Chapter 4: System architecture and technical design

Architecture is your product’s backbone. It determines how fast you can ship, how safely you can scale, and how easily you can evolve. This chapter gives novice and experienced builders a clear, decision-ready view of trending architectures, their pros/cons, enterprise-grade tech choices, indicative adoption, and the practical path to reshape your stack from MVP to microservices. You’ll see how to apply this to a developer-first Todo List SaaS with GitHub, Slack, and Jira integrations.

What is system architecture and technical design?

Definition:

System architecture: The high-level structure of your product’s components and how they interact (frontend, backend, data, integrations, infra, security, observability).
Technical design: The detailed choices and patterns that implement the architecture (frameworks, protocols, data models, tenancy strategy, deployment topology).

Why it matters:

Scalability: Handles growth in users, features, and data.
Reliability: Minimizes downtime and regression risk.
Velocity: Enables teams to ship quickly and safely.
Compliance: Supports isolation, auditability, and governance.

Visual: Architecture layers

Clients → Frontend → API gateway → Services → Data stores → Messaging → Observability → CI/CD → Cloud & security controls

Real-life examples

Company	Early architecture	Scale architecture	Why the shift
Slack	Modular monolith + queues	Event-driven microservices (Kafka), sharded data	Real-time messaging at scale, cross-workspace isolation
GitHub	Monolith (Ruby on Rails)	Service-oriented + APIs, Actions platform	Extensibility, marketplace, CI/CD workflows
Shopify	Rails monolith + MySQL	Modular monolith + background jobs, selective services	Strong developer productivity, predictable scaling
Netflix	Service-oriented	Microservices + edge gateways + chaos engineering	Global scale, diverse device ecosystem

These teams moved gradually: stabilize MVP, optimize hotspots, then split along clear domain boundaries. They avoided premature complexity and kept strong developer ergonomics.

Apply to your demo SaaS: Todo List with integrations

Layer	Decision (MVP → Growth)
Frontend	Next.js (MVP) → Next.js App Router + design system (growth)
Backend	Node.js (Fastify/NestJS) modular monolith → split “Integrations”, “Tasks”, “Rituals”, “Auth” services
Data	PostgreSQL (row-level security for multi-tenancy) → read replicas + schema-per-tenant for enterprise isolation
Messaging	Redis (BullMQ) for jobs → Kafka/NATS for event-driven integrations and analytics
Integrations	OAuth + webhooks (GitHub/Slack/Jira) → connector services with retry/DLQ
Infra	Vercel + managed Postgres (MVP) → Docker + Kubernetes (AKS/EKS/GKE) with Argo CD
Security	JWT + RBAC → OIDC + SSO (SAML), audit logs, policy-as-code (OPA)
Observability	Sentry + basic logging → Prometheus/Grafana + OpenTelemetry + Loki/Jaeger