HADOOP-18087. fix bug when getting CNAME chain records and no record from remote dns server

[eubnara]

Description of PR

When query A record which is chained by CNAME, YARN Registry DNS Server does not properly respond. Some CNAME records are missing.

For example, "repo.maven.apache.org" is chaned as follows:

repo.maven.apache.org. 21317 IN CNAME repo.apache.maven.org.
repo.apache.maven.org. 20114 IN CNAME maven.map.fastly.net.
maven.map.fastly.net. 7 IN A 199.232.192.215
maven.map.fastly.net. 7 IN A 199.232.196.215

If ask A record for "repo.maven.apache.org" using "dig" or "nslookup", YARN Registry DNS Server will give answers similar to this:
(10.1.2.3, 10.8.8.8 IP is virtual)

$ nslookup repo.maven.apache.org 10.1.2.3
Server:		10.1.2.3
Address:	10.1.2.3#53

Non-authoritative answer:
repo.maven.apache.org	canonical name = repo.apache.maven.org.
Name:	maven.map.fastly.net
Address: 151.101.196.215
** server can't find repo.apache.maven.org: NXDOMAIN

The reason why you can see "NXDOMAIN", "nslookup" will query "A" & "AAAA" records.
If there is no answer from other dns server, "answers == null" but YARN Registry DNS Server has a bug. There is no null handling.

    // Forward lookup to primary DNS servers
    Record[] answers = getRecords(name, type);
    try {
      for (Record r : answers) {
        if (!response.findRecord(r)) {
          if (r.getType() == Type.SOA) {
            response.addRecord(r, Section.AUTHORITY);
          } else {
            response.addRecord(r, Section.ANSWER);
          }
        }
        if (r.getType() == Type.CNAME) {
          Name cname = r.getName();
          if (iterations < 6) {
            remoteLookup(response, cname, type, iterations + 1);
          }
        }
      }
    } catch (NullPointerException e) {
      return Rcode.NXDOMAIN;
    } catch (Throwable e) {
      return Rcode.SERVFAIL;
    }
    return Rcode.NOERROR;

It should be like this:

nslookup repo.maven.apache.org 10.8.8.8
Server:		10.8.8.8
Address:	10.8.8.8#53

Non-authoritative answer:
repo.maven.apache.org	canonical name = repo.apache.maven.org.
repo.apache.maven.org	canonical name = maven.map.fastly.net.
Name:	maven.map.fastly.net
Address: 151.101.196.215

How was this patch tested?

• apply this patch to YARN Registry DNS Server in our cluster & test with dig and nslookup

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 58s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	32m 28s		trunk passed
+1 💚	compile	22m 47s		trunk passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	compile	19m 33s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	0m 40s		trunk passed
+1 💚	mvnsite	0m 47s		trunk passed
+1 💚	javadoc	0m 45s		trunk passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	javadoc	0m 43s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	1m 3s		trunk passed
+1 💚	shadedclient	20m 42s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 22s		the patch passed
+1 💚	compile	21m 31s		the patch passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	javac	21m 31s		the patch passed
+1 💚	compile	19m 30s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	19m 30s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 39s		the patch passed
+1 💚	mvnsite	0m 46s		the patch passed
+1 💚	javadoc	0m 44s		the patch passed with JDK Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04
+1 💚	javadoc	0m 43s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	1m 12s		the patch passed
+1 💚	shadedclient	21m 14s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	1m 30s	/patch-unit-hadoop-common-project_hadoop-registry.txt	hadoop-registry in the patch passed.
+1 💚	asflicense	0m 59s		The patch does not generate ASF License warnings.
		172m 39s

Reason	Tests
Failed junit tests	hadoop.registry.server.dns.TestRegistryDNS
	hadoop.registry.server.dns.TestSecureRegistryDNS

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3911/1/artifact/out/Dockerfile
GITHUB PR	#3911
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux 59668e60685d 4.15.0-65-generic #74-Ubuntu SMP Tue Sep 17 17:06:04 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / e20271e
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.13+8-Ubuntu-0ubuntu1.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3911/1/testReport/
Max. process+thread count	610 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-registry U: hadoop-common-project/hadoop-registry
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3911/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[steveloughran]

do we have someone who understands DNS well enough to review this?

[eubnara]

@steveloughran
Why close this issue?
YARN Registry DNS is not maintained anymore?

[steveloughran]

sorry, hadn't meant to press the close button, just the comment one

can you submit a new PR?

[eubnara]

I made new PR at #3935