High Availability and Failover: RPO/RTO, Listeners, Patroni and Making the Application Survive Failover
An application survives failover only with idempotent writes and a retry that waits for the failover; an async replica is not lossless. In the lab an async replica lost 50 orders; the default EF Core retry didn't retry "No suitable host was found" and 98 orders failed, while a widened strategy and Host Recheck Seconds=1 gave zero errors and zero duplicates. RPO/RTO, HA and DR, AG listeners, Patroni and SqlClient ConnectRetryCount.
14 Nov 2026
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12 min
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15
