Problem Statement
When should you use Edge Runtime vs Node.js Runtime for API routes and what are the tradeoffs?
Explanation
Use Edge Runtime for lightweight operations that benefit from global distribution like authentication checks, redirects, header manipulation, simple API proxying, or geo-based routing where low latency matters more than capabilities. Edge has millisecond cold starts, runs close to users worldwide for consistent performance, and is cost-effective for high-traffic simple operations, but limits you to around 1-4MB bundle sizes, restricts Node.js APIs like fs or native modules, and may have limited execution time around 30 seconds. Use Node.js Runtime for complex operations requiring full Node.js APIs, large dependencies, database connections, file system access, CPU-intensive tasks, or when using libraries incompatible with Edge constraints. Node.js has higher cold start times, runs in specific regions, costs more at scale, but provides full API access and no bundle size restrictions. Consider hybrid approaches where Edge handles initial routing or auth checks then proxies to Node.js functions for heavy lifting, or use Edge for read-heavy operations and Node.js for writes requiring database transactions.