2 ms·

Fun facts about availability: 1) the more nodes, the higher probability of failure, 2) the more load, the higher probability of failure, 3) complex logic and/o

Fun facts about availability: 1) the more nodes, the higher probability of failure, 2) the more load, the higher probability of failure, 3) complex logic and/or nodes that aren't tested frequently have a higher probability of failure Basically, every person who has claimed "X is easy, I do it for my personal use and it's fine with one giant node, don't need HA" is true (for them) because it's literally less likely to fail. But if they had more load they'd see more failures, and probability doesn't mean they won't encounter the random failures that are much harder to recover when there's no backup system. HA means you're going to have more failure, which means more work to keep it running. But it's necessary work if total system failure is unacceptable. Two engines in an airplane is twice the maintenance, but it's better than the only engine conking out mid-flight.

rospaya 4y ago
> 1) the more nodes, the higher probability of failure I may be misreading your comment, but how is this true?
- lhoff 4y ago
  If you have one node with the probability of x% that it fails within a year and you add a second one with the same probability to fail the total pobability that one of the two nodes fail within a year goes up.
  - deleted 4y ago
    [deleted]
- macintux 4y ago
  Not OP, but two things I’ve found to be true: * the more complex the configuration required to provide high availability, the more likely something will go wrong and reduce availability * the more nodes you have, the more likely one of them will fail. Whether that reduces availability typically depends on the failure mode and control layer. For an example of the latter, with the distributed database Riak (and I imagine others as well) if a server is starting to fail (corrupt disk, bad network card, etc) you’re in a much better place if it stops working entirely. A gradual node failure is much much worse.
- notacoward 4y ago
  This is one of the classic problems of talking about HA: making it clear which "failure" or "availability" you mean at any given moment. In the particular quoted sentence, "failure" refers to component failure even though the "availability" in HA means system availability. The goal of HA design is to make a system that becomes more available as components are added instead of less (as you seem to expect). Redundancy, internal monitoring, and failover are the tools of the trade. What you should end up with is a system more like two chains holding up an object instead of one chain twice as long.
marcosdumay 4y ago
HA has a very sweet spot at the place where "the system is down at 3AM and must be fixed RIGHT NOW!" do not happen, but the complexity isn't increased enough for it to generate much ongoing work. Anybody bellow that spot is just begging for being taken out by random at the worst possible times.

rospaya 4y ago

> 1) the more nodes, the higher probability of failure I may be misreading your comment, but how is this true?

lhoff 4y ago
If you have one node with the probability of x% that it fails within a year and you add a second one with the same probability to fail the total pobability that one of the two nodes fail within a year goes up.
- deleted 4y ago
  [deleted]
macintux 4y ago
Not OP, but two things I’ve found to be true: * the more complex the configuration required to provide high availability, the more likely something will go wrong and reduce availability * the more nodes you have, the more likely one of them will fail. Whether that reduces availability typically depends on the failure mode and control layer. For an example of the latter, with the distributed database Riak (and I imagine others as well) if a server is starting to fail (corrupt disk, bad network card, etc) you’re in a much better place if it stops working entirely. A gradual node failure is much much worse.
notacoward 4y ago
This is one of the classic problems of talking about HA: making it clear which "failure" or "availability" you mean at any given moment. In the particular quoted sentence, "failure" refers to component failure even though the "availability" in HA means system availability. The goal of HA design is to make a system that becomes more available as components are added instead of less (as you seem to expect). Redundancy, internal monitoring, and failover are the tools of the trade. What you should end up with is a system more like two chains holding up an object instead of one chain twice as long.

marcosdumay 4y ago

HA has a very sweet spot at the place where "the system is down at 3AM and must be fixed RIGHT NOW!" do not happen, but the complexity isn't increased enough for it to generate much ongoing work. Anybody bellow that spot is just begging for being taken out by random at the worst possible times.