On modern Linux systems, rkt now uses overlayfs by default when running application containers. This provides immense benefits to performance and efficiency: start times for large containers will be much faster, and multiple pods using the same images will consume less disk space and can share page cache entries.
If overlayfs is not supported on the host operating system, rkt gracefully degrades back to the previous behaviour of extracting each image at runtime - this behaviour can also be triggered with the new —no-overlay flag to rkt run.