This document discusses Docker container file systems. It explains that Docker images use a file system to maintain the file structure specified in the Dockerfile. Images are composed of read-only layers that build on one another to reduce storage needs. The default storage driver is Overlay2, which uses a copy-on-write strategy for efficiency. Volume mounts allow data to bypass the storage driver for better performance of write-heavy workloads. Different file systems and storage drivers are compared for their support in Docker.

1. A bit of docker container file
system
Deepak kumar
Fosscafe

2. Agenda
• File system
• Why it is needed
• Docker images

3. Pre-requisites
• On mind
• Docker basics idea in theory
• Basic hands-on of docker
• File system purpose
• On hand
• Laptop for trying out demo
• Internet connection

4. Known file systems in day-2-day life
• Ext3, ext4
• Linux
• FAT, NTFS
• Windows

5. When it comes to picture
• Docker is successful because of shipping container
• Shipping container is made possible by docker image
• Docker image uses file system
• To maintain file structure specified by user (Dockerfile)
• To share this file structure to multiple container instantiations

6. Docker image layer
• Read only
• Its enough to ship a
layer itself
• Upper layer maintains
diff from lower layer

7. Contd..

8. Docker image file system (overlay)

9. Demo
• Image layer size increment
• Extra size to container
• Image based share is efficient
• View docker image size and container size
• At beginning
• After edit of container

10. Docker commands
• docker info
• docker ps –s
• docker history
• docker system df

11. Layering in docker images by example

12. Demo
• Commit an existing container
• Run docker history on new image
• Check the parent image ID and new image ID position

13. More about overlays
• Now default is overlay filesystem (overlay2)
• Earlier docker uses aufs
• You can check it using ‘docker info’ command
• Look for ‘Storage Driver’ option

14. Why overlay is default
• The copy-on-write (CoW) strategy
• Page Caching

15. Change storage driver to overlay
• Instruct in /etc/docker/daemon.json
• Change the option to overlay2
• Restart docker

16. When not to use writable layer
• write-heavy workloads
• Use –v option and mount the volume
• Use block level storage driver

17. Handling data volume (-v option)
• Data volumes are not controlled by the storage driver
• Read/Write bypass storage driver
• Operate at native host speed
• Data volume survives on deletion of container

18. Other file systems
• Vfs, AUFS, OVERLAY, Overlay2
• aufs, overlay, and overlay2 all operate at the file level rather than the
block level.
• Block-level storage drivers such as devicemapper, btrfs, and zfs

19. Backing filesystem support matrix

20. • https://www.youtube.com/watch?v=24bKqcWVGgc
• For File system
• https://www.youtube.com/watch?v=vlS5EiapiII
• Creating Effective Docker Images