eubnara opened a new pull request, #8091:
URL: https://github.com/apache/hadoop/pull/8091
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### 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.
```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;
```
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:
- [x] 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](http://www.apache.org/legal/resolved.html#category-a)?
- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
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