When I have a custom search domain, the domain name with the svc.cluster.local suffix cannot be resolved within the k8s cluster - linux

Question

When I add a custom search such as abc to /etc/resolv.conf on the node, the full service.namespace.svc.cluster.local domain name cannot be resolved inside the pod。
This is the content of /etc/resolv.conf inside my pod
nameserver 100.96.0.10
search system.svc.cluster.local svc.cluster.local cluster.local abc
options ndots:5
When I resolve short domain names such as apigateway. It can be resolved normally
bash-5.1# nslookup apigateway
Server: 100.96.0.10
Address: 100.96.0.10#53
Name: apigateway.system.svc.cluster.local
Address: 100.96.101.242
or something like this
bash-5.1# nslookup apigateway.system
Server: 100.96.0.10
Address: 100.96.0.10#53
Name: apigateway.system.svc.cluster.local
Address: 100.96.101.242
bash-5.1# nslookup apigateway.system.svc
Server: 100.96.0.10
Address: 100.96.0.10#53
Name: apigateway.system.svc.cluster.local
Address: 100.96.101.242
But when I add cluster.local it can't resolve
bash-5.1# nslookup apigateway.system.svc.cluster.local
Server: 100.96.0.10
Address: 100.96.0.10#53
*** Can't find apigateway.system.svc.cluster.local.abc: No answer
The external domain name also cannot be resolved
bash-5.1# nslookup www.github.com
Server: 100.96.0.10
Address: 100.96.0.10#53
*** Can't find www.github.com.abc: No answer
From the coredns log, we can see that when the full domain name apigateway.system.svc.cluster.local.abc. is queried, coredns returns noerror. But in fact the domain name does not exist
[INFO] 100.64.2.137:40043 - 60409 "AAAA IN apigateway.system.svc.cluster.local.system.svc.cluster.local. udp 78 false 512" NXDOMAIN qr,aa,rd 171 0.00021492s
[INFO] 100.64.2.137:40043 - 59971 "A IN apigateway.system.svc.cluster.local.system.svc.cluster.local. udp 78 false 512" NXDOMAIN qr,aa,rd 171 0.000247841s
[INFO] 100.64.2.137:56051 - 8509 "A IN apigateway.system.svc.cluster.local.cluster.local. udp 67 false 512" NXDOMAIN qr,aa,rd 160 0.000146127s
[INFO] 100.64.2.137:56051 - 8780 "AAAA IN apigateway.system.svc.cluster.local.cluster.local. udp 67 false 512" NXDOMAIN qr,aa,rd 160 0.000197555s
[INFO] 100.64.2.137:50812 - 47345 "AAAA IN apigateway.system.svc.cluster.local.svc.cluster.local. udp 71 false 512" NXDOMAIN qr,aa,rd 164 0.000198486s
[INFO] 100.64.2.137:50812 - 47072 "A IN apigateway.system.svc.cluster.local.svc.cluster.local. udp 71 false 512" NXDOMAIN qr,aa,rd 164 0.000296226s
[INFO] 100.64.2.137:50985 - 42386 "AAAA IN apigateway.system.svc.cluster.local.abc. udp 57 false 512" NOERROR qr,aa,rd,ra 57 0.026135963s
[INFO] 100.64.2.137:50985 - 41590 "A IN apigateway.system.svc.cluster.local.abc. udp 57 false 512" NOERROR qr,aa,rd,ra 57 0.059998825s
After I removed this custom search domain everything went back to normal
bash-5.1# nslookup www.github.com
Server: 100.96.0.10
Address: 100.96.0.10:53
Non-authoritative answer:
www.github.com canonical name = github.com
Name: github.com
Address: 20.205.243.166
Non-authoritative answer:
www.github.com canonical name = github.com
bash-5.1# nslookup apigateway.system.svc.cluster.local
Server: 100.96.0.10
Address: 100.96.0.10:53
*** Can't find apigateway.system.svc.cluster.local: No answer
Name: apigateway.system.svc.cluster.local
Address: 100.96.101.242