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Docker Introduction

Docker

What is Docker?

Docker is a computer program that performs operating-system-level virtualization, also known as “containerization”.

Docker

Simply its a toy box with all the toys you need to play with.

So what is containerization or container?

Containerization is a lightweight alternative to full machine virtualization that involves encapsulating an application in a container with its own operating environment.

Docker

So Suppose, for instance, that two apps both use Node but have various versions. In a solitary setting, they may run beside one another without interfering with one another.

so we can say that container is a isolated environment for running an application.

So Docker is a VM ?

Docker

No, Docker is not a VM. Docker is a containerization platform which packages your application and all its dependencies together in the form of containers so as to ensure that your application works seamlessly in any environment be it development or test or production.

What the difference between VM and Docker?

First, let's understand two terms:

  • kernel
  • Hypervisor

Kernel

A kernel is the central part of an operating system. It manages the operations of the computer and the hardware, most notably memory and CPU time.

its main job is to manage the communication between the software and the hardware.

Hypervisor or Virtual Machine Monitor (VMM)

A hypervisor is a program that allows multiple operating systems to share a single hardware host. Each operating system appears to have the host's processor, memory, and other resources all to itself.

So what is the difference between VM and Docker?

  • Docker is a containerization platform which packages your application and all its dependencies together in the form of containers so as to ensure that your application works seamlessly in any environment be it development or test or production.

container

  • A virtual machine (VM) is an operating system (OS) or an application that enables you to run multiple operating systems on the same physical hardware machine, and in a secure, isolated environment.

VM

A container runs natively on an OS and shares the kernel of the host machine with other containers. It runs a discrete process, taking no more memory than any other executable, making it lightweight.

By contrast, a virtual machine (VM) runs a full-blown “guest” operating system with virtual access to host resources through a hypervisor. In general, VMs incur a lot of overhead beyond what is being consumed by your application logic.

Containers Virtual Machines (VMs)
Technology Docker, Kubernetes, containerization platforms VMware, Hyper-V, Xen, virtualization platforms
Isolation Lightweight isolation Strong isolation
Resource Shares host OS kernel, minimal duplication Emulates complete OS, duplication of OS and system resources
Overhead Lower resource overhead, faster startup times Higher resource overhead, slower startup times
Portability Highly portable, easy to deploy across different hosts Less portable, tied to specific virtualization platform
Scalability Easy to scale horizontally and vertically Scaling depends on virtualization platform capabilities
Use Cases Microservices, distributed applications Legacy applications, different OS requirements
Performance Better performance due to reduced overhead Slightly reduced performance due to virtualization layers

Source: Docker vs. VMs

So why container is faster in booting up than VM?

Because docker container is just a process that runs on the host machine, so it doesn't need to boot up a whole OS.

While VM is a whole OS that runs on the host machine, so it needs to boot up the whole OS.

why creating a container is faster than creating a VM?

because we dont need hypervisor to create a container, while we need hypervisor to create a VM.

A Docker container, unlike a virtual machine, does not require or include a separate operating system. Instead, it relies on the kernel’s functionality and uses resource isolation for CPU and memory, and separate namespaces to isolate the application’s view of the operating system.

image

Docker Images

A Docker image is a file, comprised of multiple layers, that is used to execute code in a Docker container. An image is essentially built from the instructions for a complete and executable version of an application, which relies on the host OS kernel.

A Docker image is containing everything needed to run an application as a container. This includes:

  • code
  • runtime
  • libraries
  • environment variables
  • configuration files
  • The image can then be deployed to any Docker environment and executable as a container.