I heard about Docker when I was in Puppet Conf 2014. There has a session to talk about Docker and Puppet corporation. I know there has application visualization when I was doing VM image deduplication but was surprise it came out to the market early and turns out very popular. I would like to share the Docker Proof of Concept Lab I built base Ubuntu VM via VirtualBox. It actually shows how easy to make DevOps adopt CI/CI concept. Here, I list the major sections for my blog and hope you would enjoy it.
Outline
- 1. What's Docker.
- 2. Installation
- 3. Permission
- 4. Docker Commands
- 5. More Run Commands
- 6. Build Docker Image
1. What's Docker
Docker is an open-source that makes creating and managing Linux containers. Here is standard statement from Docker - Docker is an open platform for developers and sysadmins to build, ship, and run distributed applications. Consisting of Docker Engine, a portable, lightweight runtime and packaging tool, and Docker Hub, a cloud service for sharing applications and automating workflows, Docker enables apps to be quickly assembled from components and eliminates the friction between development, QA, and production environments. As a result, IT can ship faster and run the same app, unchanged, on laptops, data center VMs, and any cloud. I reference the docker explanation for the people has familiar VM already. I think it's easier to get you get the point !.
What's linux container ?
Containers are like extremely lightweight VM(Virtual Machines)s - they allow code to run in isolation from other containers but safely share the machine resources, all without the overhead of a hypervisor.
Linux Containers (LXC)
LXC combines "cgroups" and "namespace" support to provide an isolated environment for applications. Docker can also use LXC as one of its execution drivers, enabling image management and providing deployment services.
Docker Registry
DOCKER REGISTRY - REPOSITORIES OF DOCKER IMAGES - We need to have a disk image to make the virtualization work. The disk image represents the system we're running on. Docker registry is a registry of already existing images that we can use to run and create containerized applications.
Why setup via Ubuntu first ?
Ubuntu Trusty comes with a 3.13.0 Linux kernel, and a docker.io package which installs Docker 0.9.1 and all its prerequisites from Ubuntu's repository.
Ubuntu (and Debian) contain a much older KDE3/GNOME2 package called docker, so the package and the executable are called docker.io.
2. Installation
Generally, the way I try is follow the instruction (https://docs.docker.com/installation/ubuntulinux/), it downloads the package lists from the repositories and "updates" them to get information on the newest versions of packages and their dependencies by synchronizing the package index files fetched from /etc/apt/sources.list.
preparation
#sudo apt-get update
#sudo apt-get install docker.io
To make the shell easier to use, we need to create a soft link since /usr/local/bin is for normal user programs not managed by the distribution package manager. The following command overwrites the link (/usr/local/bin/docker):
#sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
To enable tab-completion of Docker commands in BASH, either restart BASH or:
#source /etc/bash_completion.d/docker.io
check docker process and docker version
#ps aux | grep docker
#docker -v
#sudo docker.io version
install the latest version
To install the latest version, we need to add the Docker repository key to our local keychain:
#sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 36A1D7869245C8950F966E92D8576A8BA88D21E9
Add the Docker repository to our apt sources list:
#sudo sh -c "echo deb http://get.docker.io/ubuntu docker main > /etc/apt/sources.list.d/docker.list"
check
#cat /etc/apt/sources.list.d/docker.list
Then, update and install the lxc-docker package:
#sudo apt-get update
install
#sudo apt-get install lxc-docker
check docker version and info again, now you see it is 1.4.1
#sudo docker -v
#sudo docker info
To verify that everything has worked as expected, we can check if Docker downloads the ubuntu image, and then start bash in a container:
#sudo docker run -i -t ubuntu /bin/bash
or
#sudo docker run -it ubuntu /bin/bash
you will find you login docker latest image via root
log out
#exit
We were able to start bash in a container. And we can check if the image for ubuntu is there:
#sudo docker images
3. Permission
permission or you actually can't find docker with error message.
check docker group first
#cat /etc/group
add user to docker group
#sudo gpasswd -a devdocker docker
Restart the Docker daemon:
#sudo service docker restart
log out and log in
#exit
***PS docker need to run root w/o required sudo cli***
4. Docker Commands
If you are starter, you can just type docker and it will list all the commands for you, or you can go docker site to study those commands. (https://docs.docker.com/reference/commandline/cli/)
#docker
docker search
#docker search --help
#docker search -s 10 jenkins
We got too many outputs, so we need to filter it out items with more than 10 stars:
#docker search -s 10 tomcat
docker pull
The pull command will go up to the web site and grab the image and download it to our local machine.
#docker pull --help
#docker pull ubuntu
docker images
Check what Docker images are available on our machine, we use docker images:
#docker images
Try download centOS
#docker pull centos:latest
check again
#docker images
docker rmi ( remove images )
remove image from our local machine via image id
#docker rmi 4986bf8c1536
remove all images
#docker rmi $(docker images -q)
PS: force remove images
[root@xxx ~]# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
hello-world latest 0a6ba66e537a 5 months ago 960 B
localhost:5000/myfirstimage latest 0a6ba66e537a 5 months ago 960 B
[root@xxx ~]# docker rmi -f 0a6ba66e537a
Untagged: hello-world:latest
Untagged: localhost:5000/myfirstimage:latest
Deleted: 0a6ba66e537a53a5ea94f7c6a99c534c6adb12e3ed09326d4bf3b38f7c3ba4e7
Deleted: b901d36b6f2fd759c362819c595301ca981622654e7ea8a1aac893fbd2740b4c
docker run
#docker run --help
check current local machine os
#cat /etc/issue
docker run centos - This will create container based upon the image and execute the bin/bash command. Then it will take us into a shell on that machine that can continue to do things:
#docker run -it centos:latest /bin/bash
now you are in the centos bash, log out from your centos
#exit
try busybox - "stripped-down Unix tools in a single executable file" - very tiny linux distribution, it runs in a variety of POSIX environments such as Linux, Android, FreeBSD, etc.
#docker run -it busybox sh
***can't do changing the command that's been executed***
for example echo Johnny Wang via docker run -it
#docker run -it echo 'Johnny Wang'
docker just run echo shell and exit, you see the status via docker ps -a
even you restart it and try to attach it, it will fail since it terminate after run echo command.
***ps if you run -it with the image local doesn't have, it will download image directly***
docker list container - ps
#docker ps
show running container
#docker ps -a
docker restart
we can restart the container via container id
#docker restart 6edc94951379 (container id)
docker attach
we can attach to a running container
#docker attach 6edc94951379 (container id)
docker remove
#docker rm 6edc94951379 (container id)
remove all container
#docker rm $(docker ps -aq)
remove container after run every time run -it --rm ( one time execution )
#docker run -it --rm busybox sh
#docker run -it --rm busybox echo "I will not staying around forever"
PS:don't have any container. By passing in --rm, the container is automatically deleted once the container exited.
docker kill
when you try to run an unstoppable container via docker run -t
#docker run -t busybox sh
you can attach but nothing there, now you would like to stop it.
#docker kill fd18db6a9223 (container id)
5. More Run Command
run -v for share file with local under root
binding a folder in our local machine (/home/k/myDocker) with the folder in Docker container (k) so that they can share files: ***-v /home/k/myDocker:/k busybox***
#docker run -it --rm -v /home/k/myDocker:/k busybox sh
run -p for attach file to run under port
Mapping host with port, using port 80 for nginx via auto assign.
#docker run -d -p 80 nginx
You can check the auto-mapping port via docker with ps -a command.
Then check the web app via browser.
run under specific port by request
#docker run -p 8099:80 -d nginx
Check web app via specific ports
run -e for run with environment variant
run -e DOCK_VAR=devdocker
#docker run -it --rm -e DOCK_VAR=devdocker busybox sh
5. Build Docker Images - mangoDB demo
There has two basic way to build your own Docker image. One is download image from docker forge and run image as container, then you can do the customization regarding your container then either you upload back to docker forge or you store it in your repository. The demo above has show the download and run container.
Another one is using dockerfile as scripting to customize your docker image automatically.
docker run build
Each Dockerfile is a script, composed of various commands (instructions) and arguments listed successively to automatically perform actions on a base image in order to create (or form) a new one. Dockerfiles begin with defining an image FROM which the build process starts. Here is the basic command.
#vim Dockerfile
#cat Dockerfile
FROM ubuntu
#docker build -t (Dockerfile) .
***watch out "." at the end.***
For me, Dockerfile is more like scripting for build an image, it is similar concept like some DSL. There are various other methods, commands and arguments (or conditions), in return, provide a new image which is to be used for creating docker containers. The scripting detail you can find in this link. (https://docs.docker.com/reference/builder/)
Here I would like to show a demo to use dockerfile to build a mangoDB automatically. I actually follow the steps on this site to simulate the process. (https://www.digitalocean.com/community/tutorials/docker-explained-using-dockerfiles-to-automate-building-of-images)
First of all, you need to prepare a Dockerfile for mangoDB. The copy you can find from above link.
#sudo vim Dockerfile
#docker build -t my_mongodb .
#docker run -name my_first_mdb_instance -i -t my_mongodb
if you would like to re-use the image, you can restart the image again and assign another container name for it.
Check image id
#docker ps -a
Restart image
#docker restart 46fd9933236d
Run another container
#docker run -name my_second_mdb_instance -i -t my_mongodb
PS: Even Docker fully leverage linux container, however Docker can still be running on Windows as long as leverage VM. Here has link from standard docker doc site (https://docs.docker.com/installation/windows/)
Last, I must share this funny pic with you. This is the best picture to describe what's Docker can do. Look the last one, Leo's face is so confusing !
Why use docker ( container )
Application-centric management:
Raises the level of abstraction from running an OS on virtual hardware to running an application on a virtual OS
The simplicity of PaaS with the flexibility of IaaS
Dev and Ops separation of concerns:
Provides separation of build and deployment
Decoupling applications from infrastructure
Agile application creation and deployment:
Increased ease and efficiency of container image creation compared to VM image use
Continuous development, integration, and deployment:
Facilitates reliable/frequent container image build/deployment with quick and easy rollbacks
Image immutability
Loosely coupled, distributed, elastic, liberated micro-services:
Applications are broken into smaller, independent pieces
Can be deployed and managed dynamically
Not a fat monolithic stack running on one big single-purpose machine
Environmental consistency across development, testing, and production: Runs the same on a laptop as it does in the cloud
Cloud and OS distribution portability:
Distros: Ubuntu, RHEL, SUSE, …
Clouds: AWS, Google Container Engine, Azure, Rackspace, …
Resource isolation:
Predictable application performance
Efficient resource utilization:
High efficiency and density
Movie Quote:
No body know where will we go, just follow the your instinct.
Cobb: You're waiting for a train. A train that'll take you far away. You know where you hope this train will take you. But you can't know for sure. Yet it doesn't matter. Now, tell me why?Mal: Because you'll be together! - (Inception) 2010
You dream always awaits you. It's up to you to decide when you'll go for it. - (Chef), 2014
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