Content Addressable Network - Node Departing

Node Departing

To handle a node departing, the CAN must i) identify a node is departing, ii) have the departing node's zone merged or taken-over by a neighboring node, and iii) update the routing tables across the network.

Detecting a node's departure can be done, for instance, via heartbeat messages that periodically broadcast routing table information between neighbors. After a predetermined period of silence from a neighbor, that neighboring node is determined as failed and is considered a departing node. Alternatively, a node that is willingly departing may broadcast such a notice to its neighbors.

After a departing node is identified, its zone must be either merged or taken-over. First the departed node's zone is analyzed to determine whether a neighboring node's zone can merge with the departed node's zone to form a valid zone. For example, a zone in a 2d coordinate space must be either a square or rectangle and cannot be L-shaped. The validation test may cycle through all neighboring zones to determine if a successful merge can occur. If one of the potential merges is deemed a valid merge, the zones are then merged. If none of the potential merges are deemed valid, then the neighboring node with the smallest zone takes over control of the departing node's zone. After a take-over, the take-over node may periodically attempt to merge its additionally controlled zones with respective neighboring zones.

If the merge is successful, routing tables of neighboring zones' nodes are updated to reflect the merge. The network will see the subsection of the overlay network as one, single zone after a merge and treat all routing processing with this mindset. To effectuate a take-over, the take-over node updates neighboring zones' nodes' routing tables, so that requests to either zone resolve to the take-over node. And, as such, the network still sees the subsection of the overlay network as two separate zones and treats all routing processing with this mindset.