[jira] [Created] (HADOOP-18087) fix bug in handling CNAME chain records

["YUBI LEE (Jira)" <ji...@apache.org>]

YUBI LEE created HADOOP-18087:
---------------------------------

             Summary: fix bug in handling CNAME chain records
                 Key: HADOOP-18087
                 URL: https://issues.apache.org/jira/browse/HADOOP-18087
             Project: Hadoop Common
          Issue Type: Bug
          Components: registry
    Affects Versions: 3.1.2
            Reporter: YUBI LEE


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)


{code}
$ 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
{code}

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.


{code:java}
    // 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;
{code}





It should be like this:

{code}
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
{code}

I will make a pull request at https://github.com/apache/hadoop soon.





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