proxy_send_timeout time;
Default: proxy_send_timeout 60s;
Context: http, server, location
Set the timeout period for "Transmit a request to the proxy server". This timeout period is between two write operations, not the timeout period of the entire request. If within this time, the proxy server does not receive anything, it closes the connection.
proxy_read_timeout time;
Default: proxy_read_timeout 60s;
Context: http, server, location
Set the timeout period for "read response from a proxy server". This timeout period is between two read operations, not the timeout period of the entire response. If the proxy server does not transmit anything during this time, the connection is closed.
About the HTTP proxy module
references
WikiNotes / ngx http proxy module
Nginx / Module ngx_http_proxy_module