Scheduling Service — Failure Modes

Status: populated Owner: TBD Last updated: 2026-04-17 Companion: Service Template

1. Failure Catalog

ID	Failure	User Impact	Detection	Mitigation
FM-SCHED-01	PostgreSQL unavailable	All scheduling operations fail	Healthcheck readiness probe; alert	Replica promotion; retry on reconnect
FM-SCHED-02	NATS unavailable	Bookings persist but no events published	Outbox lag metric alert	Outbox relay retries when NATS recovers
FM-SCHED-03	Slot reservation race condition	Two users book same slot simultaneously	Unique index constraint violation → one gets 409	Atomic slot status update via DB transaction + unique index
FM-SCHED-04	Reminder dispatch failure	Patient misses appointment reminder	Reminder failure rate alert	Async retry up to 3×; dead-letter queue; patient can check portal
FM-SCHED-05	registration-service events delayed	Deceased patient appointments not auto-cancelled promptly	Monitoring on event lag	Eventual consistency; staff UI shows deceased flag; manual cancellation
FM-SCHED-06	HL7 SIU inbound parse failure	External system appointment not reflected	Dead-letter queue alert	Dead-letter queue; manual reprocessing runbook
FM-SCHED-07	Clock skew causing timezone rendering error	Appointments displayed at wrong time	User report; monitoring on slot/appointment time deltas	Timezone stored as IANA string; all timestamps UTC; client renders using schedule timezone
FM-SCHED-08	Waitlist auto-fill event published but patient not reachable	Patient misses waitlist offer	Reminder dispatch failure metric	Retry reminder; SLA window for patient response before auto-expiry
FM-SCHED-09	Redis unavailable (reminder queue)	Scheduled reminders not dispatched	Redis health alert	Reminders delayed; catch-up dispatch on Redis restore