Containerization 101

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

❗💡 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

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