load-balancer.kdl

// Example: Load Balancer Configuration
//
// Traffic distribution across multiple backends with:
// - Multiple load balancing algorithms
// - Weighted round-robin
// - Health checks with ejection
// - Circuit breakers
// - Connection draining

system {
    worker-threads 0
    max-connections 20000
    graceful-shutdown-timeout-secs 60
}

listeners {
    listener "http" {
        address "0.0.0.0:8080"
        protocol "http"
        request-timeout-secs 60
    }
}

// =============================================================================
// Routes
// =============================================================================
routes {
    // Main application route
    route "app" {
        priority "normal"

        matches {
            path-prefix "/"
        }

        upstream "app-cluster"

        circuit-breaker {
            failure-threshold 5
            success-threshold 2
            timeout-seconds 60
            half-open-max-requests 3
        }

        retry-policy {
            max-attempts 3
            timeout-ms 10000
            backoff-base-ms 100
            retryable-status-codes 502 503 504
        }

        policies {
            timeout-secs 30
            failure-mode "open"
        }
    }

    // Health check
    route "health" {
        priority "critical"

        matches {
            path "/health"
        }

        builtin-handler "health"
    }

    // Upstream status endpoint
    route "upstream-status" {
        priority "critical"

        matches {
            path "/upstream-status"
        }

        builtin-handler "health"
    }
}

// =============================================================================
// Upstreams with different load balancing strategies
// =============================================================================
upstreams {
    // Primary cluster with weighted round-robin
    upstream "app-cluster" {
        // Weights determine traffic distribution
        target "10.0.1.10:3000" weight=100
        target "10.0.1.11:3000" weight=100
        target "10.0.1.12:3000" weight=100
        target "10.0.1.13:3000" weight=50   // Lower capacity node
        target "10.0.1.14:3000" weight=50   // Lower capacity node

        load-balancing "weighted-round-robin"

        health-check {
            type "http" {
                path "/health"
                expected-status 200
            }
            interval-secs 5
            timeout-secs 3
            healthy-threshold 2
            unhealthy-threshold 3
        }

        connection-pool {
            max-connections 100
            max-idle 20
            idle-timeout-secs 60
        }

        timeouts {
            connect-secs 5
            request-secs 30
            read-secs 30
        }
    }

    // Least connections - good for varying request durations
    upstream "app-least-conn" {
        target "10.0.2.10:3000" weight=1
        target "10.0.2.11:3000" weight=1
        target "10.0.2.12:3000" weight=1

        load-balancing "least-connections"

        health-check {
            type "http" {
                path "/health"
            }
            interval-secs 5
            timeout-secs 3
            healthy-threshold 2
            unhealthy-threshold 3
        }
    }

    // IP hash - session affinity
    upstream "app-sticky" {
        target "10.0.3.10:3000" weight=1
        target "10.0.3.11:3000" weight=1

        load-balancing "ip-hash"

        health-check {
            type "http" {
                path "/health"
            }
            interval-secs 10
            timeout-secs 5
            healthy-threshold 2
            unhealthy-threshold 3
        }
    }
}

// =============================================================================
// Blue-Green Deployment Example
// =============================================================================
// To switch traffic between blue and green:
// 1. Update the route to point to the other upstream
// 2. Hot-reload the configuration

// Blue environment
// upstream "app-blue" {
//     target "10.0.10.10:3000" weight=1
//     target "10.0.10.11:3000" weight=1
//     load-balancing "round-robin"
// }

// Green environment
// upstream "app-green" {
//     target "10.0.20.10:3000" weight=1
//     target "10.0.20.11:3000" weight=1
//     load-balancing "round-robin"
// }

// =============================================================================
// Canary Deployment Example
// =============================================================================
// upstream "app-canary" {
//     // Stable (90% traffic)
//     target "10.0.1.10:3000" weight=90
//     target "10.0.1.11:3000" weight=90
//     // Canary (10% traffic)
//     target "10.0.2.10:3000" weight=10
//
//     load-balancing "weighted-round-robin"
// }

// =============================================================================
// Observability
// =============================================================================
observability {
    metrics {
        enabled #true
        address "0.0.0.0:9090"
        path "/metrics"
        // Key metrics:
        // - zentinel_upstream_health (per target)
        // - zentinel_upstream_requests_total
        // - zentinel_upstream_latency_seconds
        // - zentinel_circuit_breaker_state
    }

    logging {
        level "info"
        format "json"
    }
}

limits {
    max-header-size-bytes 8192
    max-header-count 100
    max-body-size-bytes 10485760
}