DockerDocs.log

1.Docker is a platform or ecosystem(Docker Client, Server,Machine, Images, Hub, Compose) around creating and running containers
2. docker run hello-world. Steps.. docker CLI connects to docker server looks for hello-world image in Image Cache, if not present, then goes to docker Hub to fetch the image and download it and create a container.
3. different processes on your computer (chrome, terminal, sptoify, nodejs etc..) make a system call to the OS KERNEL.. which then distributes the request among the system CPU , memory, hard disk etc.
4. Namespacing and contol groups are used (belongs to Linux OS). Installing docker means installing a Linux Virtual Machine, which ahs its own KERNEL
5. If there is no change in the file structure then the image from the cache is used otherwise a new image is built and snapshot is taken frp the next set of commands

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DOCKER COMMAND:
1.docker run busybox echo hieeee,,,,,, docker= reference to docker client, run=  try to create and run a container from the image, busybox= name of the image, echo= default command to print something, hieee= string to be printed
02. docker ps,,,,, lists currently runnnig containers
03. docker ps --all,,, all containers which were ever started on our machine
04. docker create imageName,,,,, to create container, returns nothing just the id of the container
05. docker start imageName,,,,, to start a container, returns nothing just the id of the container
06. docker start -a imageName,,,,, -a flag looks for output from that container
07. docker system prune,,,, removes all stopped containers, build Cache, unused networks, dangling images
08. docker logs idOfContainer,,,, to retrieve logs of that container which ahas run and stopped
09. docker stop idOfContainer,,,, gives SIGTERM signal, to complete some final process and then stop the container
10. docker kill idOfContainer,,,, gives SIGKILL signal, to immediately stop the container
11. docker exec -it idOfContainer command,,,,, exec= to execute extra set of commands in a container, -it flag = -i for input , -t for giving output in pretty text 
12. docker exec -it idOfContainer command,,,,, sh= to run a shell
13. two different containers have totally different file systems
14. docker build . ,,,,,,, build= build from docker file, .(dot) = take all things from docker file
15. docker build -t dockerCustomTagName/ProjectName:version . ,,,,,,, -t =  tagName for the docker conatiner we building, so that we don't have to deal with Id everytime
16. docker run -p XXXX:YYYY idOfContainer or tagName,,,,,, -p =port mapping flag, XXXX= port on the local host to be mapped with port YYYY in the container
17. docker build -f Dockerfile.dev .  ,,,, -f = tag to use a different file altogether to build the docker container
18. docker run -p 3000:4000 -v /app/node_modules -v $(PWD):/app idOfContainer ,,,,,,, -v = used to create volumes , $(PWD) = refers to the current working directory of , : = used for mapping of one volume to other... meaning we want to map a folder inside the container (here app folder) to outside the container (here present working directory), so if the container wants to access anyting inside app folder of the container, ther it will reach to pwd on the local machine. Also, additional -v /app/node_modules means that we are not doing any mappping here, we just want to create a reference for this folder inside the cntainer.
19. docker attach containerId,,,,, used to attach to primary processes (stdin,stdout,stderr etc) in that container via terminal. We never attach to the secondary process which is generally created by the primary process (here npm looks at our provided arguments and creates this)
20. we can have different sections in 1 docker file (ex build phase, run pahse) 

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INSIDE DOCKER FILE :
01. FROM imageName as PhaseName,,,,,, FROM alpine image.... phaseName is builder phase
02. RUN add some dependency,,,,,, RUN  npm install
03. WORKDIR ,,,, to do all the dockerFile configurations in this directory
04. COPY something from somewhere... copy --from=builder /app/foldername...... here builder is phaseName
05. CMD ["string1", "string2", "string3",.....],,,, the commands to run when the container is finally ready with all dependencies and files

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INSIDE DOCKER COMPOSE FILE:
01.This file is used to give internal network connection betweeen multiple applications (ex nodejs, redis, react etc..) running in different containers so ṭhat they can inteact between themselves and exchange data. 
02. Its a separate CLI that gets installed along with docker. Its used to start up multiple docker containers at the smae time. docker-compose.yml Inside a yml file indetation is to be taken care of

03. version : version of the build
04. services : indented list of service to be run (ex nodejs, redis, react etc..) 
05. image : to use some image from docekr hub
06. build : . (dot) to build from docker file, 
06--a context : from where do we want all the files and folders to be pulled from to create the image, --b dockerfile : Docekrfile.dev file name
07. ports : -"4001:8001" for mapping
08. restart : always
09. volumes : -/app/node_modules ....  .:/app
01. command : ["string1", "string2", "string3",.....]

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DOCKER COMPOSE COMMAND:
01. docker-compose up,,,,,,  to run the docker image
02. docker-compose up --build,,,, to builda the image and then run it
03. docker-compose up -d,,,, -d= flag to run docker image in background
04. docker-compose down,,,, to stop 
05. docker-compose ps,,,, to list staus of all conatiners

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RESTART POLICIES:
1. "no" -never attempt to start the container even if it crashes. Has to user double quotes, bcz in yml file no is considers as boolean false
2. always - if container stops for any reason , always attempt to restart it
3. on-failure - if conatiner stops with some error code
4. unless-stopped - always start unless the developer forcibly stops it


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NPM:
01. npm run start - start development server. for development use only.
02. npm run test - run tests associated with the Project
03. npm run build - build a production version of the application   

Nginx is web server