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DOCKERIn brief
THE QUESTIONS Does Docker replace
VM? What does it do? Is Docker useful for
developers or only for system admins?
What problems does it solves?
WHAT IS VM? A virtual machine (VM) is an operating system or
application environment that is installed on software, which imitates dedicated hardware.
The end user has the same experience on a virtual machine as they would have on dedicated hardware.
Specialized software, called a hypervisor or Virtual Machine Monitor, emulates the PC client or server's CPU, memory, hard disk, network and other hardware resources completely, enabling virtual machines to share the resources.
Virtualization limits costs by reducing the need for physical hardware systems.
WHAT IS DOCKER? Docker is a tool designed to make it easier to
create, deploy, and run applications by using containers.
Docker containers wrap a piece of software in a complete filesystem that contains everything needed to run: code, runtime, system tools, system libraries – anything that can be installed on a server.
Containers running on a single machine share the same operating system kernel.
It gives a significant performance boost and reduces the size of the application.
Docker gives you the ability to snapshot the OS into a shared image, and makes it easy to deploy on other docker hosts. Locally, dev, qa, prod, etc.: all the same image.
VM VS DOCKERVirtual Machines DockerEach VM has its own OS Shares the kernel with other
containersVirtual machine images are significantly large
Containers have much smaller footprint comparatively.
A virtual machine could take up several minutes to create and launch.
A container can be created and launched just in a few seconds
Benefits: security and isolation. Benefits: easier and more lightweight to deploy and faster to start up
In IaaS use cases, machine virtualization is an ideal fit.
Containers are best suited for packaging/shipping portable and modular software
IN GIST Clearly—for DevOps and CI/CD initiatives—application portability and
consistency are crucial needs that Docker fulfills quite nicely. Simply put, containers provide OS-level process isolation whereas virtual
machines offer isolation at the hardware abstraction layer. Again, the two technologies can be used in conjunction with each other for
added benefits—for example, Docker containers can be created inside VMs to make a solution ultra-portable.
For now, Docker doesn’t replace VM.
USAGE OF DOCKER Use Docker as version control system for your entire app's operating
system Use Docker when you want to distribute/collaborate on your app's
operating system with a team Use Docker to run your code on your laptop in the same environment as
you have on your server (try the building tool) Use Docker whenever your app needs to go through multiple phases of
development (dev/test/qa/prod) Use Docker with your Chef Cookbooks and Puppet Manifests
ALTERNATIVES The Amazon AMI Marketplace is the closest thing to the Docker Index that
you will find. With AMIs, you can only run them on Amazon. With Docker, you can run the images on any Linux server that runs Docker.
The Warden project is a LXC manager written for Cloud Foundry without any of the social features of Docker like sharing images with other people on the Docker Index
WHY DOCKER IS CHANGING THE FACE OF DEVELOPMENT? The collaboration features (docker push and docker pull) are one of the
most disruptive parts of Docker. With Docker pull/push the developers and ops guys, have first time been
able to easily collaborate quickly on building infrastructure together. The developers can focus on building great applications and the ops guys
can focus on building perfect service containers. The app guys can share app containers with ops guys and the ops guys can
share MySQL and PosgreSQL and Redis servers with app guys.
EVERYDAY CHALLENGES
It works on my machine but not on
yours
I have been helping the [new hire] setup her
environment all day
I can’t try it because IT
hasn’t updated dev-environment
I have to work directly on production
environment to fix this issue.
WAYS TO USE DOCKER
Create a local Docker
container
Distribute it to private or
public collaborators
Enhance collaboratively
Create a production
Docker image
Pull it in local development environment.
Work on “just like prod”
environment
Keep multiple Docker images
Switch between Docker
images as you switch
projects
Be more productive
Release new Docker
image per product release
Keep the system
inconsistencies in Limit
Be more consistent
DOCKER TERMINOLOGIES Container - a runtime instance of a Docker image. Image - an ordered collection of root filesystem changes and execution
parameters for use within a running container. Layer - a “slice” of the container filesystem; one layer is created by each
Dockerfile instruction. Dockerfile - a text script that contains the commands you execute to build
a Docker image. Registry - a repository of images. It can be public or private. This is a web
service.
DOCKER IMAGES AND CONTAINERS
DOCKERFILE Docker can build images automatically by reading the instructions from a
Dockerfile. A Dockerfile is a text document that contains all the commands a user
could call on the command line to assemble an image. Using docker build users can create an automated build that executes
several command-line instructions in succession.
EXAMPLE OF A DOCKERFILEFROM ubuntuMAINTAINER MyNameRUN apt-get updateRUN apt-get install -y nginxCOPY index.html /usr/share/nginx/html/ENTRYPOINT [“/usr/sbin/nginx”,”-g”,”daemon off;”]EXPOSE 80
Select the base image
Set the author
Add new layer on the image
specify the default app that you want to run
WORK-FLOWBuild An Image
$ docker build -t gvacca/nginx .
Store image in a registry (public, e.g. Dockerhub, or
private)
$ docker push gvacca/nginx
Pull image on the target host
$ docker pull gvacca/nginx
Run container on the target host
$ docker run -it gvacca/nginx
SOME IMPORTANT DOCKER TOOLS Docker Machine: Provides a CLI to quickly provision a Docker Host.
Deploys locally or on a Cloud Provider AWS, Azure, GCE, DO, Rackspace, VMWare, etc…
Docker Registry: Store and distribute your docker container images. Docker Hub makes it easy: hub.docker.com.
Docker Swarm: Exposes several Docker Engines as a single virtual Engine. Serves the standard Docker API. Swarm is production ready Docker CLI.
DOCKERHUB Docker Hub is a cloud hosted service from Docker that provides registry
capabilities for public and private content. In Docker Hub, you usually put Docker Images that can be used/searched
by other Docker users. Docker Hub lets developers store and distribute their images with ease. You
can search some ready to go building blocks for your infrastructure. Quickly create an organization, add users or create groups of users to
collaborate with your repositories. Browse and search any public Docker image repositories for popular
content. Share your images with the community or host in private repositories for
secure collaboration with your team
