RE: [EXTERNAL] Re: [users@httpd] timeout and keepalive parameter in ProxyPass (Apache Users)

I use a different approach to these types of requests.

The back end request immediately returns a status message ”Request Received”

On Subsequent Requests returns a status message ”Working”

Finally, Subsequent Request returns a status message ”Ready” with results.

John Orendt

John.p.orendt@xxxxxxxxxxxxx

From: Usha Nayak <ushanay@xxxxxxxxx>
Sent: Tuesday, October 19, 2021 10:37 AM
To: users@xxxxxxxxxxxxxxxx
Subject: [EXTERNAL] Re: [users@httpd] timeout and keepalive parameter in ProxyPass

Hello

Thank you for your response. However, I'm still a bit fuzzy when it comes to the keepalive and timeout attribute.

I understand keepalive=On attribute by itself but in combination with timeout is where I'm unclear.

In the scenario that I presented with following:

timeout=3600 keepalive=On attributes
backend server taking a long time processing the request sent by client ( note: no streaming any data from server yet since it's busy processing the request, let's say processing time on server is 4 hrs )
OS settings are set to send TCP Keep alive packet in every 2 mins

My guess:

With TCP keep alive probes sent and ACK between 'Apache httpd' machine and 'Backend server' machine, we can be assured that there's no inactive or idle TCP connection.
But, from the 'Apache Httpd' application point of view, it hasn't received the data from the server in 1 hr(3600), and therefore 'Apache Httpd' will initiate a timeout. When the 'Backend Server' is ready in 4 hrs to stream the response back, there's no ' Apache Httpd' client to receive the response.

Please do correct me if I'm thinking this incorrectly,

Appreciate all the help

Thanks.

On Wed, Oct 13, 2021 at 10:03 AM Dino Ciuffetti <dino@xxxxxxxxx> wrote:

The global "Timeout" parameter is needed to set the length of time Apache httpd will wait for I/O in various circumstances.
https://httpd.apache.org/docs/2.4/mod/core.html#timeout

The "keepalive" attribute of ProxyPass can be used to fool your network equipments (like intermediate firewalls) to mantain the tcp connection between apache and its backends open even when no data is passing from and to the wires. Some network equipment like firewalls tend to drop inactive (silent) connections too early (from my experience ~30 min but your mileage may vary).

The "timeout" attribute of ProxyPass is the number of seconds Apache httpd waits for data sent by / to the backend. So in your case apache will close a inactive connection with the backend in 1hr, but while your backend continue to stream data the connection will be kept open. Yes, it's a sort of application timeout.

There is also the "connectiontimeout" attribute of ProxyPass that will consider a new TCP connection with the backend not valid if it takes the specified time to complete (TCP SYN + SYN/ACK + ACK) so it can be retried earlier.

13 ottobre 2021 16:22, "Usha Nayak" <ushanay@xxxxxxxxx> wrote:

Hello

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? Is this timeout 'apache httpd' application timeout ?

Appreciate help.

Thanks.