Comment 8 for bug 1791578

@glenn-w, are you seeing this with a DHCP server sending multiple domains in DHCP option 15 (which is not RFC2132 compliant) or are you reporting a new bug where systemd-resolved is broken when the DHCP server provides multiple hosts via DHCP option 119? If this is an issue with DHCP option 119 then a new bug should be filed[0] against systemd with steps to recreate instead of reusing this bug which is specific to AWS EKS images and DHCP option 15 non-compliant server behavior.

While this issue is not specific to AWS, AWS's DNS server does exhibit this behavior as acknowledged in their documentation[1]. The underlying cause of the issue in this bug report is a DHCP server not complying with the RFC2132 and sending multiple domains in option 15 rather than using DHCP option 119 for multiple domains. An excellent write-up is available on Igo Cicimov's blog[2].

[0] https://bugs.launchpad.net/ubuntu/+source/systemd/+filebug
[1] https://docs.aws.amazon.com/vpc/latest/userguide/VPC_DHCP_Options.html#DHCPOptionSets
[2] https://icicimov.github.io/blog/devops/aws-ubuntu-systemd-resolved-dns-issues/