DEV Community: taragurung

Creating container from docker image (Part-2)

taragurung — Mon, 20 Jan 2025 17:16:15 +0000

If you have read Part-1 we are clear:

We need docker image to create docker container
We can create our own image or use docker images made by others

Where do we find the images built by others:

The place where docker images are stored is called Docker Registry. Few widely used docker registries are:

Docker hub
AWS ECR (AWS Managed Service)
GCP container service (GCP Managed Service)

_Here, we will learn to run docker container pulling pubic docker images from DockerHub _(https://hub.docker.com/) for simplicity purpose.

From docker registry to docker container

fig: How images are pulled and runs as docker container

Search for the docker images in DockerHub (hub.docker.com). Type the name of the image you are looking for. For example: nginx, choose the one that best fits your requirement
Pull the image
Run it.

Note: When running docker container if the image is not found it will automatically look for the image and pull

Docker command to pull image

This command will pull public docker image named as nginx from docker registry.

docker pull nginx

If you want to pull specific version of docker image then we pass it after image name as shown in example bellow, and its called as tag. If no tag is provided then it will use latest as the default tag.

docker pull nginx:1.27.3-alpine
All the available tags will be listed in docker registry

docker command to run docker container from pulled image

docker run -itd --name mynginx nginx
Here:

itd refers to: interactive mode, terminal mode and detached mode. (more on this later)
mynginx refers to name of the container passed after --nameargument
nginx refers to the image name

Few must know docker commands:

Now, you are familiar with how to run docker containers from docker images but that's not enough.

Running a docker container

docker run -itd nginx

Checking running containers

docker ps

Checking locally available docker images

docker images

Assigning ports

docker run -itd -p 8000:80 nginx

Getting inside docker container for debugging or similar to sshing into server

docker exec -it <container-name / id > sh or bash

Checking docker logs

docker logs <container-name / id> -f

Inspecting for getting detailed information about container

docker inspect <container-name / id >

Stopping the container
stopping docker container when not required

docker stop <container-name/id>

Conclusion:

We need docker image to create docker container.
docker images are stored in registries.

Problem Docker solves, installation guide (Part-1)

taragurung — Mon, 20 Jan 2025 16:11:14 +0000

Docker is revolved around 2 major issues:

1- The Application that runs on my machine is not quite guaranteed to run on another machine.
2- Setting up a new environment is a time-consuming process.

There are numerous benefits of using docker but we will discuss that later.

To understand Docker effectively, it's important to first explore the fundamentals of virtualization and containerization. However, before diving into those concepts, let’s get started by setting up Docker on your system.

Virtualization and Containerization in next chapter

Setting up docker in Linux machine

Installing with apt

sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Add the repository to Apt sources:
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update

Install the latest version

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Verify installation:

docker --version

Official installation documentation here: https://docs.docker.com/engine/install/ubuntu/

Here, I have shown how to do it on Ubuntu Server. Depending upon your Os type you can follow the official documentation guide.

Setting up docker in Macos machine

Visit this url https://docs.docker.com/desktop/setup/install/mac-install/
Choose the correct version for your processor (Apple Silicon or Intel). If you have m1 chip download from the button that says Docker Desktop for Mac with Apple Silicon if not use another button to download.
Open the downloaded .dmg file and install
Open Docker from the Applications folder or Spotlight search.
Grant necessary permissions if prompted.
Sign in with your Docker Hub account or create one if you don’t have it.

Setting up docker in Windows machine

1. Download Docker Desktop:

Visit the Docker Desktop for Windows page. https://docs.docker.com/desktop/setup/install/windows-install/
Download the installer, depending upon your Windows type. AMD or Arm

2. Install Docker Desktop:

Run the installer and follow the setup wizard.
When prompted, ensure Use WSL 2 instead of Hyper-V is selected (if you're on Windows Home).
Restart if necessary.

3. Launch Docker Desktop:

Open Docker Desktop from the Start Menu.
Sign in with your Docker Hub account or create one.

Back to the problem, how docker solves the issues of incompatibility:

To make it easy to understandable let's put it like this. I drew one sketch and asked another guy to draw the same, he might be able to but will of course be hard for him to have an exact copy of mine.

The solution could be,I will provide him sketch as a base image to follow and just ask to do photocopy of it instead of drawing it again which will solve the two problems:

Now the duplicate sketch will be exact the same
Secondly, it will save a lot of time for him.

We have a similar concept in docker we create a base image first keeping all the application codes and dependencies which will then be used to create a docker container.

Dockers Basic two concepts to understand:

Docker image:

We need the docker image to run an application as docker container.
It's a process of attaching all the codes and dependencies required by the application.
We can either create our own docker images or use those pre-built by someone and publicly available. We will learn later how to create a docker images.

Docker container:

We run a docker image which when runs is termed as docker container.

Final though: we compact everything into docker image which can be transferred to any machine and is guaranteed to have the same codes and dependencies and run without any configuration hassle.