Docker Containter

 

1 What & why is Docker?............................................................................................................. 2

1.1 RAM - Memory.................................................................................................................... 2

1.2 Size & Startup...................................................................................................................... 2

1.3 Integration........................................................................................................................... 3

1.4 Docker Engine...................................................................................................................... 3

1.4.1 Docker Image................................................................................................................ 4

1.4.2 Docker container.......................................................................................................... 5

1.4.3 Docker registry............................................................................................................. 5

1.5 Docker Architecture............................................................................................................ 5

2 Docker tutorial........................................................................................................................... 6

2.1 Pull/Run/Stop/delete Docker Hello world....................................................................... 6

2.2 Run first Alpine Linux container........................................................................................ 7

2.3 Run Webapps with Docker................................................................................................. 8

3 Build Docker Image with Dockerfile......................................................................................... 9

3.1 What is Dockerfile............................................................................................................... 9

3.2 Dockerfile Basic commands............................................................................................... 9

3.2.1 Create Python-Flask-Webapps image with Dockerfile........................................... 10

3.2.2 Push your Docker mage to Docker cloud................................................................ 13

4 Reference.................................................................................................................................. 14

 

1 What & why is Docker?

Docker is software that offers a set of platform-as-a-service products for developing and deploying applications by packaging software in containers.

Container is lightweight, portable, virtual environments that developers can share without risking inconsistencies in development. Many organization are switching from using virtual machine to Docker containers.

1.1 RAM - Memory

Docker using less memory than virtual machine as there is no need to run guest OS.

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1.2 Size & Startup

Docker start-up faster as there is no need to load and run guest OS.

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1.3 Integration

Docker make it easier for developer to focus on coding rather than guest OS.

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1.4 Docker Engine

Docker engine is the application that is installed on host machine. It works like client-server application:

- A server which is a type of long-running program called a daemon process.

- A command line interface (CLI) client.
- REST API is used for communication between the CLI client and Docker Daemon.
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1.4.1 Docker Image

Docker Image is a template which is used to create docker containers. They are building block of docker container.

Docker let people create and share software through docker image, and we don't need to worry about compatibility, the docker container can alway run it.

The docker Image is create using build command.

the read only templates is used for creating container by using the run command.

We can either use a ready-made docker image from docker-hub or create a new image as per requirement.

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1.4.2 Docker container

Docker container is a ready application created from Docker Image, or we can say it is running instances of the Image and they hold the entire package needed to run the application.
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1.4.3 Docker registry

Docker registry is where the Docker Image is stored, the registry can be our local computer, or public repository like Docker Hub where multiple users can collaborate in building an application.

Docker Hub allow multple team within a organization to upload, share, and exchange Docker Image.

1.5 Docker Architecture

Docker Architecture: include 4 components

1) Docker client: user can use CLI to trigger Docker command.

2) Docker Host: run the Docker Daemon.

3) Docker Registry: storing Docker Images.

4) Docker Doemon: running inside Docker Host and responsible for images and containers.

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Docker Lifecycle:

1) Client use CLI to issue a command (Build/Pull/Run) to Docker Daemon.

2) Docker Daemon build an image based on your CLI command and save it to Registry (which can be locally or at Docker hub).

3) If Client donot want to build an Image, they pull it from Docker hub, which was built by another user.

4) Client can create a running instance of the Docker Image by issue a run command from the CLI, which will create a new running container.

2 Docker tutorial

2.1 Pull/Run/Stop/delete Docker Hello world

Pull the Docker Image hello-world from Docker hub:

$ docker pull hello-world

List all the docker images in your computer:

$ docker images

Run the Docker hello-world:

$ docker run hello-world

>> Hello world from Docker!

stop all docker container:

$ docker container prune

remove docker image:

$ docker image rm hello-world -f

2.2 Run first Alpine Linux container

Pull alpine image

$ docker pull alpine

Run alpine container from docker image

$ docker run alpine

Run linux command list folder command "Ls -s" inside docker

$ docker run alpine ls -l

Run echo "hello from alpine" command inside container

$ docker run alpine echo "hello from alpine"

List all currently running container

$ docker ps

List all the container command had ran in the past

$ docker ps -a

2.3 Run Webapps with Docker

Pull sample docker static site image

$ docker pull sample

Run docker sample site

docker run dockersamples/static-site

The webapp is running, but we cannot access it because there is no port to access the webapp from the browser, so let stop the container and configure the port

look up the container that is currently running: and get the ID of container

$ docker ps

then kill the container by the ID

$ docker stop ID

delete the container by the ID

$ docker rm ID

now, let run the container in detached mode

$ docker run --name static-site -e AUTHOR="Your Name" -d -P dockersamples/static-site

-d: will create a container with the process detached from your terminal

-p: will publish all the exposed container ports to random ports on the Docker host

-e: is how you pass environment variables to the container

--name: allows you to specify a container name

AUTHOR: is the environment variable name and Your Name is the value that you can pass

check the docker port command:

$ docker port static-site

443/tcp -> 0.0.0.0:49153

80/tcp -> 0.0.0.0:49154

the site should be available at: http://localhost:49154/

3 Build Docker Image with Dockerfile

3.1 What is Dockerfile

Dockerfile is a simple text file with a set of command or instruction to create a docker image, we can use dockerfile to create a new docker image when the existing docker images won't meet our requirement.
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Step to create and run new docker container:

1) create a dockerfile contain instruction to create a new docker image.

2) Run docker command to build new docker image

3) Run "docker run" command to create and run new container from docker image.

3.2 Dockerfile Basic commands

FROM Defines the base image to use and start the build process.

RUN It takes the command and its arguments to run it from the image.

CMD Similar function as a RUN command, but it gets executed only after the container is instantiated.

ENTRYPOINT It targets your default application in the image when the container is created.

ADD It copies the files from source to destination (inside the container).

ENV Sets environment variables.

3.2.1 Create Python-Flask-Webapps image with Dockerfile

1) pull a ubuntu:12.04

docker pull ubuntu:12.04

2) Create app.py

from flask import Flask, render_template

import random

app = Flask(__name__)

# list of cat images

images = [

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr05/15/9/anigif_enhanced-buzz-26388-1381844103-11.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr01/15/9/anigif_enhanced-buzz-31540-1381844535-8.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr05/15/9/anigif_enhanced-buzz-26390-1381844163-18.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr06/15/10/anigif_enhanced-buzz-1376-1381846217-0.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr03/15/9/anigif_enhanced-buzz-3391-1381844336-26.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr06/15/10/anigif_enhanced-buzz-29111-1381845968-0.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr03/15/9/anigif_enhanced-buzz-3409-1381844582-13.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr02/15/9/anigif_enhanced-buzz-19667-1381844937-10.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr05/15/9/anigif_enhanced-buzz-26358-1381845043-13.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr06/15/9/anigif_enhanced-buzz-18774-1381844645-6.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr06/15/9/anigif_enhanced-buzz-25158-1381844793-0.gif",

"http://img.buzzfeed.com/buzzfeed-static/static/2013-10/enhanced/webdr03/15/10/anigif_enhanced-buzz-11980-1381846269-1.gif"

]

@app.route('/')

def index():

url = random.choice(images)

return render_template('index.html', url=url)

if __name__ == "__main__":

app.run(host="0.0.0.0")

3) Create requirements.txt

Flask==0.10.1

4) Create templates/index.html

<html>

<head>

<style type="text/css">

body {

background: black;

color: white;

}

div.container {

max-width: 500px;

margin: 100px auto;

border: 20px solid white;

padding: 10px;

text-align: center;

}

h4 {

text-transform: uppercase;

}

</style>

</head>

<body>

<div class="container">

<h4>Cat Gif of the day</h4>

<img src="{{url}}" />

<p><small>Courtesy: <a href="http://www.buzzfeed.com/copyranter/the-best-cat-gif-post-in-the-history-of-cat-gifs">Buzzfeed</a></small></p>

</div>

</body>

</html>

4) Create Dockerfile

# our base image

FROM alpine:3.5

# Install python and pip

RUN apk add --update py2-pip

# install Python modules needed by the Python app

COPY requirements.txt /usr/src/app/

RUN pip install --no-cache-dir -r /usr/src/app/requirements.txt

# copy files required for the app to run

COPY app.py /usr/src/app/

COPY templates/index.html /usr/src/app/templates/

# tell the port number the container should expose

EXPOSE 5000

# run the application

CMD ["python", "/usr/src/app/app.py"]

5) build Docker myfirstapp by run docker build cmd:

$ docker build -t myfirstapp .

6) Run docker image myfirstapp just got built by dockerfile

$ docker run -p 8888:5000 myfirstapp

7) open browser at: http://localhost:8888/

3.2.2 Push your Docker mage to Docker cloud

1) login your docker account from cmd:

docker login

2) push docker image to cloud

docker push YOUR_USERNAME/myfirstapp

3) stop and remove docker image off your local computer:

$ docker stop myfirstapp

$ docker rm myfirstapp

4 Reference

https://www.edureka.co/blog/what-is-docker-container
https://geekflare.com/dockerfile-tutorial/
https://www.docker.com/resources/what-container
https://docs.docker.com/engine/reference/commandline/container/