On Wed, Oct 13, 2021 at 4:22 PM Usha Nayak <ushanay@xxxxxxxxx> wrote: > > Need help in understanding the highlighted parameters: > > ProxyPass "/example" "http://backend.example.com"; timeout=3600 keepalive=On > > keepalive parameter - As I understand relates to TCP or socket keep alive probes that are sent to prevent idle connection. > > My confusion is : > > Assuming the backend server takes 4 hrs to process a request and I have 'keepalive on' in Apache httpd with the OS setting to send tcp probes every 2 minutes. Backend server and Apache httpd are sending TCP keep alive packets to indicate the socket connection is not idle. > > In this case, would the 'apache httpd' close the connection in 1 hr ( timeout = 3600) because the 'apache httpd' didn't get the http data? Yes, the timeout= parameter sets the inactivity timeout for the backend connection. If reading from or writing to this connection takes more time than the timeout= va lue then the connection is forcibly closed and an error (504) is returned to the client. The keepalive= parameter is to enable the TCP keepalive mechanism on the connection at the operating system level (SO_KEEPALIVE socket option). As you noted it consists of periodic TCP probes sent by the OS on the connection to prevent intermediaries/routers/firewalls from closing it due to their own TCP inactivity timeout, and also to detect whether the peer is still connected (by acking the probes). The settings for the probes period, ack timeout and number of retries happen at the OS level for all the connections, that's why keepalive= is a simple on/off. Note that the ProxyPass keepalive= parameter must not be confused with the "KeepAlive on/off" directive pertaining to the client connection. The KeepAlive and KeepAliveTimeout directives are about the lifetime of the client connection in between HTTP transactions. Once a request has been handled and a response was sent to the client the KeepAliveTimeout is the time to wait for the next request on the same connection (if "KeepAlive off" the connection is closed immediately and thus each connection handles a single request/response only). FWIW, here is the correspondence between the client side and backend side settings regarding timeout and keepalive: Client side: Proxy/Backend side: Timeout N <=> timeout=N KeepAlive On/Off <=> enablereuse=On/Off KeepAliveTimeout N <=> ttl=N [*Always On*] <=> keepalive=On/Off Hope that helps.. Regards; Yann. --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx
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