TCP Keepalive v HTTP Keepalive?

HTTP Keep-alive timeout is mostly controlled by the server. Example, Server says, if you don't send me a request, after 15 seconds of idleness, I will close the connection.

When server closes the connection, the TCP idle timeout is irrelevant, because connection is explicitly being closed.

So in effect, http keep-alive timeout overrides the TCP one. If conneciton is closed for any reason, then client must initiate a new connection to send a new request.

The TCP idle timeout is only in effect if the connection is idle (no data transmitted) and the connection was not closed for any other reason (such as http keep-alive timeout). You can think of it as the default timeout when nothing else closes the connection.