To optimize a Node.js application for high concurrency, the key is to make sure the event loop isn’t blocked by long-running or synchronous operations. Since Node.js is single-threaded, blocking the event loop will prevent other requests from being handled. Using non-blocking I/O operations, like asynchronous file reads and database queries, is crucial for maintaining concurrency. You can also implement clustering, which allows your app to run on multiple CPU cores simultaneously, thereby increasing the number of concurrent requests that can be handled. Load balancing can help distribute incoming requests across multiple instances or even different servers to manage high traffic more effectively. Tools like NGINX or HAProxy can be used for this purpose. Additionally, reducing the complexity and size of your responses, caching common data, and using efficient database indexing can further optimize the app for concurrency. By focusing on asynchronous patterns and distributing load efficiently, you can build a Node.js app that scales gracefully even under heavy traffic.