Docker Tutorial Part 4 -> Understanding components: docker-machine, Dockerfile, Images and Containers

In our previous blog post Docker setup and installation on Ubuntu , we have done installation of docker. Now before diving deep in to hands on of Docker, its time to understand what are all components or terminology.

Following are some major components of Docker-

  1. Docker-Machine
  2. Docker Engine
  3. Dockerfile
  4. Docker Images
  5. Docker Containers

Docker-Machine – This can also be referred as Docker Host. If you are working on a Linux machine then your Linux system itself is a Docker-machine / Docker host. But if you are working with Boot2Docker on windows, then your Linux VM inside Oracle virtual box is the docker-machine. In case of Windows(Boot2Docker), you can have multiple docker-machine and can also create new using below command-

docker-machine create --driver virtualbox <suitable machine name>

Docker Engine – Docker engine is the core of Docker, it is the main software/package which drive all docker commands and enable user to create images and containers. This is a lightweight and powerful open source containerization technology combined with capabilities to build and ship your applications

DockerFile – Dockerfile is a plain text file with no extension. It has series of  instructions which needs to be perform to create a docker image. Instruction are some docker specific commands which when executed in sequence generates a docker image. If you have a dokerfile, you can easily create an image from it with a custom name. Every instruction when executed, stored in a layer. A sample dockerfile with python looks like below-

FROM ubuntu:14.04
RUN apt-get update && \
apt-get install -y python python-dev python-pip python-virtualenv && \
rm -rf /var/lib/apt/lists/*
WORKDIR /data
CMD [“bash”]

Docker images – Docker image is a blue print of what you need in a container. Docker image is build up from a series of layers. Each layer represents an instruction in the image’s dockerfile. Each layer except the last one is read-only. To understand the concept at high level, you can consider an image as a Class and container as object of that class. Object is a run time entity similar to container. Like a class can have many objects of it, An image can have multiple containers out of it.

Docker container – Docker container is a lightweight execution environment to build and ship your application. This is just your docker image in action.

Lets understand the difference with an analogy. Consider your Dockerfile as some Abc.java file. Now when you build/compile Abc.java file you get .class file (docker image). Now when you can create multiple objects(containers) of class Abc.java(docker image), and these objects can be referred as Docker containers. So in the end the run time entity on which you will actually work is Container.

In the next blog post , we would be learning about running your local source code in to container

To know more in details, hands-on and for personal / corporate training please reach out to – gauravtiwari91@yahoo.com

Docker Tutorial Part 3 -> Setup and installation on Ubuntu

Installing docker on Linux is as simple as installing any other Linux package, We don’t require the whole Docker toolbox for working with docker on Linux.

In this blog post, I will be talking about installing community edition installation of Docker.

To install Docker, you need the 64 bit version of either one of below Ubuntu-

  • Xenial 16.04 (LTS)
  • Trusty 14.04 (LTS)
  • Yakkety  16.10

Uninstall older version of Docker – Older version of Docker called docker or docker-engine. if you have these then uninstall them, otherwise skip this part

sudo apt-get remove docker docker-engine

Install Docker – You can install the Docker in different ways, as per your needs

  1. Setup docker repositories and install from them – this is easy in installation and upgrades (recommended approach)
  2. Download the DEB package and install it manually and also manage upgrades manually (prefer when lack of internet access)

Install using Repository – If you are doing the setup for the first time on a new host machine, you need to setup the docker repository. Then you can use the same repository for install and updates

  • Install packages to allow apt to use a repository over HTTPS:
sudo apt-get install apt-transport-https ca-certificates curl software-properties-common
  • Add Docker’s official GPG key :
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
  • Verify that the key fingerprint is 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88
sudo apt-key fingerprint 0EBFCD88

pub   4096R/0EBFCD88 2017-02-22
      Key fingerprint = 9DC8 5822 9FC7 DD38 854A  E2D8 8D81 803C 0EBF CD88
uid                  Docker Release (CE deb) <docker@docker.com>
sub   4096R/F273FCD8 2017-02-22
  • use the below command to setup the stable repository
sudo add-apt-repository \
   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
   $(lsb_release -cs) \
   stable"
  • Update the apt package
sudo apt-get update
  • Install the latest / specific version of Docker with below commands
sudo apt-get install docker-ce   //for latest version
sudo apt-get install docker-ce=  //for specific version
  • Verify that Docker CE is installed correctly by running a sample hello-world docker image-
sudo docker run hello-world
  • You should see something like below if your installation is successful and complete

docker-linux

If you guys face issues in installation , please mention in comments section.

In the next blog post , we would be learning docker terminology and different docker components

To know more in details, hands-on and for personal / corporate training please reach out to – gauravtiwari91@yahoo.com

Docker Tutorial Part 1 ->Docker technology overview: How is it different from virtual machines

Before we start blindly follow the docker training program and start learning it. Lets understand why we should learn, why we need it. What this technology is and how it works.

What is Docker – All applications have their own dependencies, which include both software and hardware resources. Docker is an open source platform for developers, QA etc. Its a mechanism that helps in isolating the dependencies per each application by packaging them into a single unit called container. Containers are safe to use and deployed easily compared to previous approaches

How containers are different as a concept – Lets understand the difference by an analogy. Consider your virtual machine as a house and container as an apartment.

Houses (Virtual machines) are fully self-contained which has its own infrastructure- plumbing, electricity, water supply etc. On a majority all house would have at least a bedroom, living area, bathroom and kitchen. Still, even if I am trying to bought a house with only a room, I would end up buying more than what i need in a house.

Apartments (The containers) are built around shared infrastructure. The apartment building (Docker host) shares plumbing, electricity, water supply etc. They are also offered in different sizes as per your need. You also have to pay for only those services which you want to use.

Also maintenance cost for house will always be higher than an apartment.

So with containers, you share the underlying resource of the Docker host and use only the software which you need to run your application.

And with virtual machines- its just opposite, you are going to have full operating systems and default programs comes with it.

Now when we have understand the concept, lets go a little technical. Consider the building as docker-host and builder as docker-engine in below explaination-

Docker containers versus Virtual Machines – Virtual machines have full OS with its own memory management with the overhead of virtual device drivers. In an virtual machine, valuable resources are emulated for the guest OS and Hypervisor, which makes it possible to run many instances of one or more operating systems in parallel on a single machine

While Docker containers are executed with Docker engine rather than a Hypervisor, therefore containers are smaller than virtual machines and enable faster startup and better performance, great compatibility due to sharing of the host’s kernel. Architecture level visual difference is as below – containersvsVM

So to optimize our SDLC and reduce time spent in test script execution,overhead of maintaining the execution/deployment environments, We should really go for container technology.

Now we know what docker is and why we should use it. To know more in details and for personal / corporate trainings please reach out to – gauravtiwari91@yahoo.com