thurbeen/domain-cloud-native

Cloud-Native Domain

Layer 3: Domain Constraints

Domain Constraints → Design Implications

| Domain Rule | Design Constraint | Rust Implication | |-------------|-------------------|------------------| | 12-Factor | Config from env | Environment-based config | | Observability | Metrics + traces | tracing + opentelemetry | | Health checks | Liveness/readiness | Dedicated endpoints | | Graceful shutdown | Clean termination | Signal handling | | Horizontal scale | Stateless design | No local state | | Container-friendly | Small binaries | Release optimization |

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Critical Constraints

Stateless Design

RULE: No local persistent state
WHY: Pods can be killed/rescheduled anytime
RUST: External state (Redis, DB), no static mut

Graceful Shutdown

RULE: Handle SIGTERM, drain connections
WHY: Zero-downtime deployments
RUST: tokio::signal + graceful shutdown

Observability

RULE: Every request must be traceable
WHY: Debugging distributed systems
RUST: tracing spans, opentelemetry export

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Trace Down ↓

From constraints to design (Layer 2):

"Need distributed tracing"
    ↓ m12-lifecycle: Span lifecycle
    ↓ tracing + opentelemetry

"Need graceful shutdown"
    ↓ m07-concurrency: Signal handling
    ↓ m12-lifecycle: Connection draining

"Need health checks"
    ↓ domain-web: HTTP endpoints
    ↓ m06-error-handling: Health status

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Key Crates

| Purpose | Crate | |---------|-------| | gRPC | tonic | | Kubernetes | kube, kube-runtime | | Docker | bollard | | Tracing | tracing, opentelemetry | | Metrics | prometheus, metrics | | Config | config, figment | | Health | HTTP endpoints |

Design Patterns

| Pattern | Purpose | Implementation | |---------|---------|----------------| | gRPC services | Service mesh | tonic + tower | | K8s operators | Custom resources | kube-runtime Controller | | Observability | Debugging | tracing + OTEL | | Health checks | Orchestration | /health, /ready | | Config | 12-factor | Env vars + secrets |

Code Pattern: Graceful Shutdown

use tokio::signal;

async fn run_server() -> anyhow::Result<()> {
    let app = Router::new()
        .route("/health", get(health))
        .route("/ready", get(ready));

    let addr = SocketAddr::from(([0, 0, 0, 0], 8080));

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .with_graceful_shutdown(shutdown_signal())
        .await?;

    Ok(())
}

async fn shutdown_signal() {
    signal::ctrl_c().await.expect("failed to listen for ctrl+c");
    tracing::info!("shutdown signal received");
}

Health Check Pattern

async fn health() -> StatusCode {
    StatusCode::OK
}

async fn ready(State(db): State<Arc<DbPool>>) -> StatusCode {
    match db.ping().await {
        Ok(_) => StatusCode::OK,
        Err(_) => StatusCode::SERVICE_UNAVAILABLE,
    }
}

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Common Mistakes

| Mistake | Domain Violation | Fix | |---------|-----------------|-----| | Local file state | Not stateless | External storage | | No SIGTERM handling | Hard kills | Graceful shutdown | | No tracing | Can't debug | tracing spans | | Static config | Not 12-factor | Env vars |

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Trace to Layer 1

| Constraint | Layer 2 Pattern | Layer 1 Implementation | |------------|-----------------|------------------------| | Stateless | External state | Arc<Client> for external | | Graceful shutdown | Signal handling | tokio::signal | | Tracing | Span lifecycle | tracing + OTEL | | Health checks | HTTP endpoints | Dedicated routes |

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Related Skills

| When | See | |------|-----| | Async patterns | m07-concurrency | | HTTP endpoints | domain-web | | Error handling | m13-domain-error | | Resource lifecycle | m12-lifecycle |