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Comment by tommi | Hacker News Reader

That can be avoided by altering the logic by which supernodes are queried. Not all nodes must try all supernodes.

Since it seems a good chunk of the super nodes went down, I imagine every running unconnected Skype instance is checking all of the super nodes it can find (or actively searching for them). Changing the logic at this point isn't really an option for them.

Well, even if we were to talk about this point, it actually might be. I have no knowledge of Skype architecture, so I'm totally guessing here. But, those unconnected Skype instances have to have some kind of directory of supernodes: either dynamic or static. If it's dynamic, that is from Skype's servers, it can be affected.

That's fair, but even if it is dynamic, I doubt it's checked on a regular basis; I doubt it's a scenario they've even considered before now. This would be on par with the DNS root servers changing and somehow letting everyone know about it on the fly.

I tend to disagree. Error handling exactly in such cases where you have to bring the network online from a complete halt or other catastrophe is at the very heart of the architecture of these systems. These scenarios should and are at the minds of the architects and coders.

That's a lot easier when it's your network. Skype is obviously designed to be used in "hostile" environments; super nodes are likely expected to go away and come back on a regular basis. Likewise, I don't think it's an unreasonable expectation that there will be a given number of nodes online at any given time.

If they all disappear, I doubt there's a contingency plan for that.

From the Skype's status update: "Our engineers are creating new ‘mega-supernodes’ as fast as they can, which should gradually return things to normal."

So they can inject new supernodes in to the system and clients will discover'em gradually. That kind of indicates that they have a mechanism not to DDOS the new mega-supernodes. It's a contingency plan. I fail to see what we are arguing here.

I'm just relaying my experience with P2P network design and with system-wide failures. I agree with you that gradual discovery is possible, but I doubt that's the best case scenario for them depending on how long it takes. They have the worst of both world: if it's slow, their users are going to be extremely frustrated, but if their clients are very quick to discover new nodes, the possibility of them getting swamped is still very real. The status update doesn't talk about their deployment strategy at all so I don't think we can make assumptions; either way has it's own potentially serious issues.

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