Docker Introduction

Docker Introduction

• Docker is an Open Source Platform designed to build, distribute and run applications inside the container.
• Docker is Virtual box that packages applications.
• Docker implements a high level API to proceed the light weight containers that run processors.
• Also Docker is a tool for "Rapid Application Development"
• Docker will use in Dev, Testing, Stage but before will not use in production because of security reason.
• But now Docker itself has clearances, They integrated with SE-Linux(know that is for Security purpose).

Virtual Machines Vs Containers

                            VM's                                                          Docker Containers
   

                 -> More time to Create                               -> Less time to create

                 -> Dedicated OS                                        -> Common OS

                 -> Specific bin/lib                                       -> Common bin/lib

                 -> Dedicated Resources                              -> Common resources

                 -> Memory wastage                                    -> No Memory Wastage

                 -> Low Performance                                   -> high performance

                 -> Complex Configure                                -> Simple Configuration

                 -> Heavy Weight (Gb's)                              -> Light Memory (Mb's)

                 -> Memory can not share                             -> Can Share Memory

Docker Core Terminology

Docker mainly have Core parts. Those are

                   ** Images
                   ** Containers
                   ** Dockerfile
                   ** Docker Volumes
                   ** Docker Compose
                   ** Docker Network

Docker Images: 

• Docker image is a collection of files and source meta data.
• Images are made of layers, Conceptually stacked on top of each other.
• Images can share layers to optimize the disk usage, transfer times and memory usage.
• Docker image is Read Only file system.

Docker Containers:

• A container is an executable form of docker image.
• A Container is an encapsulated set of processes running in read-write copy of the file system.

Dockerfile:

• Creates images automatically by using a build script: <Dockerfile>
• Can be versionized in a version control system like Git or SVN along with all dependencies.
• Docker hub can automatically build images based on dockerfiles on GitHub.

Docker Volumes:

• In Docker, we have a separate volume that can shared across containers. These are known as Data Volumes.
• They are initialized when the container is created.
• They can be shared and also reused among many containers.
• Any changes to the volume itself can be made directly.
• They exist even after the container is deleted.

          Ex: # docker run -it -v /root/files:/files ubuntu

Docker Compose:

• Docker Compose is a tool for defining and running multi-container Docker applications.
• With Compose, we use a compose file to configure application's services.
• Then, by using a single command we can create and start all the services from the given configuration requirement.

Docker Network: 

• To communicate Docker Containers with each other and the outside world via the host machine, there has to be a layer of networking involved.
• Docker supports different types of networks, each fit for certain use cases.
• Different Network Types    

       Docker comes with network drivers geared towards different use cases. The most common network types being:

• Bridge
• Overlay
• Macvlan

Run Platforms:

• Various Linux Distributions (Ubuntu, CentOS, Fedora, RHEL, OpenSUSE, ...)
• Cloud (AWS, GCP, Rackspace)
• 2014-10: Microsoft announces plans to integrate Docker with next release of Windows Server.
• 2013-03: Releases as Open Source Tool.