HTTP Keep Alive and TCP keep alive

Http Problem Overview

How is HTTP Keep Alive implemented? Does it internally use TCP Keep Alive? If not, how does the server detect if the client is dead or alive?

Http Solutions

Solution 1 - Http

I know this is an old question, but still:

HTTP Keep-Alive is a feature that allows HTTP client (usually browser) and server (webserver) to send multiple request/response pairs over the same TCP connection. This decreases latency for 2nd, 3rd,... HTTP request, decreases network traffic and similar.
TCP keepalive is a totally different beast. It keeps TCP connection opened by sending small packets. Additionally, when the packet is sent this serves as a check so the sender is notified as soon as connection drops (note that this is NOT the case otherwise - until we try to communicate through TCP connection we have no idea if it is ok or not).

To answer your questions about HTTP Keep-Alive:

How is HTTP Keep Alive implemented?

To put it simply, the HTTP server doesn't close the TCP connection after each response but waits some time if some other HTTP request will come over it too. After some timeout it closes it anyway.

Does it internally use TCP Keep Alive?

No, at least I see no point in it.

If not, how does the server detect if the client is dead or alive?

It doesn't - it doesn't need to. If a client sends a request, it will get the response. If the client doesn't send anything over TCP connection (maybe because the connection is dead) then a timeout will close the connection; client will of course notice this and will send request through another TCP connection if needed.

Solution 2 - Http

HTTP Keep-Alive is a feature of HTTP protocol. The web-server, implementing Keep-Alive Feature, has to check the connection/socket periodically (for incoming HTTP request) for the time span since it sent the last HTTP response (in case there was corresponding HTTP Request). If no HTTP request is received by the time of the configured keep-alive time (seconds) the web server closes the connection. No further HTTP request will be possible after the 'close' done by Web Server. On the other hand, TCP Keep-Alive is managed by OS in the TCP layer. HTTP Keep-Alive and TCP Keep-Alive is totally unrelated things.

Solution 3 - Http

HTTP keep-alive, a.k.a., HTTP persistent connection, is an instruction that allows a single TCP connection to remain open for multiple HTTP requests/responses.

By default, HTTP connections close after each request. When someone visits your site, their browser needs to create new connections to request each of the files that make up your web pages (e.g. images, Javascript, and CSS stylesheets), a process that can lead to high page load times.

Enabling the keep-alive header allows you to serve all web page resources over a single connection. Keep-alive also reduces both CPU and memory usage on your server.

Source: https://www.imperva.com/learn/performance/http-keep-alive/

Solution 4 - Http

http keep-alive is just making tcp living longer in order to transfer multi http request.After keep-alive timeout, the tcp connection will be closed. tcp keep-alive is just a mechanism keeping the tcp connection,or check the tcp connection is not closed

Content Type	Original Author	Original Content on Stackoverflow
Question	Bruce	View Question on Stackoverflow
Solution 1 - Http	johndodo	View Answer on Stackoverflow
Solution 2 - Http	Ayub	View Answer on Stackoverflow
Solution 3 - Http	Mahdi Bashirpour	View Answer on Stackoverflow
Solution 4 - Http	stevencjh	View Answer on Stackoverflow