Validate absolute DNS name requirement on StaticDNS CNAME

[jhg03a]

I'm submitting a ...

• bug report
• new feature / enhancement request
• improvement request (usability, performance, tech debt, etc.)
• other

Traffic Control components affected ...

• CDN in a Box
• Documentation
• Grove
• Traffic Control Client
• Traffic Monitor
• Traffic Ops
• Traffic Ops ORT
• Traffic Portal
• Traffic Router
• Traffic Stats
• Traffic Vault
• unknown

Current behavior:

When I was creating a Static DNS CNAME record, I added domain.foo.com to a new DS and snapshotted.
This causes the snapshot to fail to apply with no user feedback except to go dig around in TR logs.

Expected / new behavior:

Please remove the footgun of forgetting the trailing dot in the CNAME address and better safeties to prevent it from becoming part of a snapshot.

Minimal reproduction of the problem with instructions:

1. Add a staticDNS CNAME record with address lacking the final period.
2. Snapshot
3. Observe the Snapshot fails to apply
4. Add a trailing period to the address field of record from 1.
5. Snapshot
6. Observe things work after head banging

Anything else:

WARN  2020-05-30T01:57:54.921 [New I/O worker #8] com.comcast.cdn.traffic_control.traffic_router.core.util.PeriodicResourceUpdater - 'ccr.testds.cdn.domain.com' is not an absolute name
org.xbill.DNS.RelativeNameException: 'domain.foo.com' is not an absolute name
        at org.xbill.DNS.Record.checkName(Record.java:721)
        at org.xbill.DNS.SingleNameBase.<init>(SingleNameBase.java:33)
        at org.xbill.DNS.SingleCompressedNameBase.<init>(SingleCompressedNameBase.java:23)
        at org.xbill.DNS.CNAMERecord.<init>(CNAMERecord.java:28)
        at com.comcast.cdn.traffic_control.traffic_router.core.dns.ZoneManager.addStaticDnsEntries(ZoneManager.java:703)

[ocket8888]

So is the preferred solution to make it so that a CNAME can be added without a trailing . or so that such CNAMEs would be rejected by the API?

[jhg03a]

Yes. Implementer's choice.

[jhg03a]

Or at least update the documentation with a CNAME example showing it's a requirement

[jhg03a]

Triaging silent errors, reading stack traces, and digging through 3rd party library source code to find out what "Absolute" means is not something operators can afford to be doing during an outage.

[mitchell852]

when you create a federation cname, you have to add the trailing dot. i say we keep it consistent and just require the trailing dot.

[mitchell852]

this is the error you get if you leave out the trailing dot.

org.xbill.DNS.RelativeNameException: 'foo' is not an absolute name

[mitchell852]

also, i added the bug label because missing validation feels like a bug to me.

[mitchell852]

I also changed the title @jhg03a - hope you don't mind.

[jhg03a]

Yes. Implementer's choice.

That's fine. It just needs a helpful message to go with and not just "denied"

[mitchell852]

I put the major label on this as it will block a snapshot.

[rimashah25]

@jhg03a : Does the trailing period affect only DNS type cname_record or the other 3 as well?

[jhg03a]

CNAME is where I found it. In theory it would be anywhere we specify the Dns name of a record that uses that library to validate.

[mitchell852]

fixed per #4934