This tag represents the "second" algorithm that Chord describes.
The first algorithm doesn't hold up in the face of concurrent node joins because it is too aggressive in the way it maintains the finger table entries. The successive algorithm (tagged by this release) "fixes" that by periodically updating the successor and predecessor pointers (and finger tables) of a node.
This milestone is important because this algorithm handles failures. To check this, shut down a container on the Chord network and observe the rest of the network adjust accordingly.