package: cloud.debian.org (I previously reported this bug again cloud-init, see https://bugs.launchpad.net/cloud-init/+bug/1863773, but it seems it is instead an issue with the Debian images themselves).
I'm using cloud-init on a Debian machien in AWS using the official Debian buster images (https://wiki.debian.org/Cloud/AmazonEC2Image/Buster <https://wiki.debian.org/Cloud/AmazonEC2Image/Buster>) On these machines, ipv6 is disabled by setting /proc/sys/net/ipv6/conf/all/disable_ipv6 to 1. This causes the network to fail: bas@machine:/etc/network$ sudo ifup ens5 Internet Systems Consortium DHCP Client 4.4.1 Copyright 2004-2018 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ <https://www.isc.org/software/dhcp/> Listening on LPF/ens5/02:45:ca:0d:93:76 Sending on LPF/ens5/02:45:ca:0d:93:76 Sending on Socket/fallback DHCPREQUEST for 10.0.16.20 on ens5 to 255.255.255.255 port 67 DHCPACK of 10.0.16.20 from 10.0.16.1 RTNETLINK answers: File exists bound to 10.0.16.20 -- renewal in 1796 seconds. Could not get a link-local address run-parts: /etc/network/if-pre-up.d/cloud_inet6 exited with return code 1 ifup: failed to bring up ens5 Even worse, on boot the machines do get a proper ipv4 address, but (apparently because setting up the network fails), the dhcp (v4) daemon is stopped, and the machines "mysteriously" drop off the net after the lease ends.