Relationship of Proxy_Read_timeout, keep alive and proxy connection

Hi All,

I'm a newbie to the nginx and I have configured a nginx reverse proxy to communicate with apache server. Recently I got an error like
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2018/03/24 00:11:58 [error] 19840#0: *2902980 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 82.132.236.172, server: ~^[A-Za-z0-9,-]*\.orangehrmlive\.com$, request: "POST /auth/validateCredentials HTTP/1.1", upstream: "https://[::1]:9191/auth/validateCredentials", host: "******", referrer: "******"

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After going through several articles I found out that increasing the proxy_read_timeout will resolve the problem. My current nginx timeout configurations :
fastcgi_read_timeout 300;
proxy_connect_timeout 300;
proxy_send_timeout 300;
proxy_read_timeout 300;
keepalive_timeout 65;

My concern is while having keep_alive_timeout as 65 seconds, Why do I need to increase proxy_read_timeout again? Please, can you explain me the relationship between those directives so that I can understand the scenario? Any advice or guidance would be highly appreciated.

Thanks.