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What is Single point of failure (SPOF)?

A point where a stop in just that one place stops the whole system. Besides equipment that is not made redundant, a shared power supply, a network line or a configuration file can also be a single point of failure. In reliability design, finding single points of failure and making them redundant is a basic step.

Japanese name: 単一障害点(SPOF)

Single point of failure (SPOF) appears in 1 practice question across 1 topic, including System Architecture and Reliability.

Field: System Architecture and Reliability

Try it: questions about Single point of failure (SPOF)

A system has two redundant load balancers, three web servers behind them, and a single database server used by all the web servers. Among the devices listed here, which is a single point of failure (a point whose stopping stops the whole system)?

  1. AThe load balancers
  2. BThe web servers
  3. CThe database server
Show answer and explanation

Answer: C. The database server

A single point of failure (SPOF) is a point where a stop in just that one place stops the whole system. The load balancers are made redundant with two units, and there are three web servers and the load balancers can remove a failed server from distribution, so processing continues even if any one of them stops. There is only one database server and every web server uses it, so if it stops, the whole system stops. Making the database server redundant too, for example with a cluster configuration, removes this single point of failure.

Single point of failure (SPOF) in the explanations

Questions that mention Single point of failure (SPOF) (1)

  1. A system has two redundant load balancers, three web servers behind them, and a single database server used by all the web servers. Among the devices listed here, which is a single point of failure (a point whose stopping stops the whole system)?

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Related terms

Load balancer Differential backup Dual system Duplex system Fail-safe Fail-soft Fault tolerance Fool-proof Hot standby Incremental backup

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