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Omkar Sharma
Omkar Sharma

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The Only Docker Architecture & Installation Guide You’ll Ever Need

#docker #container #architecture #daemon

Docker Architecture ?

Docker Architecture

The above picture, clearly indicates that Docker Deamon is brain of Docker. If Docker Deamon is killed, stops working for some reasons, Docker is brain dead :p (sarcasm intended).

Docker LifeCycle

We can use the above Image as reference to understand the lifecycle of Docker.

There are three important things,

  1. docker build -> builds docker images from Dockerfile
  2. docker run -> runs container from docker images
  3. docker push -> push the container image to public/private regestries to share the docker images.

Docker

Understanding the terminology (Inspired from Docker Docs)

Docker daemon

The Docker daemon (dockerd) listens for Docker API requests and manages Docker objects such as images, containers, networks, and volumes. A daemon can also communicate with other daemons to manage Docker services.

Docker client

The Docker client (docker) is the primary way that many Docker users interact with Docker. When you use commands such as docker run, the client sends these commands to dockerd, which carries them out. The docker command uses the Docker API. The Docker client can communicate with more than one daemon.

Docker Desktop

Docker Desktop is an easy-to-install application for your Mac, Windows or Linux environment that enables you to build and share containerized applications and microservices. Docker Desktop includes the Docker daemon (dockerd), the Docker client (docker), Docker Compose, Docker Content Trust, Kubernetes, and Credential Helper. For more information, see Docker Desktop.

Docker registries

A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker is configured to look for images on Docker Hub by default. You can even run your own private registry.

When you use the docker pull or docker run commands, the required images are pulled from your configured registry. When you use the docker push command, your image is pushed to your configured registry.
Docker objects

When you use Docker, you are creating and using images, containers, networks, volumes, plugins, and other objects. This section is a brief overview of some of those objects.

Dockerfile

Dockerfile is a file where you provide the steps to build your Docker Image.

Images

An image is a read-only template with instructions for creating a Docker container. Often, an image is based on another image, with some additional customization. For example, you may build an image which is based on the ubuntu image, but installs the Apache web server and your application, as well as the configuration details needed to make your application run.

You might create your own images or you might only use those created by others and published in a registry. To build your own image, you create a Dockerfile with a simple syntax for defining the steps needed to create the image and run it. Each instruction in a Dockerfile creates a layer in the image. When you change the Dockerfile and rebuild the image, only those layers which have changed are rebuilt. This is part of what makes images so lightweight, small, and fast, when compared to other virtualization technologies.

INSTALL DOCKER

A very detailed instructions to install Docker are provide in the below link

https://docs.docker.com/get-docker/

For Demo,

You can create an Ubuntu EC2 Instance on AWS and run the below commands to install docker.

sudo apt update
sudo apt install docker.io -y
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Start Docker and Grant Access

A very common mistake that many beginners do is, After they install docker using the sudo access, they miss the step to Start the Docker daemon and grant acess to the user they want to use to interact with docker and run docker commands.

Always ensure the docker daemon is up and running.

A easy way to verify your Docker installation is by running the below command

docker run hello-world
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If the output says:

docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post "http://%2Fvar%2Frun%2Fdocker.sock/v1.24/containers/create": dial unix /var/run/docker.sock: connect: permission denied.
See 'docker run --help'.
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This can mean two things,

  1. Docker deamon is not running.
  2. Your user does not have access to run docker commands.

Start Docker daemon

You use the below command to verify if the docker daemon is actually started and Active

sudo systemctl status docker
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If you notice that the docker daemon is not running, you can start the daemon using the below command

sudo systemctl start docker
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Grant Access to your user to run docker commands

To grant access to your user to run the docker command, you should add the user to the Docker Linux group. Docker group is create by default when docker is installed.

sudo usermod -aG docker ubuntu
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In the above command ubuntu is the name of the user, you can change the username appropriately.

NOTE: : You need to logout and login back for the changes to be reflected.

Docker is Installed, up and running 🥳🥳

Use the same command again, to verify that docker is up and running.

docker run hello-world
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Output should look like:

....
....
Hello from Docker!
This message shows that your installation appears to be working correctly.
...
...
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✍️ Author: Omkar Sharma

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