Support domain resolution to obtain the nameserver address

[lizhimins]

Currently, the address of the NameServer is resolved in the form of splitting ";".
In the k8s environment, we can deploy it in single deployment.
We need to support domain resolution to obtain the NameServer address.

目前对 NameServer 的地址是以分割 ";" 的形式进行解析的，在 k8s 环境中，由于 NameServer 水平对等无状态，我们可以采用 deployment 的形式部署，需要支持域名解析来获取地址。

[lizhanhui]

Though this is a very commonly used technique, shared by many popular products, say grpc, envoy. This feature is pretty tricky for Java applications because Java has a lot of related bugs, which may impact this feature negatively if JDK is not carefully chosen
To name a few
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=6247501
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8274692

[lizhimins]

I make this feature optional and off by default, and emphasize the points needing attention in the config. Users need to understand its side effects when they enable a feature-gate like k8s.

[lizhimins]

@RongtongJin @odbozhou @dongeforever Do you have a better idea?

[xdkxlk]

Though this is a very commonly used technique, shared by many popular products, say grpc, envoy. This feature is pretty tricky for Java applications because Java has a lot of related bugs, which may impact this feature negatively if JDK is not carefully chosen To name a few https://bugs.java.com/bugdatabase/view_bug.do?bug_id=6247501 https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8274692

How did grpc-java solve this kind of problem?

[lizhimins]

How did grpc-java solve this kind of problem?

grpc use InetAddress.getAllByName(host) to get list

[lizhimins]