Validated Fastify Configuration with dotenv, env-schema, and @fastify/env

This article provides a comprehensive tutorial on implementing validated configuration in Fastify applications using @fastify/env, dotenv, and env-schema. It explains how to load environment variables from .env files, validate them against a JSON Schema using AJV, and attach the validated config to the Fastify instance. The guide covers background, step-by-step implementation, trade-offs, alternatives like convict and envalid, and best practices for security, troubleshooting, and performance. Aimed at developers building Node.js services with Fastify who want to avoid runtime errors from missing or mistyped environment variables.