Docker architecture (version modified)

Presentation By:
Mohammadreza Amini
Amir Arsalan
Autumn 2015
IRAN OpenStack Users Group
Docker Architecture
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Agenda
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| Iran Community OpenStack.ir
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Docker Concept
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How Does Docker Work?
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Should know about Docker
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Docker vs VMs
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Docker vs lxc
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The underlying technology

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Docker Concept

Docker is composed of following four components
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Docker Client and Daemon
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Images
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registries
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Containers

Docker Client and Daemon
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Docker Daemon
the Docker daemon runs on a host machine. The user does not directly interact
with the daemon, but instead through the Docker client.
Docker Client
The Docker client, in the form of the docker binary, is the primary user interface to
Docker. It accepts commands from the user and communicates back and forth with
a Docker daemon.

Images
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A Docker image is a read-only template.
Image type:
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Images that exist on register (docker hub)
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Images that can created with build

Registeries
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Docker registries hold images. These are public or private stores from which you upload or
download images. The public Docker registry is provided with the Docker Hub.

Containers
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Docker containers are similar to a directory. A Docker container holds everything that is
needed for an application to run. Each container is created from a Docker image.

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How Does Docker Work?

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Reference: https://docs.docker.com/article-img/architecture.svg

What happens when you run a container?
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Pulls the image
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Creates a new container
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Allocates a filesystem and mounts a read-write layer
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Allocates a network / bridge interface
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Sets up an IP address
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Executes a process that you specify
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Captures and provides application output

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Should know about Docker

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Docker is not LXC
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Docker is not a Virtual machine Solution.
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Docker is not a configuration management system and is not a replacement for chef,
puppet, Ansible etc.
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Docker is not a platform as a service technology.
Things you should know about Docker:

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Docker vs VMs

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Reference: https://risingstack-blog.s3-eu-west-1.amazonaws.com/2015/05/hypervisor-based-virtualization.jpg

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Reference: https://risingstack-blog.s3-eu-west-1.amazonaws.com/2015/05/os-virtualization.jpg

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Docker vs lxc

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Reference: https://www.flockport.com/lxc-vs-docker/

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The underlying technology

Namespaces
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Namespaces provides a layer of isolation: each aspect of a container runs in its own
namespace and does not have access outside it.
More Details: http://www.toptal.com/linux/separation-anxiety-isolating-your-system-with-linux-namespaces

Control Groups
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Cgroups running applications in isolation is to have them only use the resources you want. This ensures
containers are good multi-tenant citizens on a host. Control groups allow Docker to share available
hardware resources to containers and, if required, set up limits and constraints. For example, limiting the
memory available to a specific container.
More Details: https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

Union File System
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Union file systems, or UnionFS, are file systems that operate by creating layers, making them very
lightweight and fast. Docker uses union file systems to provide the building blocks for containers.
More Details: http://www.fsl.cs.sunysb.edu/docs/unionfs-tr/unionfs.pdf

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Any Question?

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Stay in Touch and Join Us:
● Home Page: OpenStack.ir
● Meetup age: Meetup.com/IranOpenStack
● Mailing List: OpenStackir@Lists.OpenStack.org
● Twitter: @OpenStackIR , #OpenStackIRAN
● IRC Channel on FreeNode: #OpenStack-ir

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Mohammadreza Amini
Linux Administrator
Mohammadreza@openstack.ir
Amir Arsalan
Python Developer
Arsalan@openstack.ir
Thank You

Docker architecture (version modified)

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