A Deep Dive into Containerization

Application Containerization:

• OS-level virtualization , used to deploy and run application without launching entire VM for the respective app.
• Needs to ensure the application is tested in container before shipping to higher environment. Dependency and security, access might be different in the next envs.
• Wrap your code to lightweight container and pass it on to Ops team to deploy it to prod. 
• You can setup your own repository as needed.We can create image using current container as well.

Commands:

Docker pull : download image and put in your local m/c

Docker run:

Docker stop

Docker exec  -it <image_name>  /bin/bash   //Docker enter into the container 

Docker commit <image_name>  repo_name/image_name:some_tag

Docker login  default/<repo>

Docker push >  repo_name/image

From command is used to specific the base image/ reference branch on which we are going to create image. Further layer on top of it.

Sample File:

FROM ubuntu

//FROM  repo_name/<ubuntu_image_name>

// From google? Login to google repo: docker login url

RUN apt-get -y install apache2

Add <source_location> <destination>

Add .  var/www/html

CMD apachectl  -D FOREGROUND

ENTRYPOINT apachectl  -D FOREGROUND

COPY:

CMD is used to run on the start of the container. ‘apachectl  -D FOREGROUND ‘ Used to keep the container up and running.

ENTRYPOINT: can’t be override using argument

For eg. Docker exec -it <image_name> /bin/bash . Here /bin/bas is getting overridden using CMD

Every container will require a single process which should always keep on running at the container start. Apachectl command is going to be executed at the time of container start.

Put a script , ru a while loop using sleep command. Sleep command will make sure that conainer is always running. So pass on any command that keep the container up and running.

Sample2 - v1

Vim Dockerfile // when we run the build, it will always look for Dockerfile

FROM ubuntu:latest

RUN apt-get update

RUN apt-get install apache2

ADD index.html /var/www/html

ENTRYPOINT apachectl  -D FOREGROUND

ENV name DEVOPS

Each line adds a separate layer. Need to achieve the target with minimum number of run command.

Run command will be executed at the time of creating the image

Sample 2 - v2

FROM ubuntu:latest

RUN apt-get update && apt-get install apache2

ADD index.html /var/www/html

ENTRYPOINT apachectl  -D FOREGROUND

ENV name DEVOPS

ENV name =DEVOPS name1=hello-docker

Whenever there is a public stuff, while pulling login is not required, During push it does require.

Docker build -t <repo_name>/<image_name>:version_0.1 // create

Docker push <repo_name>/<image_name>:version_0.1

docker run >-d <image_name>

docker inspect container_id  . It runs on a private IP. Need to expose the container to the host m/c in order to access it.

docker run -p  host_mc__port_81: container_port_80 -d image_name.

docker  run -p 81:80 -p 82:8080

Ultimately we are going to hit host m/c not the container

External_ip:exposed_ip

Netstat  -tunlp

Docker rm image_name

EXPOSE