Problem Statement
When a critical component in a system fails, the entire system can stop working if there is no backup or alternative path. This causes downtime and loss of service, which can be costly and frustrating for users.
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Single point of failure identification in HLD - System Design Guide
Solution
Identify components that, if they fail, cause the whole system to fail. Then design redundancy or failover mechanisms for these components to ensure the system continues working even if one part breaks.
Architecture
Client
→Single Server
Database
Database
This diagram shows a simple system where the client depends on a single server, which in turn depends on a single database. Both server and database are single points of failure.
Trade-offs
✓ Pros
Helps find critical failure points before they cause outages.
Enables targeted improvements to system reliability.
Supports planning for redundancy and failover.
✗ Cons
Can be time-consuming for complex systems with many components.
May require detailed knowledge of system internals.
Does not by itself fix failures, only identifies risks.
Use during system design or before deployment, especially for systems with high availability requirements or complex architectures.
Not necessary for very simple systems with minimal components or when downtime has no significant impact.
Real World Examples
Netflix
Identified single points of failure in their streaming infrastructure and introduced multi-region redundancy to avoid outages.
Amazon
Analyzed critical components in their e-commerce platform to ensure no single server or database failure could stop order processing.
Uber
Mapped dependencies in their ride matching system to eliminate single points of failure and maintain service during component failures.
Alternatives
Redundancy Design
Focuses on adding backup components rather than just identifying failure points.
Use when:
After single points of failure are identified and you want to improve system resilience.
Failover Mechanism
Implements automatic switching to backup components upon failure.
Use when:
When you need automatic recovery from failures identified in the system.
Summary
Single point of failure identification finds components whose failure stops the whole system.
It helps teams plan redundancy and failover to improve system availability.
This process is essential for designing reliable systems that serve users without interruption.