Länk - Feltoleranta system: svårt detektera sådant som fallerar "bara ibland"
It's not hard to have system B check that system A is on/off line, and step in if the latter is the case. But what happens when A is *mostly* or *sorta* online? Does system B check that ALL functionality done by A is being done appropriately? Almost never. And that's why, even in the best, most carefully designed, fully redundant high-availability systems, you never, ever see 100% uptime. It's just not possible to anticipate everything that can go wrong. So design a system that fails gracefully! That's what nature did.
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