Docker Introduction:

History of Docker:

Docker was released in 2013 by a hosting company called Dot Cloud (Company no longer exists)
It’s been 5 years since Docker was released and now it’s a revolution
Huge shift in infrastructure [Mainframe to PC, Bare metal to Virtualization, Data Center to Cloud, Containers]

Docker is an open source platform for developing, shipping, and running applications.
Docker is an open-source project that automates the deployment of applications inside software containers, by providing an additional layer of abstraction and automation of operating system-level virtualization on Linux
Docker packages an application and all its dependencies in a ‘virtual container’ so that it can be run on any Linux system or distribution
Docker enables you to separate your applications from your infrastructure so you can deliver software quickly.
Docker provides the ability to package and run an application in a loosely isolated environment called a container

Virtualization refers to the creation of a virtual resource such as a server, desktop, operating system, file, storage or network
Server virtualization uses a software layer called a HYPERVISOR to emulate the underlying hardware
Virtualization software allows you to set up one operating system within another

Hypervisor decouples the virtual machines from the host and dynamically allocates computing resources to each virtual machine

Virtual machines (VMs) are an abstraction of physical hardware turning one server into many servers
Virtual machines are emulation of a specific computer system type
The physical, "real-world" hardware running the VM is generally referred to as the 'HOST', and the virtual machine emulated on that machine is generally referred to as the 'GUEST'. A HOST can emulate several GUESTS, each of which can emulate different operating systems and hardware platforms
A virtual machine is isolated from the hardware and has to communicate with the hardware through a Hypervisor
The hypervisor allows multiple VMs to run on a single machine. Each VM includes a full copy of an operating system, the application, necessary binaries and libraries - taking up tens of GBs
VMs can also be slow to boot

Containers are an abstraction at the app layer that packages code and dependencies together
Multiple containers can run on the same machine and share the OS kernel with other containers, each running as isolated processes in user space
Containers take up less space than VMs (container images are typically tens of MBs in size), can handle more applications and require fewer VMs and Operating systems
Containers are light weight
Containers do not have their own kernel
Containers share the host machine’s kernel, making them much smaller in size compared to virtual machines
Containers use process level isolation, allowing processes inside a container to be isolated from other containers