# Reliability and Bonus Quest Overview

## Goal

This section ensures the service fails safely, recovers predictably, and remains diagnosable under stress or unexpected behavior.

## Reliability pillars implemented

* Error contract stability (`400/404/422/500` with JSON responses)
* Global exception handling to prevent sensitive error leakage
* DB connection pool hardening (`pool_pre_ping`, bounded pool/overflow)
* Health endpoint and optional Prometheus request telemetry
* Redis cache with graceful fallback behavior
* Background event logging to keep request paths responsive
* Dedicated one-time startup initialization service (`app-init`)
* Container restart policies and healthchecks

## Why this matters for new team members

When you join the project, reliability docs tell you two critical things quickly:

1. What the system guarantees under failure.
2. How to diagnose and recover when those guarantees are breached.

## Reliability architecture at a glance

* API error normalization in `app/__init__.py`
* startup initialization and observability setup in `run.py`
* logging and metrics helpers in `app/observability.py`
* DB resilience settings in `app/database.py`
* cache reliability helpers in `app/cache.py`

## Related pages

* `error-handling-contract.md`
* `resilience-and-recovery.md`
* `bonus-quest-report.md`
* `diagrams.md`