What is Single Point of Failure (SPOF) in System Design?

Learn what a Single Point of Failure (SPOF) is, why it matters in system design, and how to eliminate it for more reliable systems.

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Hello friends, Single point failure is not just an important topic for System design interviews, its also technique in software development to design a System which can be used for mission critical purpose on real world.

For developers, avoiding Single point of failure is crucial while designing application to improve resiliency and avaibility of application.

You surely don’t want your system to die in the middle of a trading day.

Imagine Amazon going down on Prime day or Black Friday, how much business and reputation lose that will be? That’s why its important to know what is Single point failure and how to avoid it.

I have worked on all kind of monolith, microservices, and distributed system and they always have some kind of center point like a database server where all the configuration of services are stored or an auth server where all request should go before any processing.

These are the places which must have proper backup like a secondary instance which is replicated in real time or hot-hot setup where both instance have same data and requests are routed using load balancing algorithms.

In the past, I have talked about common system design questions like API Gateway vs Load Balancer and Horizontal vs Vertical Scaling, Forward proxy vs reverse proxy as well common System Design problems and in this article I have teamed up with

Hayk

to teach you Single Point of Failure in System design.

It's also one of the essential System design topics for interview and you must prepare it well.

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What is a Single Point of Failure?

A single point of failure (SPOF) is a part of a system that, when it fails, brings the entire system down.

In simple terms, it’s any component that could cause the whole system to fail if it stops working.

For example, if you have a web application where the database is on a single server.

If that server goes down, your whole application becomes unavailable, impacting user experience and potentially leading to data loss.

Here are a couple of examples of single point of failures: