Ref: https://learn.cantrill.io/courses/1820301/lectures/41301611

• Summary
• Contents:

❗💡 For a more detailed introduction to containers, check the Docker Fundamentals Course

OS Virtualization Problems

• “OS virtualization” = correct, full-name for “virtualization”
  • i.e. Run multiple OSes on the same physical HW
  • ❗ Container virtualization (Containerization) does NOT virtualize OSes

• Disadvantages/problems with large deployments of OS virtualization:
  • 👎 OS often takes a lot of space in the VM
    • e.g. 4GB disk → usually 60-70% consumed by OS
  • 👎 Duplication of resources
    • multiple VMs on the same physical host can be running the same OS
  • 👎 OS consume lots of system resources = Heavy usage
    • every restart, stop & start implies manipulating the entire OS
• 💡 If we just want to use 6 apps in isolated environments, do we need 6 different OSes? Usually not! → Containers offer a better alternative

Containerization = Container Virtualization

• Most popular containerization SW = Docker
  • 💡 Many people treat containers and Docker as synonyms, but there's container SW alternatives like Podman
• Architecture: on top of HW, Host OS & Container Engine (Docker Engine)
  • Containers run on the engine

• 🔧 Container characteristics:

  • Isolated environments for apps & their RTE (libraries & dependencies)

    • Much of the same isolation as VMs

      💡 unless you need a full & isolated OS, give serious thought to containerization

  • ‼️ Containers don't run their own OS, they are a process of the Host OS!

    • Very lightweight, consume very little memory
    • Super fast to start & stop

  • Portable

    • Self-contained, always run as expected

  • Dense and tightly packed

    • Can run many, many more containers than VMs on the same physical HW

  • Host used for NWing & file I/O → container ports exposed to the host & beyond

• Application stacks can be multi-container
  • e.g. DB container + APP container working together

Image Anatomy

• 💡 An EC2 instance is a running copy of its EBS volumes (its virtual disks)
  • Boot Volume is used to launch a copy of an OS running in a virtualized environment
  • Similar concept for Docker images and containers