What is Docker?

Containers vs VMs

• a container is a packaging of software code with just the operating system (OS) libraries and dependencies required to run the code to create a single lightweight executable
• more portable and resource-efficient than virtual machines (VMs)
• In simple words these can be consider tiny units of machine responsible for running an instance of application

the core difference in VM and Containers are containers virtualize the OS while VMs virtualize the hardware, hence containers are lightweight and faster to run!

Feature	Containers	Virtual Machines
Virtualization Level	Operating System (OS) layer	Hardware layer
Resource Usage	Lightweight, fewer resources	Resource-intensive, higher overhead
Startup Time	Fast (seconds)	Slower (minutes)
Isolation	Process-level isolation	Full OS isolation
Kernel	Shares the host OS kernel	Each VM has its own kernel
Portability	Highly portable, move easily	Less portable, larger images

What is Docker?

• an application for developing, shipping and running applications in containers, simplifies the process of container management!
• helps to containerize an application and containers could be as low as 50MB.
• simply put docker is a way of containerizing an application but is a better alternative than creating a VM!

docker can be run by both docker desktop and rancher read rancher-desktop vs docker-desktop

components of docker

• dockerfile - is a script containing a series of instructions and commands for building a docker image
• image - blueprint for creating containers
• container - a container that runs on the docker daemon

dockerhub is a repository for storing docker images just like github stores codebases

commands

docker ps # list running containers
 
docker ps -a # list all containers
 
docker images # list all images
 
docker pull {image}:tag # pull an image with a specific tag
 
docker run {image}:tag # run a container using an image
# if the image is not present it fetches it first
 
docker run -d {image}:tag # run in detached mode - no logs
 
docker logs {container-id} # print logs
 
docker run -d -p 8080:80 nginx 
# forwards container port 8080 -> port 80 of localhost
 
docker build -t {name}:tag .
# build the docker image from the dockerfile in pwd
 
docker exec -it <container_id or name> /bin/bash
# enter docker container

Links:

containerization docker

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