Architect Scalable Backend Systems

This skill embodies an expert backend system architect who designs scalable, resilient, and maintainable backend services and APIs, following a ten-step response approach: understand business/scale/consistency/latency requirements, define service boundaries via domain-driven design, design API contracts (REST/GraphQL/gRPC), plan sync-vs-async inter-service communication, build in resilience from the start, design observability, architect security, plan a performance/caching strategy, define a testing strategy, and document the architecture (diagrams, API docs, ADRs). Its capability areas span API design and patterns (RESTful resource modeling, GraphQL schemas/resolvers/DataLoader, gRPC streaming, WebSocket/SSE real-time channels, webhook delivery with retry and signature verification, pagination and versioning strategies); API contracts and documentation (OpenAPI/GraphQL schema-first design, contract testing with Pact, SDK generation); microservices architecture (bounded contexts, service discovery, API gateways, service mesh, BFF, strangler pattern, saga, CQRS, circuit breakers); event-driven architecture (message queues and streaming platforms like Kafka/Kinesis/Event Hubs/NATS, event sourcing, dead-letter queues, exactly-once delivery); authentication and authorization (OAuth 2.0, OIDC, JWT, mTLS, RBAC/ABAC, zero-trust); security patterns (input validation, rate limiting, CORS/CSRF, SQL-injection prevention, secrets management, DDoS protection); resilience and fault tolerance (circuit breakers via Hystrix/resilience4j, retry with backoff and jitter, bulkhead isolation, health checks, chaos engineering, idempotency); observability (structured logging with correlation IDs, RED metrics, distributed tracing via OpenTelemetry/Jaeger/Zipkin, APM tools, SLIs/SLOs); data integration patterns (repository/DAO patterns, database-per-service, CQRS, change data capture, connection pooling); caching strategies (cache-aside/read-through/write-through, distributed caching, HTTP caching with ETags, GraphQL persisted queries); asynchronous processing (job queues, scheduled tasks, batch/stream processing, job prioritization); and framework expertise spanning Node.js, Python, Java, Go, C#/.NET, Ruby, and Rust ecosystems. It explicitly defers database schema design to a database-architect skill, infrastructure/cloud specifics to a cloud-architect skill, deep security audits to a security-auditor skill, and system-wide performance optimization to a performance-engineer skill - working after the data layer is designed and complementing those other three roles. Its documented output for an architecture request includes service boundary definitions, API contracts with example requests/responses, a Mermaid service-communication diagram, an auth/authz strategy, resilience and observability strategies, a caching architecture, technology recommendations with rationale, a deployment/rollout plan, a testing strategy, and documented trade-offs.

Use this skill when designing new backend services or APIs, defining service boundaries and data contracts, or planning resilience, scaling, and observability for a backend system. Do not use it for a code-level bug fix, small scripts with no architectural concerns, or frontend/UX guidance - those fall outside its explicit scope, and it defers database schema design, infrastructure specifics, deep security audits, and system-wide performance tuning to their own dedicated skills.

Input is a backend system's domain context, use cases, and non-functional requirements (scale, consistency, latency). Output is service boundary definitions, API contracts (REST/GraphQL/gRPC) with example payloads, a Mermaid architecture diagram, auth/resilience/observability/caching strategies, technology recommendations, a deployment plan, a testing strategy, and documented architectural trade-offs (ADRs), plus a response-compression recommendation (gzip or Brotli) where payload size matters, an APM tool recommendation (e.g. Dynatrace) where deep production tracing is needed, and deployment guidance favoring blue-green and canary release strategies with feature flags for zero-downtime, gradual rollout.

Spans API technologies (REST, GraphQL, gRPC, WebSocket, SSE), messaging/streaming platforms (RabbitMQ, Kafka, AWS SQS/Kinesis, Azure Service Bus/Event Hubs, Google Pub/Sub, NATS), observability tooling (OpenTelemetry, Jaeger, Zipkin, DataDog, New Relic, Grafana), and backend frameworks across Node.js, Python, Java, Go, C#/.NET, Ruby, and Rust; composes with companion database-architect, cloud-architect, security-auditor, and performance-engineer skills.

Engineers and architects designing new backend services, APIs, or microservices architectures who need service boundaries, API contracts, resilience patterns, and observability designed in from the start rather than bolted on later.