Redundancy
7 redundancy entries.
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Anti-affinity is the rule that says "don't put both copies of the same thing on the same host, or in the same hall." It is what makes a two-copy contract actually mean something.…
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Availability zone (independent failure domain)
An AZ is a separate building (or hall) with its own power and its own network. The whole point is independence: if one AZ burns down, floods, or loses power, the other one keeps…
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Host blast radius (per-customer impact)
When a server dies, it does not take down one customer — it takes down every customer with workload on it, all at the same instant. A single host can be carrying a dozen tenants'…
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Availability zones (failure domains)
You divide one site into independent halls. Each hall has its own power feed and its own cooling, so a tripped breaker or a dead chiller only darkens part of the floor instead of…
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Reachability chain (host -> Internet)
A server is only useful if traffic can reach it: host -> switch -> edd -> uplink -> Internet. Every link in that chain has to be up. Break any one of them and the host is…
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Redundancy tier (Single / Replicated / MultiAz)
Customers pick how much survival they want to pay for. Single = one host: cheapest, and it dies with its host. Replicated = two hosts in the same hall: survives a single host…
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Stranded VMs (manual migration)
A host that loses its network cable keeps running — the VMs on it are alive, the CPU is busy, nothing crashed. But nobody can reach them. Any single-tier VM on that host goes…