When using ExternalDNS on Google Cloud DNS, unexpected behavior can occur due to how TXT records are managed. By default, ExternalDNS creates a TXT record for each DNS entry, attempting to manage records like a-staging.example.com, which can lead to errors when no corresponding Managed Zone exists. This happens because each subdomain must have its own Managed Zone for independent handling. To avoid confusion and ensure correct management, it is necessary to configure the flags --txt-owner-id and --txt-prefix effectively.
ExternalDNS uses a mechanism called the TXT registry for managing ownership of DNS records, creating a TXT record for each managed DNS entry.
The default TXT registry logic substitutes %{record_type} and uses a prefix of a-, leading to attempts to manage records like a-staging.example.com which lack corresponding zones.
When managing apex domains like staging.example.com in Google Cloud DNS, each subdomain requires its own Managed Zone for independent management.
Using the flags --txt-owner-id and --txt-prefix can resolve mysterious DNS behaviors when deploying ExternalDNS on GCP.
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