An intro to Docker

DockerNotes

What is Docker?

 - Docker is used for containarization.
 - Docker runs the specific software or in this case an image without being installed in the system
 - Docker is like mini containers of os running softwares inspite of any Operating system
 - It helps to run multiple servers and softwares and many more..

What it Does?

  - It isolates(Namespace) the resources[Processes, HardDrive, Users, InterProcessComm, Network] available from the system
  - The namespaces resources are controlled by the ControlGroups[Memory, CpuUsage, NetworkBandwidth, HD i/o]
  
Docker Image:

  - It contains Software Snapshot and Startup command
                
                build                      run 
  DockerFile ------------> Docker Image ----------> Docker Container
  
Command Cheat Sheet::

  => docker run <imageName> <Overide Cmd> ===> Starting a container
  => docker ps ===> Listing the containers 
  => docker ps -a ===> Listing history of containers
  => docker create <ContainerName> ===> Combining both is the run command
  => docker start -a(attaching the output) <ContainerName>  ===/\
  => docker system prune ===> Remove everything related to docker
  => docker logs <containerId> ===> Check the log
  => docker stop <containerId> ===> Sends 'SIGTERM' termination signal to the process and cleanup and normal stopping process
  => docker kill <containerId> ===> Kills process without additional ops
  => docker exec -i(input => stdin) -t(output => stdout) <containerId> <command> ===> Running command inside a container ===> docker exec -it <id> redis-cli
  => docker run -it <image> sh ===> Create,Start,OverideCommand,RunShell at the start
  => docker rm <container> ====> Remove a container
  => docker rmi <image> =====> Remove an imgae
  => docker images =====> Show all the images
  => docker pull <image> =====> Only update the container with latest version without running
  => docker run -p <accessPort>:<containerPort> <container> => Port Mapping
  => docker run -d <container> =====> Run the container in the background 
  => docker attach <containerId> =======> Attach the terminal back again
  => docker run <image>:<version> ======> Get the specified version
  => docker run -v <backupPath>:<containerPath> <image> ====> Run the volume of the container in different disk path
  => docker inspect <container> =======> Get details of the container in JSON format
  => docker logs <container> =========> Get the container logs
  => docker run -e <envVariables> <container> =====> Set the environment varibles
 
 Flags
  -t   Name
  -f   Path
  -it  Interactive
  -d   Detached
 
 Docker Image:
 
  => Create a DockerFile(INSTRUCTIONS and ARGUMENTS)
  => Write the steps needed to run the application
  => docker build DockerFile -t <tagName> ====> Building the image from the file
  => docker push <tagName> =====> To publish the image in cloud
  => FROM is the firstline(always) - Base Image
  => Docker preserves the cache and provides rollback for steps in DockerFile
  => ENTRYPOINT => For appending the arguments in the command 
     Eg: FROM Ubuntu
         ENTRYPOINT ['sleep']
         CMD ['5'] ===> default value
         docker run <container> 10 ===> pass the sleep value as the entrypoint argument and it gets appended
         docker run --entrypoint sleep2.0 <container> 10 ===> To change the entrypoint value
         docker  -t name -f path . currentLocation
         
  Basic variables
  
   FROM - Os for the container
   RUN  - Running cmd for installation (Executes at build time)
   CMD  - (Ignored if docker run with params)(Only last CMD is executed)
   ENTRYPOINT - (Appends the packages from the command) --> docker run <img-name> git httpd telnet tree
   WORKDIR - Change working directory 
   COPY - 
   ADD  -
   EXPOSE - Exposing the port for host
   ENV - 
   
 Docker Network:
  
  => Docker has a built in DNS server for mapping the container name with default of 172 series
  => Docker uses network namespaces within the container (virtual ethernet pair)
  => docker network ls ====> View all the network in the container
 
 Dokcer Storage:
 
  => Structure:-
     |--/var/lib/docker
       |- /auf
       |- /containers
       |- /image
       |- /volume
  => docker volume create <vol_name> ====> create a volume as above structure
  => docker volume ls ====> listing the volumes
  => docker inspect <volume hash / name> ====> Check the metadata of the volume
  => Volume Mount and Bind Mount 
  => docker run -v </with full path>:/var/lib/<image> ==> Bind mount
  => docker run / --mount type=bind, source="path", target="path" <container>
  
  Anonymous Volumes --> docker run --name <cont-name> -v /data01 nginx /bin/bash
  Named Volumes ------> docker run --name <cont-name> -v <vol-name>:/data01 nginx /bin/bash
  Host/Bind Volumes ---> mkdir /data/docker_data ==> docker run --name <cont-name> -v /data/docker_data:/data01 nginx /bin/bash
   
Docker Compose:

  docker-compose up

  docker-compose down

  docker-compose up -d

  docker-compose ps

  docker-compose logs

  docker-compose exec web sh

  curl localhost

  (edit Dockerfile, and add RUN apk add --update curl)

  docker-compose up -d

  docker-compose up -d --build

  docker-compose exec web sh

  curl localhost:port

  docker-compose down