The document explains the fundamentals of containerization and Docker, emphasizing how containers package software into lightweight, standardized units compared to traditional virtual machines. It outlines Docker's architecture, including the roles of the Docker daemon, client, and API, as well as basic commands for container manipulation, such as running, stopping, and publishing containers. Additionally, it highlights Docker's popularity and functionality in software development and deployment.

1. Containerization and Docker
Megha Bansal

2. What is a Container?
Package Software into Standardized
Units for Development, Shipment and
Deployment

3. Comparing
Containers and
Virtual Machines
Containers and virtual machines have similar
resource isolation and allocation benefits, but
function differently because containers
virtualize the operating system instead of
hardware. Containers are more portable and
efficient.

4. CONTAINERS
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
VIRTUAL MACHINES
Virtual machines (VMs) are an abstraction
of physical hardware turning one server
into many servers. 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.
Technology
Behind VMs
and
Containers

5. An open-source
containerization platform that
allows you to containerize your
applications
According to the Stack Overflow
Developer Survey - 2020,
Docker is the
#1 most wanted platform
#2 most loved platform
#3 most popular platform

6. Underlying
Technology
• Docker is written in the Go
programming language and takes
advantage of several features of
the Linux kernel to deliver its
functionality. Docker uses a
technology called namespaces to
provide the isolated workspace
called the container. When you run
a container, Docker creates a set
of namespaces for that container.
• These namespaces provide a layer
of isolation. Each aspect of a
container runs in a separate
namespace and its access is
limited to that namespace.

7. Architecture of
Docker

8. The engine consists of three major components:
• Docker Daemon: The daemon (dockerd) is a process that
keeps running in the background and waits for commands from
the client. The daemon is capable of managing various Docker
objects.
• Docker Client: The client (docker) is a command-line interface
program mostly responsible for transporting commands issued
by users.
• REST API: The REST API acts as a bridge between the daemon
and the client. Any command issued using the client passes
through the API to finally reach the daemon.
According to the official docs,
"Docker uses a client-server architecture. The Docker client talks to
the Docker daemon, which does the heavy lifting of building,
running, and distributing your Docker containers".
You as a user will usually execute commands using the client
component. The client then use the REST API to reach out to the
long running daemon and get your work done.

9. The Full Picture
The events that occur when you execute the command are as follows:
• You execute docker run hello-world command where hello-world is the name of an image.
• Docker client reaches out to the daemon, tells it to get the hello-world image and run a container from
that.
• Docker daemon looks for the image within your local repository and realizes that it's not there, resulting in
the Unable to find image 'hello-world:latest' locally that's printed on your terminal.
• The daemon then reaches out to the default public registry which is Docker Hub and pulls in the latest copy
of the hello-world image, indicated by the latest: Pulling from library/hello-world line in your
terminal.
• Docker daemon then creates a new container from the freshly pulled image.
• Finally, Docker daemon runs the container created using the hello-world image outputting the wall of text
on your terminal.

10. • It's the default behavior of Docker daemon to look for images in the hub that are not present locally. But once an
image has been fetched, it'll stay in the local cache. So, if you execute the command again, you won't see the
following lines in the output:
• If there is a newer version of the image available on the public registry, the daemon will fetch the image again.
That :latest is a tag. Images usually have meaningful tags to indicate versions or builds.

11. Docker
Container
Manipulation
Basics
1) How to run a container?
docker run <image-name>
Prior to version 1.13, Docker had only the previously mentioned command
syntax.
Later on, the command-line was restructured to have the following syntax:
docker <object> <command> <options>
In this syntax:
• object indicates the type of Docker object you'll be manipulating. This
can be
a container, image, network or volume object.
• command indicates the task to be carried out by the daemon, that is
the run command.
• options can be any valid parameter that can override the default
behavior of
the command, like the --publish option for port mapping.

12. 2) How to publish a port?
Containers are isolated environments. Your host system doesn't know anything about what's going on inside a container.
Hence,
applications running inside a container remain inaccessible from the outside. To allow access from outside of a container,
you must
publish the appropriate port inside the container to a port on your local network. The common syntax for the --publish or -p
option is as follows:
--publish <host port>:<container port>
Now to access the application on your browser, visit http://127.0.0.1:8080
3) How to list Containers?
The container ls command can be used to list out containers that are currently running.
To do so execute following

13. 4) How to stop or kill a running Container?
docker container stop <container identifier>
Where container identifier can either be the id or the name of the container.
5) How to restart a Container?
When we say restart we mean two scenarios specifically. They are as follows:
• Restarting a container that has been previously stopped or killed.
• Rebooting a running container.
docker container start <container identifier>

14. USE CASE-
DOCKER
https://medium.com/analytics-
vidhya/task-1-github-jenkins-and-
docker-integration-d3b7c1d60bb6

15. REFERENCES
• https://cloud.google.com/containers
• https://www.docker.com/resources/what-container
• https://www.freecodecamp.org/news/the-docker-handbook/
• https://docs.docker.com/get-started/overview/

16. Thank You!