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//! Observability guide for tower-resilience.
//!
//! This module provides comprehensive guidance on metrics, tracing, and monitoring
//! for all resilience patterns.
pub mod metrics {
//! # Metrics Guide
//!
//! All resilience patterns support optional Prometheus-compatible metrics via the `metrics` feature.
//!
//! ## Enabling Metrics
//!
//! ```toml
//! [dependencies]
//! tower-resilience = { version = "0.3", features = ["circuitbreaker", "metrics"] }
//! metrics = "0.24"
//! metrics-exporter-prometheus = "0.16"
//! ```
//!
//! ## Instance Naming
//!
//! **Always name your instances** to distinguish metrics from multiple patterns:
//!
//! ```rust,ignore
//! // Multiple circuit breakers with different names
//! let user_cb = CircuitBreakerLayer::builder()
//! .name("user-service") // ← Instance name
//! .build();
//!
//! let payment_cb = CircuitBreakerLayer::builder()
//! .name("payment-service")
//! .build();
//! ```
//!
//! Metrics will include the instance name as a label:
//! ```text
//! circuitbreaker_calls_total{circuitbreaker="user-service",outcome="success"} 150
//! circuitbreaker_calls_total{circuitbreaker="payment-service",outcome="success"} 89
//! ```
//!
//! ## Available Metrics by Pattern
//!
//! ### Circuit Breaker
//!
//! - `circuitbreaker_calls_total{circuitbreaker, outcome}` - Total calls (success/failure/rejected)
//! - `circuitbreaker_transitions_total{circuitbreaker, from, to}` - State transitions
//! - `circuitbreaker_state{circuitbreaker, state}` - Current state gauge
//! - `circuitbreaker_slow_calls_total{circuitbreaker}` - Slow call detections
//! - `circuitbreaker_call_duration_seconds{circuitbreaker}` - Call duration histogram
//!
//! ### Bulkhead
//!
//! - `bulkhead_calls_permitted_total{bulkhead}` - Calls that acquired permits
//! - `bulkhead_calls_rejected_total{bulkhead}` - Calls rejected (no permits)
//! - `bulkhead_calls_finished_total{bulkhead}` - Successfully completed calls
//! - `bulkhead_calls_failed_total{bulkhead}` - Failed calls
//! - `bulkhead_concurrent_calls{bulkhead}` - Current concurrency gauge
//! - `bulkhead_wait_duration_seconds{bulkhead}` - Wait time histogram
//! - `bulkhead_call_duration_seconds{bulkhead}` - Call duration histogram
//!
//! ### Retry
//!
//! - `retry_calls_total{retry, result}` - Total retry operations (success/exhausted)
//! - `retry_attempts_total{retry}` - Individual retry attempts
//! - `retry_attempts{retry}` - Attempts per call histogram
//!
//! ### Rate Limiter
//!
//! - `ratelimiter_calls_total{ratelimiter, result}` - Calls (permitted/rejected)
//! - `ratelimiter_wait_duration_seconds{ratelimiter}` - Permit wait time histogram
//!
//! ### Time Limiter
//!
//! - `timelimiter_calls_total{timelimiter, result}` - Calls (success/error/timeout)
//! - `timelimiter_call_duration_seconds{timelimiter}` - Call duration histogram
//!
//! ### Cache
//!
//! - `cache_requests_total{cache, result}` - Cache requests (hit/miss)
//! - `cache_evictions_total{cache}` - Cache evictions
//! - `cache_size{cache}` - Current cache size gauge
//!
//! ## Example Prometheus Queries
//!
//! ```promql
//! # Circuit breaker failure rate
//! rate(circuitbreaker_calls_total{outcome="failure"}[5m])
//! /
//! rate(circuitbreaker_calls_total[5m]) * 100
//!
//! # Bulkhead rejection percentage
//! rate(bulkhead_calls_rejected_total[5m])
//! /
//! (rate(bulkhead_calls_permitted_total[5m]) + rate(bulkhead_calls_rejected_total[5m]))
//! * 100
//!
//! # Average retry attempts per call
//! rate(retry_attempts_total[5m]) / rate(retry_calls_total[5m])
//!
//! # Cache hit rate
//! rate(cache_requests_total{result="hit"}[5m])
//! /
//! rate(cache_requests_total[5m]) * 100
//!
//! # P95 call latency
//! histogram_quantile(0.95,
//! rate(circuitbreaker_call_duration_seconds_bucket[5m])
//! )
//! ```
//!
//! ## Alert Examples
//!
//! ```yaml
//! # Circuit breaker opened
//! - alert: CircuitBreakerOpen
//! expr: circuitbreaker_state{state="Open"} == 1
//! for: 1m
//!
//! # High failure rate
//! - alert: HighFailureRate
//! expr: |
//! rate(circuitbreaker_calls_total{outcome="failure"}[5m])
//! / rate(circuitbreaker_calls_total[5m]) > 0.1
//! for: 5m
//!
//! # Bulkhead saturation
//! - alert: BulkheadSaturated
//! expr: |
//! rate(bulkhead_calls_rejected_total[5m])
//! / (rate(bulkhead_calls_permitted_total[5m])
//! + rate(bulkhead_calls_rejected_total[5m])) > 0.5
//! for: 5m
//! ```
}
pub mod tracing_guide {
//! # Tracing Guide
//!
//! Enable detailed logging with the `tracing` feature:
//!
//! ```toml
//! [dependencies]
//! tower-resilience = { version = "0.3", features = ["circuitbreaker", "tracing"] }
//! tracing-subscriber = "0.3"
//! ```
//!
//! Each pattern emits structured logs at key decision points:
//!
//! ```text
//! DEBUG circuitbreaker: Call succeeded within timeout duration_ms=45 circuitbreaker="user-service"
//! WARN circuitbreaker: Circuit opened from=Closed to=Open circuitbreaker="payment-service"
//! INFO retry: Request succeeded after retries attempts=3 retry="api-client"
//! DEBUG bulkhead: Permit acquired after waiting wait_ms=12 bulkhead="db-pool"
//! ```
}
pub mod events {
//! # Event System Guide
//!
//! All patterns provide an event system for custom observability:
//!
//! ```rust,ignore
//! let circuit_breaker = CircuitBreakerLayer::builder()
//! .on_state_transition(|from, to| {
//! println!("Circuit transitioned from {:?} to {:?}", from, to);
//! })
//! .on_call_rejected(|| {
//! // Custom handling, e.g., send to alerting system
//! })
//! .build();
//! ```
//!
//! See individual pattern documentation for available event listeners.
}