DNS check fails for CNAME records

[danvaida]

Output of the info page (if this is a bug)
Log entry:

2021-11-03 15:33:39 CET | CORE | ERROR | (pkg/collector/python/datadog_agent.go:116 in LogMessage) | dns_check:xyz-dns-check:95e92da93d0a5f5b | (dns_check.py:108) | DNS resolution of xyz.domain.com has failed.
Traceback (most recent call last):
  File "/opt/datadog-agent/embedded/lib/python2.7/site-packages/datadog_checks/dns_check/dns_check.py", line 97, in check
    self._check_answer(answer, resolves_as)
  File "/opt/datadog-agent/embedded/lib/python2.7/site-packages/datadog_checks/dns_check/dns_check.py", line 121, in _check_answer
    ips = [x.strip().lower() for x in resolves_as.split(',')]
AttributeError: 'list' object has no attribute 'split'

$ sudo datadog-agent status
Getting the status from the agent.

===============
Agent (v6.19.2)
===============

  Status date: 2021-11-03 15:39:01.306857 CET
  Agent start: 2021-11-03 13:40:46.309635 CET
  Pid: 28111
  Go Version: go1.13.8
  Python Version: 2.7.17
  Build arch: amd64
  Check Runners: 4
  Log Level: info
[...]
  Host Info
  =========
    bootTime: 2021-11-02 17:10:20.000000 CET
    kernelVersion: 3.10.0-957.5.1.el7.x86_64
    os: linux
    platform: centos
    platformFamily: rhel
    platformVersion: 7.6.1810
    procs: 196
    uptime: 20h30m27s
[...]
dns_check (1.5.2)
    -----------------
      Instance ID: dns_check:xyz-dns-check:95e92da93d0a5f5b [OK]
      Configuration Source: file:/etc/datadog-agent/conf.d/dns_check.d/conf.yaml
      Total Runs: 473
      Metric Samples: Last Run: 0, Total: 0
      Events: Last Run: 0, Total: 0
      Service Checks: Last Run: 1, Total: 473
      Average Execution Time : 2ms
      Last Execution Date : 2021-11-03 15:38:54.000000 CET
      Last Successful Execution Date : 2021-11-03 15:38:54.000000 CET

Describe what happened:
Check is unable to resolve the record.

Describe what you expected:
Check is able to resolve the record.

Steps to reproduce the issue:
Try to resolve a CNAME record.

$ cat /etc/datadog-agent/conf.d/dns_check.d/conf.yaml
init_config: {}
instances:
  - hostname: xyz.domain.com
    name: xyz-dns-check
    resolves_as: "1.1.1.1"
    tags: 
      - "team:erp"

Additional environment details (Operating System, Cloud provider, etc):

Haven't had the chance yet to try and reproduce this on the latest version.

[ChristineTChen]

Hi @danvaida, the resolves_as config option takes a comma separated string.

Also I think there may be some yaml issues with your conf.yaml, it's missing an instances key. Please try to following and let me know if that resolves the error.

init_config: {} # assuming no changes were made for the `init_config`

instances:
  - hostname: xyz.domain.com
    name: xyz-dns-check
    resolves_as: "1.1.1.1"
    tags: 
      - "team:erp"

[danvaida]

Hi @ChristineTChen,

it's missing an instances key.

I think it must've been a copy-paste error on my behalf... the file that I have is actually identical in terms of structure with what you posted. The content of the log entry and status message prove this. I updated my original snippet in this issue, now.

[ChristineTChen]

@danvaida error log line is saying it can't split the resolves_as value by ,. If you fixed the resolves_as value in the dns_check's conf.yaml, please try restarting the Agent and running the check if you still see the error.

Otherwise, I would need more information from your Agent. Please open a support ticket and submit a flare if the above does not resolve your issue. Thank you!

[danvaida]

As said, the data is already in the right format, yet the error persists, regardless of restarts.
Will open an internal support ticket from now on...