Understanding Docker Containerization

Why Docker?
VM vs Containers

• VM and Containers provide separate isolated environments for running applications.

• VM requires complete OS leading to lot of storage taken whereas Containers are lightweight which includes all dependencies of app, libraries and system dependencies

• VM run in isolation with their own resources while Containers also run in isolation but share host OS kernel

• Both VM and containers - snapshot the current configuration ( allows for easy restoration to a previous point / for creating new instances with same configuration)

• Container provides a runtime environment

• Containers can be easily shipped.

DOCKER:

Docker is a containerization platform easy way to containerize the applications, can build container images. Easy to install and run new software without worrying about setup & dependencies. Its a Package software that has everything to run application like libraries, system tools, code etc...

Container: instance of image runs a program.

Docker file: set of instruction to build images.

Docker Client (CLI) - tool that we are going to issue commands

Docker Daemon/Docker server: tool that helps builds image, run container etc..

Namespace - Area of hard drive is for this process where as Control group (C group) - is limit amount of memory the process to be used, CPU, Network, HD I/O

Docker images: snapshots of libraries & dependencies of application to run in a container
Docker daemon: Background process that manages docker images, containers, network & storage volumes.
Docker client: command line to interact with daemon
Docker registry: holds all the versions of a specific image. Users can pull locally and push images to registry.

Files and folders in base image:

/bin - binary executable files (Is,cp)
/sbin - system binary executable files (init, shutdown button)
/etc - configuration files for various system service
/lib - library files that are used by binary files
/usr - user relate files (application)
/var - variable data(log files
/root -home direct for root user

These above files provide logical isolation from one container to another container.

Files & folders from host OS:

-host file system (address network node in a computer network(IP address), text file used to map host name, IP address)
-Networking stack - provide network
-system calls - Containers interact with host's kernel through system call interface
-Namespaces - Docker container use Linux namespace to create isolation(file system, process ID, network)
-control group - limit/control resources amount(CPU, memory, I/O) that containers should access

Installing Docker on ubuntu in Aws

Updating package index
Step 1: sudo apt-get update
Installing docker
Step 2: sudo apt-get install docker.io -y
Starting the docker service
Step 3: sudo systemctl startlocker
Step 4: sudo docker run hello-world Step 5: docker-version
Add user to docker group - to use docker cmd without 'sudo' :
sudo usermod -a -G docker $(whoami)
activate changes without logging out:
newgrp docker
enabling docker service - sudo systemctl enable docker
Troubleshoot:
docker images
permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get "http://%2Fvar%2Frun%2Fdocker.sock/v1.24/images/json": dial unix/var/run/docker.sock: connect: permission denied

solved by: sudo chmod 666 /var/run/docker.sock

Steps to setup EC2 instance locally using SSH:
step 1:
ssh-keygen -t rsa -b 4096 -C thil--a---@gmail.com

chmod 600 <keypair>.pem

step 2:
ssh -i path/to/key/keypair.pem ec2@54.2fg3.168.20x

ssh -i /path/to/key-pem <ubuntu/ec2 instance>@<54.86/public key>

Dockerfile creation, building images, container creation and pushing to registry.

Step 1: create a Dockerfile

FROM ubuntu:latest
# Update the package repository
RUN apt-get update

Step 2: Build Docker Image
Build the Docker image using the docker build command:

docker build -t <IMAGE-NAME>:<TAG> <PATH-TO-THE-DOCKERFILE>

Example: docker build -t thilaga-image:latest /path/to/sampledockerfile

Step 3: Create Container from Image
Once the image is built, use the docker run command to create a container from the created image:

docker run -d --name <CONTAINER-NAME> -it <IMAGE-NAME/ID>

Eg: docker run -d --name cont1 -it thilaga-image

Step 4: Login to Container
Login to the container using the docker exec command:

docker exec -it <CONTAINER-NAME/ID> <TYPE-OF-LOGIN>
# Ping another container
Ping cont2

Example: docker exec -it cont1 bash
Inside the container:

Step 5: Docker Login and Push
Login to Docker Hub using the docker login command, then push the image to Docker Hub:

Docker login

docker push <USERNAME>/<IMAGE-NAME>

Example: docker push thilaga/thilaga-image

Basic commands which would help:
docker ps: List currently running containers.
docker ps -a: List all containers, including those that have exited.
docker images: List all active images.
docker inspect <contname>: Retrieve specific details about a container.
docker network ls: List Docker network bridges.
docker network inspect <bridge_sample>
docker network rm <bridge_sample> docker stop <cont_id> docker rm <cont_name> docker rmi <image_name> docker logs <container_id>: Retrieve logs generated by a specific container.
docker system prune: Clean up Docker environment by removing stopped containers, unused networks, dangling images, and build cache.

Docker swarm - Docker is a platform where you can create container and run in isolation manner whereas docker swarm is used to manage and orchestrate containers.

Container port mapping

docker run -p 5000:6000 <image name>

Multi-container Docker environment
One container talk to other container using Network bridge
Docker compose:
There are different tools plays role in docker
1. Docker machine
2. Docker compose - tool for running multi container docker applications
3. Docker swarm - a native clustering solution for docker
4. Kubernetes - open source tool for automating deployment, scaling and application code