docker container overview

Docker Container OverviewMizan Rahman

CIS280: Running and Scaling Applications using Docker and Kubernetes

Outline

● Overview of Docker Container

● Running Hello World in Docker

● Running a Docker Container in Detached Mode

▪ Building a Docker Image with a Dockerfile

▪ Package an Application Inside a Container



Processes

Process Process ProcessProcess

code

Process

Process

Another

Computer

Another OSAnother OS

Another OSAnother OS

Another

Computer

Another

Computer

Another

Computer

Docker EngineDocker

Engine

Process

Exe

Docker

Image


Docker Container Key Conceptscode

System lib

System tools

Dockerfile

Settings

Docker

build

Docker

run

Docker

run

What is a Container?

• A container is a standard unit of software that packages

up code and all its dependencies, so the application runs

quickly and reliably from one computing environment to

another.

• A Docker container image is a lightweight, standalone,

executable package of software that includes everything

needed to run an application in user space:

▪ code,

▪ runtime,

▪ system tools,

▪ system libraries and

▪ settings.

https://www.docker.com/resources/what-container


https://www.docker.com/resources/what-container

Container Advantage

• Docker containers that run on Docker Engine:

• Standard: Docker created the industry standard for containers, so

they could be portable anywhere

• Lightweight: Containers share the machine’s OS system kernel

and therefore do not require an OS per application, driving higher

server efficiencies and reducing server and licensing costs

• Secure: Applications are safer in containers and Docker provides

the strongest default isolation capabilities in the industry



Docker architecture

Docker Hub (Image Repo)


• Please create a docker hub account if you do not have already.

• https://hub.docker.com/signup

https://hub.docker.com/signup

Running Hello World in Docker• docker run hello-world

• docker ps

• docker container ls

• docker container --help

• docker ps -a

• docker images

• (stored in:/var/lib/docker/image/overlay2/imaged/content)

• ls /var/lib/docker/image/overlay2/imagedb/content/sha256

• docker info

• (Docker root dir: /var/lib/docker)

• ls /var/lib/docker

• ls /var/lib/docker/containers

• docker logs hello-world

• docker inspect hello-world


Port Mapping (Host:Container)

Port

80

Port

8080

eth1 (192.168.1.25)

Nginx Container

http.server Bridge

CentOS VM

Windows /Mac/linux host OS (192.168.1.20)

docker run -p 8080:80


Running a Docker Container in

Detached Mode• docker run -d -p 8080:80 --name nginxcontainer nginx

• #Open in the browser http://192.168.1.25:8080/ (eth1 ip addr of MasterVM)

• docker ps

• # Get to bash (Bourne Again Shell)

• docker exec -it nginxcontainer /bin/bash

• Or you can Get to the sh (Bourne shell)

docker exec -it nginxcontainer /bin/sh

• ls

• pwd

• cat /usr/share/nginx/html/index.html

• exit

• docker ps

• docker stop nginxcontainer

• docker rm nginxcontainer

-d : Detached, Run container in the background

-a=[] : Attach to `STDIN`, `STDOUT`, `STDERR`

-t : Allocate a pseudo-tty (TeleTYpewriter)

-i : Keep STDIN open even if not attached

-p : Publish a container’s port(s) to the host

-m : Memory limit


http://192.168.1.25:8080/

Building a Docker Image with a Dockerfile

• Create the following text file named Dockerfile in an empty working

directory:

• mkdir hello-app

• cd hello-app

• vi Dockerfile

FROM alpine

CMD echo Hello CIS280 !

• docker build -t hello-app . # Provide a name and tag

• docker images #This will get the image id

• docker run hello-app # Start and run the container

• docker ps -a # Container exited as it is finished it purpose

• docker rm hello-app # Removed the stopped container

• docker container prune # Delete any stopped container


Package an Application Inside a Container

#Package an Application Inside a Container

#crate a index.html for a webserver.

cd ..

mkdir webserver

cd webserver

echo "<html><h1>Hello CIS280</h1></html>" > index.html

vi Dockerfile

#copy following in to the Dockerfile

FROM centos:latest

RUN yum -y install httpd

COPY index.html /var/www/html/

CMD ["usr/sbin/httpd", "-D", "FOREGROUND"]

EXPOSE 80

Build and Run the Application • #Build docker image

• docker build -t webserver:v1 .

• docker images

• docker run -d -p 8080:80 --name webserver webserver:v1

• #Open in the browser http://192.168.1.25:8080/ (eth1 ip addr of MasterVM)

• docker exec -it webserver /bin/bash

• cat /var/www/html/index.html

• #or incase image has issue you can run and get the to the container

• docker run -it webserver /bin/bash

• docker stop webserver

• docker rm webserver

• docker container prune

Dockerfile Commands• #Dockerfile Commands

• #Get base image (or From scratch)

• FROM centos:latest

• # Set the working directory.

• WORKDIR /var/www/html/

• #Get executed during the build of the image

• RUN yum -y install httpd

• #expose the containter port

• EXPOSE 80

• #copy local files into the container wroking directory

• COPY index.html .

• #executed inside the container

• CMD ["usr/sbin/httpd", "-D", "FOREGROUND"]

https://docs.docker.com/engine/reference/builder/

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/

https://docs.docker.com/engine/reference/builder/

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/

CIS280: Running and Scaling Applications

using Docker and Kubernetes

docker container overview

Documents