Nodes span machines

Because a node may be more than one machine, the ISP, or whoever owns the node, can offer a much more reliable service. The same goes for ASPs: it helps their service become more widely available.

If a machine within a node needs to shut down it can tell the netlets so they can close themselves down gracefully, perhaps moving to another location, perhaps on the same node. Meanwhile new netlets can still move onto the node without worry, because the node itself is still available. This is shown in Figure .

Figure: A netlet can take evasive action when it is told of a shutdown. In this case, while node 1 spans machines a-d, machine a, where the netlet is running, needs to close down for maintenance. Step 1: The netlet saves its state and sends its descriptor to another node. Step 2: The new node binds and initialises it. However, node 1 is still available, so the netlet could have chosen to relocate on the same node. The node is also still available for hosting others. Node 1 is still running on machines b-d.

 

Also, with several servers in the same node there are greater trust advantages for netlets which happen to be running on different servers of the same node. Suppose Harry has two netlets running on the same node. If one requests the ZFData service then the node can download it, and bind it to the netlet. If the second netlet then asks for the same service the node does not have to download it and perform the security checks again--because all that has already been done.