There can be multiple DNS resource records for a given name. They can
vary by type, ttl, rrdata and a number of various other parameters. It
is incorrect to return a single resource record for a given name.
This change updates the Get interface to return multiple records for a given
name and uses this list in the federated service controller to perform
DNS operations.
This will allow us to pass e.g. a ResourceRecordChangeset, rather than a
ResourceRecordChangeset, the parent ResourceRecordSets, and the
grandparent Zone.
Laying the groundwork for simplifying / optimizing the federation logic.
Although Google Cloud DNS requires strict add & remove calls, most
dnsproviders actually support upsert, and an add & remove is much more
expensive (primarily because of the need to fetch the pre-image).
Add support for 'upsert' operations, which don't require the pre-image,
and simply overwrite the existing record. This is much cheaper on
Amazon Route53, for example.
Madhusudan.C.S