This chapter covers fault tolerance vs availability concepts. AZ-900 tests under 1.5.
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A simple way to picture Fault Tolerance vs High Availability
A bridge is designed to stay upright even with traffic loss (fault tolerance) vs. a bridge that fails immediately if one cable breaks (no tolerance). Fault tolerance is the design philosophy.
Fault tolerance is the ability to handle component failures without total failure. It's related to availability but distinct: availability is the percentage of time working; fault tolerance is the ability to survive failures.
Design for failures
Assume components will fail; design around it.
Add redundancy
Multiple instances so one failure doesn't stop the system.
Monitor and heal
Detect failures and automatically restart failed instances.
A system with fault tolerance continues working even if individual servers fail, automatically restarting failed ones.
Objective 1.5 expects understanding that fault tolerance and availability are related but distinct.
Fault tolerance handles failures without total failure.
Related to but distinct from availability.
Achieved through redundancy and monitoring.
The ability of a system to handle component failures without experiencing a total system failure, achieved through redundancy and automatic recovery.
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