Startup uptime monitoring requires four separate health signals for reliability

A technical guide outlines four essential signals for monitoring startup uptime: an external probe, an internal healthcheck endpoint, a cron deadline, and durable per-run cost-and-latency records. The architecture emphasizes independence from the monitored system, ensuring monitoring components do not share the same failure domain. It stresses compatibility during rollbacks, where old and new application versions must both emit valid records without requiring database changes. Each signal covers different failure boundaries, with no single green light considered sufficient for system reliability. The approach prioritizes bounded record storage in Postgres and additive schema changes to maintain stability.