If your Node.js + Express application is dropping requests, it can be caused by various factors. Here are some common reasons and solutions to address dropped requests:

  1. Insufficient Resources: Check if your server has enough resources (CPU, memory, etc.) to handle incoming requests. Dropping requests can occur when the server is overloaded and cannot handle all incoming traffic. Consider upgrading your server or optimizing your application's performance.

  2. Concurrency Limit: Node.js has a default concurrency limit that restricts the number of simultaneous connections it can handle. You can increase this limit using the --max-http-header-size flag when starting your Node.js server:

    node --max-http-header-size=<size> app.js

    Replace <size> with a higher value (e.g., 8192) if you suspect that large request headers are causing the dropped requests.

  3. Blocking Operations: Make sure that your application is non-blocking and doesn't perform long-running or synchronous operations that can delay the event loop. Use asynchronous functions and offload heavy tasks to worker threads or background processes.

  4. Error Handling: Check your application's error-handling mechanisms. If an unhandled error occurs during the request processing, it can lead to dropped requests. Always handle errors properly to avoid application crashes.

  5. Firewalls and Load Balancers: If your application is behind a firewall or load balancer, check their settings to ensure they are not dropping requests based on certain criteria, such as rate limiting or security rules.

  6. Reverse Proxy Misconfiguration: If you are using a reverse proxy (e.g., Nginx, Apache) to forward requests to your Node.js server, verify that the proxy configuration is correct and not causing any request drops.

  7. Networking Issues: Dropped requests can be caused by network-related problems. Check your server's network configuration, DNS settings, and firewall rules.

  8. Logging and Monitoring: Implement logging and monitoring in your application to track dropped requests and diagnose potential issues. Log any errors, failed requests, or unusual behavior to identify the root cause.

  9. Rate Limiting: Consider implementing rate limiting to prevent abuse and excessive requests from overwhelming your server.

By investigating these possible causes and implementing the appropriate solutions, you can address dropped requests and ensure that your Node.js + Express application handles incoming traffic reliably and efficiently.

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