Core Software Patterns Everyone Should Know
This isn’t just about what I’ve been building lately—it’s about the software habits and architectural patterns that prepare us for long-term success. Anyone working with me should understand these at a high level, because they’re the building blocks we reuse the most and the glue that holds our systems together.
1) Interfaces Over Implementations
- Define contracts first. APIs, service methods, or ports describe what the system does—not how.
- Swapability. When vendors, frameworks, or tools change, we replace the adapter, not the whole system.
- Pattern: Ports & Adapters (Hexagonal Architecture).
Takeaway: Think in terms of capabilities (payments, storage, email) rather than vendor-specific code.
2) Context & Factories
- Context objects carry identity, tenant, roles, and environment.
- Factories use that context to create the right DB client, service, or adapter.
- Ensures everything is scoped and isolated, especially in multi-tenant systems.
Takeaway: Build once, use everywhere—factories prevent mistakes and maximize reuse.
3) Repositories & Services
- Repositories: Safe, tenant-aware data access (queries wrapped, no raw SQL leaks).
- Services: Business rules, validation, pricing, workflows.
- Keeps separation of concerns: data logic vs. domain logic.
Takeaway: Clear layers reduce duplication and make testing easier.
4) Idempotency & Reliability
- Idempotency keys: Prevent double charges or duplicate records.
- Retry with backoff: Handle transient errors gracefully.
- Outbox/In-box pattern: Ensure reliable delivery in event-driven flows.
- Saga pattern: Manage multi-step processes with compensation.
Takeaway: Systems should survive retries, crashes, and network hiccups without breaking.
5) Tenant Isolation & Multi-Tenancy
- Tenant context always in scope.
- Shared DB (row-level security) for efficiency.
- Dedicated schema/DB for large or regulated customers.
- Feature flags per tenant for safe rollout.
Takeaway: One app, many customers—each in their own safe bubble.
6) Security by Habit
- Principle of least privilege: Give systems and users only what they need.
- Secrets management: Keys in vaults, never in code or logs.
- Audit trails: Who did what, when, and where.
- Progressive hardening: Start safe, add MFA, BYOK, egress controls as risk grows.
Takeaway: Security isn’t a feature—it’s the default posture.
7) Observability & Feedback Loops
- Structured logs (with tenantId, userId, requestId).
- Metrics: latency, error rate, throughput, saturation.
- Tracing: follow requests across services.
- Dashboards & alerts: measure user impact, not noise.
Takeaway: You can’t fix what you can’t see. Instrument everything.
8) Data & API Patterns
- Schema validation: validate at edges (inputs/outputs).
- DTOs & mappers: decouple internal models from external contracts.
- Pagination: consistent (cursor preferred).
- Soft deletes + versioning: safer than destructive deletes.
Takeaway: Treat data as a contract—stable, explicit, and versioned.
9) Front-End & UX Patterns
- Headless components: logic in hooks/controllers; UI in small components.
- State boundaries: remote (server cache) vs. local (UI-only).
- URL as state: filters, search, pagination.
- Design tokens: shared spacing, colors, typography for consistency.
Takeaway: Frontend code should be modular, testable, and reusable across projects.
10) Workflow & Content Patterns
- Schema-driven forms: define once, render anywhere.
- Content-relations model: articles, events, companies linked predictably.
- Seed scripts: idempotent data population for dev/stage/prod.
- Issue templates: consistency in planning and acceptance criteria.
Takeaway: Build tools that reduce manual work and enforce consistency.
11) Testing & Quality
- Unit tests: validate small functions.
- Contract tests: guarantee external APIs behave as expected.
- Integration tests: check flows across services.
- Fixtures: realistic data seeds for repeatable runs.
Takeaway: Testing is less about coverage, more about confidence.
12) Documentation & Naming
- One doc per capability: what it does, inputs/outputs, failure modes.
- Consistent naming: ports = nouns (
Payments
), methods = verbs (charge
,refund
). - Diagrams: flows (booking, checkout, refund, etc.) should be visualized.
Takeaway: Shared language makes scaling teams possible.
13) What We Reuse the Most
- Tenant context + factories
- Schema-driven forms & pricing engines
- Webhook gateway (verified, idempotent, tenant-routed)
- Upload pipeline (typed, scanned, signed URLs)
- Content + relationships (articles/events/companies)
- Audit & telemetry (same patterns everywhere)
These aren’t one-off hacks—they’re patterns we keep returning to, because they solve the same problems across projects.
Final Thought
Reusable patterns = shared wisdom.
The more we align on these principles, the less time we waste reinventing solutions.
The goal isn’t just to build software—it’s to build a culture of software that’s reliable, adaptable, and understandable to anyone joining the team.