Hey Jorge,
I looked into it, and can reproduce the second LISTEN port in a
vanilla Kafka Connect cluster without any connectors running.
Using jstack, I see that there are two threads that appear to be
waiting in the corresponding accept methods:
"RMI TCP Accept-0" #15 daemon prio=5 os_prio=31 cpu=0.37ms
elapsed=790.61s tid=0x0001370f5a00 nid=0x6d03 runnable
[0x00017255e000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.Net.accept(java.base@17.0.4.1/Native Method)
"qtp1530870688-33-acceptor-0@45f75f75-http_8083@43826ec{HTTP/1.1,
(http/1.1)}{0.0.0.0:8083}" #33 prio=3 os_prio=31 cpu=0.17ms
elapsed=789.45s tid=0x00012712e400 nid=0x8707 runnable
[0x0001737ca000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.Net.accept(java.base@17.0.4.1/Native Method)
The latter appears to be the 8083 port which is serving the REST API,
and is expected.
The former appears to be a Java Remote Method Invocation socket on
"port 0" which ends up selecting a random open port on each startup.
I do see that RMI is often used to export JMX metrics, and it appears
that kafka-run-class.sh (which is used when starting Kafka Connect) by
default enables JMX metrics.
I was able to disable the RMI port by setting the
KAFKA_JMX_OPTS="-Dkey=value" environment variable before running
bin/connect-distributed.sh. This isn't a recommendation for you, but
proves that the default KAFKA_JMX_OPTS settings from the
kafka-run-class.sh are relevant.
Thanks for the question, I learned something new!
Greg Harris
On Fri, May 19, 2023 at 4:45 AM Jorge Martin Cristobal
wrote:
>
> Hi all,
>
> I'm testing apache kafka connect for a project and I found that the main
> process listens to two different ports, the one to provide REST api, 8083
> by default, and a different unprivileged port that changes its number each
> restart. For instance, this is fragment of the output from netstat command:
> tcp 0 0 0.0.0.0:8083 0.0.0.0:* LISTEN 28646/java
> tcp 0 0 0.0.0.0:42859 0.0.0.0:* LISTEN 28646/java <--THIS
>
> What's the purpose of that port?. Is there any public definition of that
> interface? I haven't found any documentation wrt that port number.
> Kindly regards,
>
> Jorge M.
