Hexagonal Architecture in TypeScript: Interview Questions to Expect in 2027

This is a practical, up-to-date guide to Hexagonal Architecture — what it is, why it matters in 2026, and how to apply it in real projects. It is written for developers and founders who want clear answers and proven best practices, not filler.

Whether you're just starting out or leveling up, treat this as a working reference you can return to. Every section is built to be skimmed, applied, and shared.

What Are the SOLID Principles?

SOLID is five object-oriented design principles that make code easier to extend and maintain. They guide where responsibilities and dependencies should live.

• Single Responsibility: a class should have one reason to change.
• Open/Closed: open for extension, closed for modification.
• Liskov Substitution: subtypes must be usable wherever their base type is expected.
• Interface Segregation: prefer many small interfaces over one fat one.
• Dependency Inversion: depend on abstractions, not concrete implementations.

Applied with judgment, they reduce coupling and make changes local. Applied dogmatically, they cause over-engineering and needless indirection. Treat them as heuristics that point toward flexible designs, not rigid rules to satisfy in every class.

Why Is Observability Critical in Production?

You cannot fix what you cannot see. Observability is the ability to understand a system's internal state from its outputs, and it turns mysterious outages into diagnosable events.

It rests on three pillars:

• Logs: structured, searchable records of discrete events.
• Metrics: numeric time-series like latency, error rate, and throughput.
• Traces: end-to-end request paths across services.

Track the signals that reflect user experience, often summarized as latency, traffic, errors, and saturation. Alert on symptoms users feel, not on every internal blip, to avoid alert fatigue. In distributed systems especially, distributed tracing is what makes it possible to pinpoint which service in a long call chain caused a slowdown or failure.

What Is the Difference Between a Monolith and Microservices?

A monolith deploys all functionality as a single unit, sharing one codebase, build, and process. Microservices split capabilities into independently deployable services that communicate over the network, each owning its data.

Monoliths are simpler to build, test, and debug early on, with no network calls between modules and easy transactions. Microservices offer independent scaling and deployment but add operational complexity: service discovery, distributed tracing, network failure handling, and eventual consistency.

Key decision factors:

• Team size and whether teams can own services autonomously
• Operational maturity (CI/CD, monitoring, on-call)
• Whether different components genuinely need different scaling

Most teams should start with a well-structured modular monolith and extract services only when a clear boundary and need emerge.

How Do Caching Strategies Improve Performance?

Caching stores the result of expensive work closer to where it is needed, trading memory and freshness for speed. Effective caching can cut database load and shave hundreds of milliseconds off response times.

Common patterns and where they fit:

• Cache-aside: application checks the cache, loads from the source on a miss, then populates it. The most common pattern.
• Write-through: writes go to cache and store together for consistency.
• Write-back: writes hit cache first and flush later for throughput.
• CDN/edge caching: serves static and cacheable responses near users.

The hard part is invalidation. Set sensible TTLs, version cache keys, and decide whether stale data is acceptable for each use case.

How Should You Design a REST API?

A good REST API is predictable, consistent, and self-documenting. Model resources as nouns, use HTTP methods for actions, and let status codes carry meaning rather than embedding errors in 200 responses.

Principles that hold up well:

• Use plural nouns: /users, /users/42/orders.
• Map verbs to methods: GET reads, POST creates, PUT/PATCH update, DELETE removes.
• Return correct status codes: 200, 201, 400, 401, 404, 409, 422, 500.
• Support pagination, filtering, and sorting via query parameters.
• Version the API and keep responses consistent in shape.

Make the API safe to evolve by adding fields without breaking clients and documenting deprecations. Idempotency for writes prevents duplicate effects when clients retry on flaky networks.

How Do You Write Effective Tests?

Tests exist to give you confidence to change code quickly. The most valuable suites are fast, deterministic, and focused on behavior rather than implementation details.

A practical balance follows the testing pyramid:

• Many fast unit tests covering logic and edge cases.
• Fewer integration tests verifying components work together.
• A small number of end-to-end tests for critical user journeys.

Write tests that read like specifications, use clear arrange-act-assert structure, and avoid brittle assertions tied to internal structure. Flaky tests erode trust faster than missing ones, so quarantine and fix them promptly. High coverage is not the goal in itself; meaningful coverage of risky paths and business rules is what actually prevents regressions.

Hexagonal Architecture: Key Facts and Data

According to recent industry research and the official documentation linked below:

• Database connection pooling commonly caps active connections to 10-100 to avoid exhausting server resources
• Redis can sustain over 100,000 operations per second on a single commodity node
• HTTP responses with proper Cache-Control headers can eliminate repeat network requests entirely for their max-age duration

Quick-Reference Summary

A map of what this guide covers:

Topic	What you'll learn
What Are the SOLID Principles?	SOLID is five object-oriented design principles that make code easier to extend and maintain.
Why Is Observability Critical in Production?	You cannot fix what you cannot see.
What Is the Difference Between a Monolith and Microservices?	A monolith deploys all functionality as a single unit, sharing one codebase, build, and process.
How Do Caching Strategies Improve Performance?	Caching stores the result of expensive work closer to where it is needed, trading memory and freshness for speed.
How Should You Design a REST API?	A good REST API is predictable, consistent, and self-documenting.
How Do You Write Effective Tests?	Tests exist to give you confidence to change code quickly.

How to Get Started with Hexagonal Architecture

A simple path that works:

1. Learn the fundamentals of Hexagonal Architecture from primary sources, not just tutorials.
2. Build one small, real project end to end.
3. Get feedback, refactor, and add tests.
4. Ship it publicly and document what you learned.
5. Repeat with a slightly harder project each time.

Build It with a World-Class Full Stack Developer

Sandeep Kumar Chaudhary is a full stack world-class developer. If you want to turn this into a real, production-ready product, get in touch — message directly on WhatsApp at +9779802348957 for a fast, no-pressure consult.

You can also explore the projects already shipped to thousands of users, or start a conversation here.

Final Thoughts

Indexes accelerate reads but add write and storage cost, so apply them deliberately. The developers and teams who win in 2026 pair strong fundamentals with consistent shipping. Start small, stay curious, build in public, and revisit this guide as your skills grow.

Sources and Further Reading

• MDN Web Docs
• web.dev by Google
• PostgreSQL Documentation
• Redis Documentation
• Kubernetes Documentation
• AWS Architecture Documentation