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	1...