Bug report

I did open an issue with fail2ban, but apparently the issue is in python itself.
fail2ban/fail2ban#3438

fail2ban-python -c 'from fail2ban.server.ipdns import DNSUtils; print(DNSUtils.dnsToIp("fail2ban_01"))'

fail2ban_01 is the container name and its hostname

I am sorry , i am not a python dev, so at this moment, the best i can provide as a minimal test is the backtrace.
It will show exactly which function was called, with which paramater, from which file thr function was taken from.

Your environment

• CPython versions tested on: python3.9-3.9.16-1.el9.x86_64
• Operating system and architecture: x86_64 vm on a dell server
• Container inside that vm, run with docker 20.10.22

OS of the vm centos stream 9
OS of the container centos stream 9

ipv6 disabled with net.ipv6.conf.all.disable_ipv6 = 1

Linked PRs

• gh-100795: avoid unexpectedfreeaddrinfo after failedgetaddrinfo #101010
• gh-100795: avoid unexpectedfreeaddrinfo after failedgetaddrinfo #101220
• [3.11] gh-100795: avoid unexpectedfreeaddrinfo after failedgetaddrinfo (GH-101220) #101236
• [3.10] gh-100795: avoid unexpectedfreeaddrinfo after failedgetaddrinfo (GH-101220) #101237
• Revert "gh-100795: avoid unexpectedfreeaddrinfo after failed `geta… #101238
• gh-100795: Don't call freeaddrinfo on failure. #101252
• [3.10] gh-100795: Don't call freeaddrinfo on failure. (GH-101252) #101271
• [3.11] gh-100795: Don't call freeaddrinfo on failure. (GH-101252) #101272