How Containers Work: Overlayfs (jvns.ca)

Article summary

The article explains how overlay filesystems work, specifically in the context of Docker containers. It describes how overlayfs allows multiple layers of a filesystem to be combined, with a read-only lower layer and a writable upper layer. The author provides examples of how this works in practice, including creating and deleting files in the overlay filesystem. The article also touches on the use of other storage drivers, such as Btrfs, and their potential advantages and disadvantages.

Main themes

• overlay filesystems
• Docker containers
• storage drivers
• Btrfs
• filesystem layers
• container efficiency

What commenters say

• Using overlayfs is a key factor in making containers efficient in terms of hardware resources and developer time.
• Combining Docker with ZFS can be slow and painful, but using overlayfs on top of ZFS can be a viable alternative.
• Btrfs snapshots can be a good solution for managing multiple layers of a filesystem, but they can also lead to increased overhead and complexity.
• The use of overlayfs and other storage drivers is not unique to containers and can be applied to other use cases, such as building and testing software.
• Some users have found that using LVM snapshots can be a simpler and more efficient solution for managing filesystem layers.
• The choice of storage driver and filesystem layering strategy depends on the specific use case and requirements, and there is no one-size-fits-all solution.
• Using a ramfs or tmpfs for build directories can be a fast and efficient way to manage filesystem layers, but may not be suitable for large datasets.
• The implementation of containers and filesystem layering is not unique to Linux and can be found in other operating systems, such as BSD and Solaris.