Kea leaks file descriptors when performing a reload

name: Kea leaks file descriptors when performing a reload
about: This can be problematic for some scripts

Describe the bug

If you perform a reload by systemd or calling an API call, it will leak. We noticed this issue when we had a really bad script to perform reload pretty often. This obviously hit a default limit of open file descriptors per process (1024), which resulted in constant log spam and crash.

To Reproduce

Steps to reproduce the behavior:

1. Get the current amount of file descriptors for Kea DHCPv4/v6/CA PID. You can use a script provided below.

for i in $(ps -C "${SEARCH}" -o pid | grep -v PID)
do
     echo "$(ls -l /proc/${i}/fd | wc -l)"
done

and then run: SEARCH=kea-dhcp4 ./script.sh

this will give me a value 49 for example

2. Perform a reload by an API call or systemctl reload isc-kea-dhcp4-server
3. Run the script again: SEARCH=kea-dhcp4 ./script.sh
4. Value changes from 49 to 52

This also happens for other Kea services like Control Agent.

Expected behavior

It shouldn't leak, the number of file descriptors should be lower or stay the same.

Environment:

• Kea version: 2.6.0 (can be reproduced on older versions)
• OS: Debian 12
• Kea hooks: HA, MySQL, stat_cmds, lease_cmds, perfmon