OCI Image Format Specification

• Image standard specification
• Tool to manage OCIs: runc https://github.com/opencontainers/runc

Layered architecture

• Container Layer: Read-Write layer that a system is running
• Image Layer: Read-Only layer pre-built

• If a file from the image layer is modified, it's actually copied and modified (copy-on-write)
• The Container Layer is lost after the pod has been terminated
• The container image is a set of binary layers (similar to git commits, but to binary files)

Overlay2

• It's the union filesystem mounted from the image into the container
• It unifies all the layers from the image