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Load Balancer Health Checks & Failover

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Health checks: knowing which backends are alive

A load balancer can only route to healthy backends — but how does it know which are healthy? Active health checks probe each backend on a schedule. Passive health checks watch real traffic for errors.

Active checks detect failures before clients do (no user sees the first failed request). Passive checks are faster to detect but a few real requests hit the bad backend first.

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