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Docker Concept & Setup

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Why Containerization ?

Up to now we have been working with monolithic applications where different components of service are packaged into a single application which is easy to develop, test and deploy.But when it becomes large and complex it’s become difficult as one team to work on it and the risk of failure is high at deploy time.
So to overcome, a new trend has been followed to work with microservices where components of the monolithic application are divided into small microservices. Here every microsevice will have its own API to handle its part of the application.

Virtual Machines are too big to transfer and often too slow.

So containerization is the better choice when adopting Microservices architecture.

Container ???

 

Docker ??

Docker is one of the most popular container product, that is based on LXC and  is an open platform to build , ship and run distributed applications.

 

  –   Docker Engine : portable, lightweight runtime packaging tool
   –  Docker Hub: A cloud service for sharing application

Docker images are built from Dockerfile and the containers are built from images.

:: Setup ::

Installing Docker is easy. All the commands used here are in OEL6 in my workplace.

1. Installation:

Update OS to atleast OEL6_UEK4 repo to use kernel > 4.1 (yum update and confirm kernel version, os > 6.4)
[ol6_UEKR4]
name=Latest Unbreakable Enterprise Kernel Release 4 for company Linux $releasever ($basearch)
baseurl=http://public-yum.company.com/repo/companyLinux/OL6/UEKR4/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-company
gpgcheck=1
enabled=1

yum update and reboot

> use docker repo:

[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/companylinux/6
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg

2. Use btrfs filesystem:

yum install btrfs-progs
mkfs.btrfs /dev/sdb ( Add a raw disk and format with brtfs )
(FS tab entry )/dev/sdb /var/lib/docker btrfs defaults 0 0

3. Add proxy (if any to contact docker HUB)

/etc/sysconfig/docker ( If any ) OR add in /etc/default/docker( to use it with CURL)

export HTTP_PROXY=”proxy_URL:port”
export HTTPS_PROXY=”proxy_URL:port”

4. Modify docker config

In /etc/init.d/docker

Update

“$unshare” -m — $exec -d $other_args &>> $logfile &

to

$exec -d $other_args &>> $logfile &

5. Start docker service

# service docker start
# chkconfig docker on

6. Check docker details

service docker status
docker info
docker version

7. Add local user to docker group

groupadd docker
usermod -a -G docker <local docker>
chmod g+rx /var/lob/docker

8. Search images in docker hub:(Before pulling check the availability)

docker search oraclelinux
docker searcg centos
docker searcg registry

9. pull oracle linux6.6 image:

docker pull oraclelinux:6.6

here oraclelinux – image is 6.6 – version

10. Check images:

docker images

11. Add this env variable for authenticity, integrity of images

export DOCKER_CONTENT_TRUST=1

 


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