Availability Patterns: Failover & Redundancy
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- -Compare active-passive and active-active failover
Active-Passive Failover
One region (or replica) actively serves traffic; a standby sits idle, ready to take over if the primary fails. Simple to reason about, but wasteful (the standby's capacity sits unused most of the time), and failover itself takes time, meaning a real (if brief) outage window.
Active-Active
Multiple regions serve production traffic simultaneously, so no capacity sits idle and losing one region just means the others absorb its share. The cost is real: now two regions can both accept writes to the same data at the same time, and something has to resolve the conflict when they disagree.
Active-active: both regions serve live traffic and replicate to each other.
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Level 26: Distributed Cache exercises these consistency trade-offs directly.