====== Docker ======
 
===== Release / History =====
[[https://www.docker.com/|{{ https://upload.wikimedia.org/wikipedia/commons/7/79/Docker_%28container_engine%29_logo.png}}]]
  * License: Apache 2.0
  * Started by Solomon Hykes at dotCloud
    * Jeff Lindsay independent collaborator
  * Released as open source in March 2013
  * In the years 2013 – 2016 many organizations started to support Docker
    * Cisco, Google, Huawei, IBM, Microsoft, and Red Hat
  * October 2015, the project had over 25,600 GitHub stars


Source: [[https://de.wikipedia.org/wiki/Docker_(Software)]]
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Picture Source:
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[[https://commons.wikimedia.org/wiki/File:Docker_(container_engine)_logo.svg]]

===== Architectural Facts =====
LXC -> libcontainer

  * Operating System Level Virtualization (no Hypervisor)
    * based on Linux Containers (LXC)
    * March 2014, with release version 0.9 Docker dropped LXC
  * Development of “libcontainer” started
    * cross-system abstraction layer
    * Docker execution environment
    * builds up a new container specification
    * wraps control-groups, namespaces and UnionFS
  * Similar implementations
    * rkt, FreeBSD Jail, OpenVZ, system-nspawn

{{https://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Docker-linux-interfaces.svg/400px-Docker-linux-interfaces.svg.png}}

Picture License: Public Domain 
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[[https://commons.wikimedia.org/wiki/File:Docker-linux-interfaces.svg#/media/File:Docker-linux-interfaces.svg]]


===== Deployment Facts =====
OS manages everything
  * a container is an isolation by defining limits through kernel features
    * Namespaces
      * process ids, hostnames, user ids and network access isolation
    * cgroups
      * Resource Management/-Limiting, CPU, memory, disk I/O, network
  * Docker introduces copy-on-write storage to manage images and containers
  * Docker aims to simplify and abstract this kernel level operations
  * a container feels like a VM but exists only due to an isolation mechanism provided by the OS

{{:en:dev:env:dockercontainer1.jpg?400|}}
===== Components 1 =====
Docker as an abstraction layer

  * Software
    * Docker daemon
      * listens to requests sent via Docker-Engine-API (REST)
    * Docker client
      * uses Docker-Engine-API
  * Objects
      * Images
      * Containers
      * Services
  * Registries
      * Hub
      * Sharing Images
      * Public: Docker Hub, Docker Cloud
  * Platform independent Container Specification

{{:en:dev:env:dockerlayers.jpg?400|}}
===== Components 2 =====
Docker Images and Containers

  * Images
    * built up from a series of layers
    * each represents an instruction in a dockerfile or may be a manual configuration
    * layers are read only, except the last one
  * Container
    * a read write layer
    * to be able to modify data which was read in an image layer, a copy-on-write process must be performed
    * copy-on-write copies a file from an image layer to the container layer before the system can modify it
    * all modifications may only be done on container layer
  * Flexible and Fast
    * it is possible to start multiple containers of the same kind quickly
    * versioning is easy to implement

{{:en:dev:env:dockercontainerlayer.jpg?400|}}
===== Components 3 =====
Docker Volumes

  * Volumes
    * define a volume which will be available in a container as folder
    * managed by Docker daemon on host
    * enables a sharing mechanism between containers
    * flexible, as directly managed by Docker and thus platform independent
    * remotely available
    * may be started pre-populated in a container, to avoid copy-on-write
  * Bind Mounts
    * directly mount a host folder into a container
    * not managed by Docker, not platform independent
  * Tmpfs mounts
    * temporary and only in memory
    * useful for sensitive data
    * no sharing, only on linux

{{:en:dev:env:dockervolumes.jpg?400|}}
===== Components 4 =====
Registry and Services

  * Registries enable sharing of images
    * push images to a registry to start sharing
    * pull images, to start from
    * thousands of apps available, each in an single image
    * different application versions, pre-configured in images
  * Public Registries
    * Docker Hub, Docker Cloud
  * Services
    * Scale containers across Docker daemons, swarm

===== Tools =====
Used to interact with Docker daemon

  * Docker-Toolbox
    * works on Windows and Mac
    * needs a virtualization driver to load a boot2docker iso
      * Virtualbox
      * Hyper-V
    * provides Docker-machine command to remotely interact with the Docker host, which is running in a VM
  * DockerCLI
    * provides commands to interact with the daemon, interacts mostly over Docker-Engine-API
  * Docker-Compose
    * runs multi-container Docker applications
    * configure a landscape using a YAML file
    * define ports, networks, volumes, environment variables, start order, dependencies 
  * Kubernetes
    * Container Orchestration
    * automated deployment, scaling, and management


Sources:

[[https://docs.docker.com/engine/docker-overview/]]
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[[https://docs.docker.com/engine/reference/commandline/dockerd/#daemon-socket-option]]
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[[https://docs.docker.com/storage/storagedriver/#images-and-layers]]
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[[https://docs.docker.com/compose/overview/]]
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[[https://docs.docker.com/machine/]]
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[[https://en.wikipedia.org/wiki/Docker_(software)]]
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[[http://jancorg.github.io/blog/2015/01/03/libcontainer-overview/]]
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[[https://github.com/docker/libcontainer/blob/4940cee052ece5a8b2ea477699e7bb232de1e1f8/SPEC.md]]
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[[https://www.infoq.com/news/2013/03/Docker]]
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[[https://github.com/torvalds/linux]]
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