Re: Getting intermittent mod_jk errors on 1 / 3 web servers

On 30/10/2025 14:06, Christopher Schultz wrote:

<snip/>

> That symptom, plus the "this is the only server using a NAT gateway" 
> would surely point to one place: the NAT gateway is killing connections 
> that are idle and surprising both stunnel and mod_jk. I can also see a 
> graph of non-zero numbers of "Idle Timeouts" on the NAT gateway. It 
> doesn't tell me more details about those timeouts, but they are almost 
> certainly outgoing AJP/stunnel connections.

Your reasoning above looks sound to me.

> But.
> 
> Here is my mod_jk workers configuration:
> 
> # Template worker
> worker.template.type=ajp13
> worker.template.host=localhost
> worker.template.connection_pool_timeout=60
> worker.template.socket_timeout=300
> worker.template.max_packet_size=65536
> 
> worker.node1.reference=worker.template
> worker.node1.port=7015
> worker.node1.route=node1
> 
> My expectation is that connection_pool_timeout of 60 (seconds) will 
> close connections which have been idle for 60 seconds. If mod_jk closes 
> a connection, stunnel will also close that connection. (Note: I have no 
> explicit connectionTimeout or keepAliveTimeout on the Tomcat side. But 
> this doesn't seem to be any problem for the other two web servers.)
> 
> Checking my configuration for the NAT gateway, it has a fixed idle 
> timeout of 350 seconds, which is much longer than the 60 seconds I 
> (believe I) have set for idle AJP connections.
> 
> I do not use servlet async or Websocket for anything in my application, 
> so I do not expect long-lasting connections between client and server.
> 
> Is there anything I haven't checked at this point?

You might want to check how connection_pool_timeout interacts with 
connection_pool_size and connection_pool_minsize.

I am wondering if the current size is at minsize will an idle connection 
be closed if it exceeds the timeout?

I think the code that handles this is here:

https://github.com/apache/tomcat-connectors/blob/main/native/common/jk_ajp_common.c#L3510

and I think it only closes idle connections until the pool reaches minsize.

Which isn't what the docs suggest. Which in turn might explain why you 
are seeing connections open longer than the NAT gateway timeout.

Rainer understands this code far better than I do. It would be good to 
get his view on this. If I am right, I think we either need to update 
the docs or we need to fix the code so idle connections below minsize 
are closed and then re-opened to refresh them.

Mark