Poor scaling in a Node.js app often results from blocking operations, limited resources, or inefficient database queries. Load balancing, clustering, and optimizing I/O can help.

If your Node.js app isn't scaling well under heavy load, it’s likely due to a combination of factors such as blocking operations, inefficient resource management, or slow I/O operations. Node.js operates on a single-threaded event loop, so any blocking operation—like a long-running database query or file I/O—can prevent the app from handling more requests concurrently. To scale effectively, it’s essential to eliminate blocking code by refactoring synchronous tasks into asynchronous ones using async/await or callbacks. Another technique is to implement load balancing and clustering, which allows multiple instances of your app to run on different cores of the CPU, distributing the load evenly. Horizontal scaling, where you add more servers to handle traffic, is another option. You should also optimize database queries, caching frequently accessed data, and reducing the size of responses sent to the client. By optimizing resource use and leveraging Node.js’s asynchronous capabilities, you can improve the scalability of your app to handle high traffic efficiently.