Backend Development Agency — APIs & Infrastructure

Backend development covers everything that runs on the server — the APIs your frontend calls, the database storing your data, the authentication system verifying users, background jobs processing work asynchronously, and the cloud infrastructure everything runs on. It is invisible to users but essential to every product.

Our primary backend stack is Node.js with TypeScript — specifically Fastify or Express for APIs. For data-heavy or AI workloads we use Python with FastAPI. For performance-critical microservices we use Go. We choose the right tool for each project rather than defaulting to a single stack.

We follow RESTful conventions — resource-based URLs, correct HTTP verbs and status codes, consistent error response shapes, and versioning via URL prefix (v1/). We document every endpoint with OpenAPI/Swagger, generating interactive docs that frontend teams can use without asking questions.

PostgreSQL is our default for relational data — it is reliable, feature-rich, and handles both structured and semi-structured (JSONB) data well. MongoDB for document-centric use cases with truly schema-less data. Redis for caching, sessions, and pub/sub. We avoid NoSQL for data that is inherently relational.

We implement JWT-based auth with short-lived access tokens (15–60 min) and rotating refresh tokens stored in httpOnly cookies. Social login via OAuth 2.0 (Google, GitHub). Authorization uses RBAC — roles attached to users, checked in middleware before handler execution.

We profile slow endpoints with query analysis tools (EXPLAIN ANALYZE), add targeted database indexes, implement Redis caching for hot read paths, paginate large result sets, use connection pooling (PgBouncer), and set response compression for large payloads.

We use BullMQ with Redis for durable, retryable background jobs — sending emails, processing webhooks, generating reports, resizing images. Jobs have configurable retry counts with exponential backoff, a dead-letter queue for failed jobs, and a Bull Board dashboard for visibility.

We apply defense in depth: HTTPS everywhere, security headers (helmet.js), rate limiting per user and IP, input validation at the API boundary (Zod), parameterized queries to prevent SQL injection, JWT with proper expiry, secrets in environment variables, and regular dependency audits.

Files go directly from the client to S3 or Cloudinary via pre-signed upload URLs — the backend is never in the file transfer path. This offloads bandwidth from your API server, enables multipart uploads for large files, and lets you apply CDN delivery and image transformations immediately.

We test at three levels: unit tests for pure business logic, integration tests for database and external service interactions (using Docker test containers), and contract tests to verify API response shapes. We target 80%+ coverage on business logic and run all tests in CI on every pull request.

We configure structured JSON logging with request IDs for tracing, expose /health and /metrics endpoints, integrate Sentry for exception tracking, set up uptime monitoring with PagerDuty or BetterUptime alerts, and add APM for slow endpoint detection on high-traffic APIs.

A standalone API backend takes 4–8 weeks. A complete backend with auth, jobs, file storage, and third-party integrations takes 2–4 months. Kultrix delivers backend projects with API documentation, deployment runbooks, and test coverage reports as standard deliverables.