Backend Engineer

REST API Design

Why: You make design calls such as idempotent retries on payments or PUT versus PATCH, so integrators can retry safely after a timeout without creating duplicates.

API Versioning & Documentation

Why: You can tell a breaking change from a safe one and publish an OpenAPI spec, so shipping a field rename does not silently break a partner's integration.

Relational Database Design

Why: You decide when to normalize and when to denormalize, and which indexes a new feature needs, so the table stays workable once it grows past a million rows.

SQL Query Optimization

Why: You read an execution plan to find why a report query takes seconds and fix it with the right index or rewrite, instead of adding hardware or caching around it.

Authentication Patterns (JWT/OAuth2/OIDC)

Why: You implement token refresh and choose between OAuth2 flows for a new client, so users stay signed in securely and a leaked access token has a short life.

Authorization Models (RBAC/ABAC)

Why: You model roles and permissions for a feature, including per-tenant checks, so a user from one customer cannot read another customer's records by changing an id.

Layered Architecture

Why: You keep business rules out of controllers and behind interfaces, so you can swap a database or test a pricing rule without booting the whole web stack.

Error Handling & Logging

Why: You design an exception hierarchy and log levels that map failures to the right response, so on-call can separate a client mistake from a real outage in aggregated logs.

Health Checks & Monitoring

Why: You separate liveness from readiness and expose metrics for your service, so the orchestrator stops routing traffic to an instance whose database connection is gone.

Message Queues & Async Processing

Why: You move slow work such as emails or report generation onto a queue with idempotent consumers and a dead letter queue, so a retry never charges or sends twice.

Caching Strategies

Why: You apply cache-aside with a sensible TTL to a hot read path and know what invalidates it, so response times drop without users seeing stale prices.