Ref: https://learn.cantrill.io/courses/docker-fundamentals/lectures/44151202

YouTube: https://www.youtube.com/watch?v=BKNnQPyqJvc

DEMO: https://learn.cantrill.io/courses/docker-fundamentals/lectures/44151206

DEMO-YouTube: https://www.youtube.com/watch?v=oW97xGNYNkM

DEMO-GitHub: https://github.com/acantril/docker-fundamentals/blob/main/Working-with-existing-docker-images.md

• Summary
• Contents:

Docker Images

• 🔧 Immutable, read-only templates
  • changing an image implies creating a new image
• Structure: collection of independent file system layers
  • Differential layers → each layer contains only the differences from layer below
  • ❗ Layers are independent and can be reused
    • docker pull only pulls missing layers → avoids unnecessary uploads & downloads
  • Image is presented as a single file to the outside, even if inside there's layers
• Docker Images Diagram

Docker Containers

• 🔧 An instance of a Docker image which can run
• Containers add a writable layer to the image template
  • Any data changes that happen at runtime are stored in this layer
    • image layers remain unaltered during runtime
  • This layer implies a performance hit when container runs
  • ❗ Writable layer is linked to container's lifecycle
    • persists when container is stopped, but not when it's deleted
  • The union file system overlaps all layers as a single entity
    • all data is tightly coupled with the host → data cannot be easily moved
• Docker Containers Diagram

Additional useful/basic commands

• docker inspect <ID> - show metadata of Docker object
  • Docker object can be image, container, volume…