Software Engineering 2

4 Prozesse und Werkzeuge,

Docker Container

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Docker is a popular software packaging, distribution and execution infrastructure using containers (Overview):

• Docker runs on Linux only (LXC). MacOS and Windows have developed adapter technologies.

• Windows uses an internal Linux VM to run the Docker engine (or the Docker daemon process: dockerd ).

• Client tools (CLI, GUI, e.g. Docker Desktop) are used to create, manage and execute containers.

First introduction (2013): Salomon Hykes at PyCon 2013, Santa Clara CA: "The Future of Linux Containers" (video, 5:21min).

Docker builds on Linux technologies:

• Stackable layers of filesystem images that each contain only the changes to an underlying image.

• Tools to build, manage and distribute images ("ship container" metaphore).

• Linux LXC or similar technology is used to "run containers" as groups of isolated processes on a Linux system.

Docker is used to:

• Aquire, deploy and use software (e.g. MySQL database) without installation on the host system.

• Package own software and "ship-as-a-container" rather than in proprietary formats that require installation in the target environment.

Packaging and distributing software as a container becomes part of the software build process.

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Docker core concepts:

• Image - compound of stacked images (image layers) starting with a base image that yields a final filesystem impression that is visible inside a container.

  • Each image layer can be created and distributed independently.
  • Each image is built by a Dockerfile.

• Registry - local or global repository to share images, e.g. Docker Hub.

• Container - Information (state) comprised of:

  • Id, name,
  • Reference to an image (top of image stack),
  • Entry point, arguments, environment variables,
  • Ports, mounted volumes, etc.

• Running Container instance - Process group executing on the state of a Container. Process groups of one container are fully isolated from state of other containers and the state of the host system.

• Orchestration of Container instances (docker-compose) - from sets of containers, e.g. a database container and an application container. Combine configuration and life cycle control in a single docker-compose.yaml file.

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Basic docker commands:

• Image lifecycle commands (lifecycle: states over creation, existence, removal):

  • docker build | rmi (rmi: remove image),
  • docker pull | push from/to a registry.

• Container lifecycle commands:

  • docker run | start | stop | rm (rm: remove container).
  • docker exec - attach processes to container.

• Inspection commands:

  • show images: docker images,
  • show containers: docker ps -a (existing and running containers -a),
  • show output: docker logs.

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Docker Overview:

 

Stackable images:

 

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Reference Documentation

For further reference, find information at links:

• Getting Docker (installation), here.
• Docker Reference, here.
  • Docker Commands, here, cheatsheet
  • Dockerfile cheatsheet.
• Docker Hub, link.
• Orchestration (docker-compose)
  • Compose Reference, here,
  • docker-compose cheatsheet.
• Docker Meetup Berlin, past events, upcoming.
• DockerCon'22, May 9-10, 2022, link, YouTube.
• Salomon Hykes at PyCon 2013, Santa Clara CA: "The Future of Linux Containers" (video, 5:21min).

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