DNS Local endpoint preference is not working for TCP DNS requests for Openshift SDN.
Reference code: https://github.com/openshift/sdn/blob/b58a257b896d774e0a092612be250fb9414af5ca/vendor/k8s.io/kubernetes/pkg/proxy/iptables/proxier.go#L999-L1012
This is where the DNS request is short-circuited to the local DNS endpoint if it exists. This is important because DNS local preference protects against another outstanding bug, in which daemonset pods go stale for a few second upon node shutdown (see https://issues.redhat.com/browse/OCPNODE-549 for fix for graceful node shutdown). This appears to be contributing to DNS issues in our internal CI clusters. https://lookerstudio.google.com/reporting/3a9d4e62-620a-47b9-a724-a5ebefc06658/page/MQwFD?s=kPTlddLa2AQ shows large amounts of "dns_tcp_lookup" failures, which I attribute to this bug.
UDP DNS local preference is working fine in Openshift SDN. Both UDP and TCP local preference work fine in OVN. It's just TCP DNS Local preference that is not working Openshift SDN.