CS/클라우드컴퓨팅

14. Container

호프 2023. 12. 7. 15:40

Container

Disadvantages of Virtual Machines

Pros

  • Full autonomy(자율성)
  • Very secure
  • Lower costs
  • Used by all cloud providers for on demand server instances

Cons

  • Not very portable since size of VMs are large
  • Overhead

Container

Container

  • cut down VMs used to execute code in an isolated environment
  • portable and lightweight
  • fully packaged software with all dependencies included
  • can be used for development, training, and deployyment
  • easily share containers

Linux Containers

  • Run everywhere: regardless of kernel version / host distro
  • Run anything: if it can run on a Linux kernel, it can run
  • Lightweight VM
    • own process space / network interface
    • can run stuff as root (root권한으로 프로그램 실행 가능)
    • no device emulation (실제 하드웨어 디바이스 직접 사용)
  • Container == isolated processes
    • but share kernel wit host

What Makes Containers so Small?

  • Container == user space of OS
  • User space: all of the code in an OS that lives outside of the kernel

Docker

Docker


Docker

  • open source platform for building, deploying, and managing containerized applications

Docker Image

  • basis of a Docker container
  • represent a full application
  • template like a blueprint to create a running Docker container

Docker Container

  • standard unit in which the application service resides and executes

Docker Image = recipe, Docker Container = dish

 

Docker Engine

  • creates, ships and runs Docker containers

Registry Service (Docker Hub or Docker Trusted Registry)

  • cloud or server-based storage and distribution service for your images

 

Dockerfile

FROM alpine:latest
RUN apk update
RUN apk add nmap
ENTRYPOINT ["nmap"]
CMD ["localhost"]

FROM

  • tells the daemon, which base image to use while creating our new Docker image
  • you can use alpine, Ubuntu, Fedora, or any other OS image

RUN

  • instructs the Docker daemon to run the given commands while creating the image
  • Dockerfile can have multiple RUN commands, each of these RUN commands create a new layer in the image

ENTRYPOINT

  • let your container to run the same executable every time

CMD

  • set default commands and/or parameters when a docker container runs
  • CMD can be overwritten from the command line via the docker run command

 

Multiple Containers from Same Image

  • You can run multiple containers from the same image
    • Those containers are not necessarily all identical
    • You can instantiate it with different parameters using the CMD and therefore different containers will be different

 

Docker Image Layering

  • When execute the build command, the daemon reads the Dockerfile and creates a layer for every command

Image Layering

  • A application sandbox
    • Each container is based on an image that holds necessary config data
    • When you launch a container, a writable layer is added on top of the image
  • A static snapshot of the container configuration
    • Layer images are read-only
    • Each image depends on one or more parent images
  • An Image that has no parent
    • Platform images define the runtime environment, packages, and utilities necessary for containerized application to run

 

Docker Running Commands

docker --version
  • get version of Docker CLI
docker container ls
docker image les
  • list all containers & images
docker build -t ac215-d1 -f Dockerfile .
  • build an image based on a Dockerfile
  • -t ac215-d1: name of the image
  • -f Dockerfile .: name of the dockerfile and "." means look at the current working directory
docker run --rm --name ac215-d1 -ti --entrypoint /bin/bash ac215-d1
  • run a docker container using the image from Docker Hub
  • --rm: automatically clean up the container and remove the file system when the container exit
  • --name ac215-d1: name of the container
  • -ti: t - give us a terminal, i - interactive mode
  • --entrypoint /bin/bash: default command to execute on startup
  • ac215-d1: name of the image to use
docker system prune -a
  • exit from all containers and let us clear of all images
  • system: docker command for systems
  • prune -a: docker command option to remove all images not referenced by any containers

 

Why use Containers?

  • We need to handle many payloads meaning that we need different language supports
  • We need to deploy on many targets meaning that we need to deploy on different OSes
  • 👉 You can solve this problem by using containers

 

Monolithic Architecture: traditional model

Pros

  • Simple to develop, test, and scale

Cons

  • Difficult to maintain
  • One component failure will cause whole system fail
  • Difficult to create the patches for monolithic architecture
  • Adapting to new technologies is challenging
  • Take a long time to startup because all components needs to get started

👉 Today: Microservice Architecture

 

Software Development Workflow

Software Development Workflow without Container

 

Software Development Workflow with Container

Container Orchestration

Container Orchestration

Container Orchestration

  • underlying platform with a set of resources
  • orchestrate the connectivity btw the containers and automataically scale up and down based on the load
  • whole process of automatically deploying and managin containers

Kubernetes (K8s)

  • open-source system for automating deployment, scaling, and management of containerized applications
  • groups containers that make up an application int logical units for easy management and discovery
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