Docker Hands-on Repository

A collection of Hands-on Docker labs.
Each lab is a standalone lab and does not require to complete the previous labs.

Docker

Prior to Docker we had to use 3^rd party tools for virtualization
Docker relay on Linux Kernel 3.8.13 and above. This version added the required features for executing Docker at kernel level
Docker is based upon Linux Container

Containers use kernel cgroups.
A cgroup is a collection of processes that are bound to a set of limits or parameters defined via the cgroup filesystem.
Control groups, usually referred to as cgroups, are a Linux kernel feature which allow processes to be organized into hierarchical groups whose usage of various types of resources can then be limited and monitored. cgroups consist of one hierarchy (tree) per resource (cpu, memory, …)
The kernel's cgroup interface is provided through a pseudo-filesystem called cgroupfs.
Grouping is implemented in the core cgroup kernel code, while resource tracking and limits are implemented in a set of per-resource-type subsystems (memory, CPU, and so on).

Containers use kernel namespaces for isolation.
A namespace wraps a global system resource in an abstraction that makes it appear to the processes within the namespace that they have their own isolated instance of the global resource.
Changes to the global resource are visible to other processes that are members of the namespace, but are invisible to other processes.
namespace Allow you to create isolation of:
- Process trees (PID Namespace)
- Mounts (MNT namespace) wc -l /proc/mounts
- Network (Net namespace) ip addr
  - Isolation on the networking level is achieved through the creation of virtual switches in the linux kernel.
- Users / UIDs (User Namespace)
  - User namespaces isolate security-related identifiers and attributes, in particular, user IDs and group IDs
- Hostnames (UTS Namespace) hostname
- Inter Process Communication (IPC Namespace) ipcs

In the past Docker were based upon Linux containers (LXC).
LXC is a composition of cgroup & namespace for providing isolated environment which allow sandboxing processes from one another, and controlling their resource allocations.
LXC bundles with the kernel’s Cgroups to provide the functionality for the process and network space instead of creating a full virtual machine and provides an isolated environment for the applications.
With the release of version 0.9 Docker.io have dropped LXC as the default execution environment, replacing it with their own runc/libcontainer.
- Libcontainer provides a native Go implementation for creating containers with namespaces, cgroups, capabilities, and filesystem access controls. It allows you to manage the lifecycle of the container performing additional operations after the container is created
In July 2015 Docker moved to runc