your application is a matter of spinning up new executables, not configuring and running heavy Virtual Machines.