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incorrect-CNAME-mapping

Incorrect CNAME Mapping​

Overview​

This article explains a common issue where DNS resolution fails due to incorrect CNAME record configuration, particularly when a wildcard is used in the CNAME target.

Symptom​

When attempting to access an endpoint, you may encounter a resolution error.

HTTP Error:

HTTP GET on resource 'https://api.techworld360.io:443/api/v1/endpoint/' failed: Couldn't resolve address.

cURL Error:

$ curl -v api.techworld360.io
* Could not resolve host: api.techworld360.io
* Closing connection
curl: (6) Could not resolve host: api.techworld360.io

Cause​

This issue is usually due to a misconfigured DNS CNAME record. Specifically, using a wildcard domain (e.g., *.ipaddress.technet360.io) as the CNAME target for a subdomain is not valid in most DNS resolvers.

Example of incorrect configuration: api.techworld360.io → CNAME → *.ipaddress.technet360.io

Some DNS resolvers and libraries (including certain versions of cURL) do not support CNAME records that resolve to wildcard domains. Consequently, the name resolution chain breaks.

How to Verify​

You can use standard DNS resolution tools to check the CNAME chain. For example, using dig:

$ dig api.techworld360.io

api.techworld360.io.   60  IN  CNAME   *.ipaddress.technet360.io.
*.ipaddress.technet360.io.  60  IN  A       10.0.7.21
*.ipaddress.technet360.io.  60  IN  A       10.0.7.22

[!IMPORTANT] The presence of a wildcard (*) in the CNAME target (the right-hand side) indicates an invalid configuration.

Solution​

Update the DNS CNAME record to use a specific, Fully Qualified Domain Name (FQDN) without a wildcard.

  • ❌ Incorrect: api.techworld360.io → *.ipaddress.technet360.io
  • ✅ Correct: api.techworld360.io → ipaddress.technet360.io
  • ✅ Correct: *.techworld360.io → ipaddress.technet360.io

This ensures compatibility across all standard DNS resolvers and clients.