The duration for which an HTTP connection stays open while waiting for a server to reply is determined by several factors, including the client's behavior, server settings, and intermediate proxies.

  1. Client Behavior: In general, modern web browsers and HTTP clients have timeout settings that control how long they will wait for a response from the server before considering the request failed. The default timeout value for most browsers is around 30-60 seconds, but it can be configured or adjusted in the client-side code.

  2. Server Settings: On the server side, there are several settings that can affect how long a connection stays open. For example, the server may have its own request timeout settings, which determine how long it will wait for a request to be processed before closing the connection. Additionally, server-specific configuration settings or load balancer configurations can also play a role in connection timeouts.

  3. Intermediate Proxies: If there are any intermediate proxies or load balancers between the client and the server, they may have their own timeout settings that can affect the overall duration of the connection.

  4. Keep-Alive: The HTTP Keep-Alive header allows a persistent connection to be maintained between the client and server, enabling multiple requests and responses to be sent over the same TCP connection. If Keep-Alive is enabled and configured, the connection may stay open for subsequent requests without being closed and reopened after each request.

Overall, the exact duration for which an HTTP connection stays open while waiting for a server to reply can vary based on the above factors and their configurations. It's important to consider and set appropriate timeout values at both the client and server sides to ensure proper handling of long-running requests or cases where the server response may take an extended period.

Keep in mind that long-running requests may have implications on server resources, so it's essential to design and optimize your server-side code to handle such scenarios effectively. For very long-running processes, consider using asynchronous processing, background jobs, or pushing the request to a message queue to prevent blocking the HTTP connection for an extended period.

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