7 Production Issues Every Spring Boot Developer Should Learn Before Becoming Senior

After working on enterprise applications and distributed microservices, I have realized that the biggest challenges rarely come from writing business logic. They come from handling production traffic, failures, concurrency, and unexpected edge cases. Here are seven lessons that every Spring Boot developer should know before calling themselves a senior engineer. 1. Never Assume an API Will Be Called Only Once One of the most common mistakes is assuming a client sends exactly one request. In reality: Users refresh the page. Mobile apps retry automatically. API gateways retry requests. Kafka consumers may reprocess events. Network failures cause duplicate submissions. If your endpoint creates an order, payment, or booking every time it receives a request, duplicates are almost guaranteed. Better Approach Design APIs to be idempotent . For example: Use an Idempotency-Key. Store processed request IDs. Ignore duplicate requests safely. Production systems should always expect duplicate requests. 2. Database Transactions Are Not Enough Many developers believe this solves everything: @Transactional public void createOrder () { ... } It doesn't. A transaction protects changes inside a single database . It does not protect: Kafka publishing Email sending External REST APIs Redis updates File uploads If your database commits successfully but Kafka publishing fails, your system is already inconsistent. Better Approach Use patterns such as: Transactional Outbox Saga Pattern Event-driven architecture Retry with dead-letter queues 3. Don't Trust External APIs Every external service will eventually fail. Your payment provider. Your authentication service. Your notification service. Even your own internal microservices. Never assume another service is always available. Add Protection Timeouts Retries Circuit Breakers Fallback logic Monitoring Failing fast is usually better than waiting forever. 4. Logging Is More Valuable Than You Think When production goes down, nobody asks: "Was th