Everybody knows single points of failure are bad. That's not the part anyone actually needs convincing of. The part that's genuinely hard is finding them, because they're rarely sitting somewhere obvious with a sign on them — they're usually hiding one or two layers underneath something that looks perfectly redundant on the surface, and finding them requires a specific kind of stubborn, methodical tracing that most network reviews don't actually do.
My honest take: most networks that call themselves redundant have at least one genuine single point of failure nobody's found yet, hiding not because anyone was careless, but because finding it requires actually tracing every dependency rather than trusting that redundant-looking components are genuinely independent of each other.
Start by Asking "What Else Does This Depend On"
The most common way a single point of failure hides is through a shared dependency underneath two things that look independent. Two internet connections from two different providers sounds genuinely redundant — until you find out both providers' physical lines run through the same conduit under the same street, and a single construction accident takes out both simultaneously. The redundancy was real at the logical level and completely absent at the physical level, and nobody found that out until they went looking specifically for it.
The habit worth building: for anything you believe is redundant, keep asking "and what does that depend on" until you hit something that's genuinely, physically independent, not just administratively labeled as a separate thing.
Power Is the Classic Overlooked Single Point of Failure
Redundant servers, redundant network paths, redundant everything — running off a single power circuit or a single UPS. This is one of the most common findings in real network reviews, and it's genuinely embarrassing once found, because everyone assumed the technical redundancy meant something was covered when the actual vulnerability was sitting one layer down in the electrical infrastructure nobody thought to check.
DNS Deserves Its Own Dedicated Hunt
DNS failure can take down an entire, otherwise perfectly healthy network, because everything depends on being able to resolve names to addresses before any of the rest of the redundancy even gets a chance to matter. DNS redundancy needs to be checked as its own specific item, not assumed to inherit whatever general redundancy exists elsewhere in the network, because it's foundational enough that a gap here undermines every other redundant system you've built.
The Human Single Point of Failure Nobody Wants to Talk About
This one's uncomfortable and worth saying anyway: if the one person who genuinely understands how a specific piece of your network is configured left tomorrow, how long would it take everyone else to safely operate or fix it? That's a real single point of failure too, and it's exactly as dangerous as an unredundant switch, just harder to put on an architecture diagram. Documentation is the fix, and it's consistently the fix that gets skipped because it doesn't feel as urgent as the technical work.
Testing Is How You Actually Find the Ones You Missed
Reviewing a diagram finds the single points of failure someone thought to draw accurately. Actually testing — forcing a specific component offline and watching what genuinely happens — finds the ones that weren't obvious from the diagram at all, including the shared conduit, the shared power circuit, the dependency nobody remembered existed until it suddenly mattered.
What This Actually Requires
- Tracing every "redundant" component down to genuine physical and logical independence, not stopping once something looks administratively separate
- Checking power infrastructure specifically, since it's one of the most common places redundancy quietly fails underneath otherwise-redundant systems
- Treating DNS as its own dedicated redundancy item, not an inherited assumption
- Recognizing concentrated human knowledge as a genuine single point of failure, addressed through real documentation
- Actually testing by forcing components offline, not just reviewing configuration and trusting it
The Actual Point
Single points of failure survive not because anyone's careless, but because finding them requires a specific, patient discipline most reviews skip in favor of confirming things look redundant on paper. The networks that genuinely eliminate them aren't the ones with the most redundant-looking diagrams — they're the ones who kept asking "what else does this depend on" until they ran out of layers to check.
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