dnscontrol/docs/_functions/domain/IMPORT_TRANSFORM.md

name	parameters
IMPORT_TRANSFORM	transform table domain modifiers...

Don't use this feature. It was added for a very specific situation at Stack Overflow.

IMPORT_TRANSFORM adds to the domain all the records from another domain, after making certain transformations and resetting the TTL.

Example:

Suppose foo.com is a regular domain. bar.com is a regular domain, but certain records should be the same as foo.com with these exceptions: "bar.com" is added to the name, the TTL is changed to 300, if the IP address is between 1.2.3.10 and 1.2.3.20 then rewrite the IP address to be based on 123.123.123.100 (i.e. .113 or .114).

You wouldn't want to maintain bar.com manually, would you? It would be very error prone. Therefore instead you maintain foo.com and let IMPORT_TRANSFORM automatically generate bar.com.

{% capture example %}

foo.com:
    one.foo.com.    IN A 1.2.3.1
    two.foo.com.    IN A 1.2.3.2
    three.foo.com.  IN A 1.2.3.13
    four.foo.com.   IN A 1.2.3.14

bar.com:
    www.bar.com.    IN 123.123.123.123
    one.foo.com.bar.com.    IN A 1.2.3.1
    two.foo.com.bar.com.    IN A 1.2.3.2
    three.foo.com.bar.com.  IN A 123.123.123.113
    four.foo.com.bar.com.   IN A 123.123.123.114

{% endcapture %}

{% include example.html content=example %}

Here's how you'd implement this in DNSControl:

{% capture example %}

var TRANSFORM_INT = [
    // RANGE_START, RANGE_END, NEW_BASE
    { low: "1.2.3.10", high: "1.2.3.20", newBase: "123.123.123.100" },  //   .10 to .20 rewritten as 123.123.123.100+IP
    { low: "2.4.6.80", high: "2.4.6.90", newBase: "123.123.123.200" },  //   Another rule, just to show that you can have many.
]

D("foo.com", .... ,
  A("one","1.2.3.1")
  A("two","1.2.3.2")
  A("three","1.2.3.13")
  A("four","1.2.3.14")
);

D("bar.com", .... ,
  A("www","123.123.123.123")
  IMPORT_TRANSFORM(TRANSFORM_INT, 'foo.com', 300),
);

{% endcapture %}

{% include example.html content=example %}

Transform rules are: RANGE_START, RANGE_END, NEW_BASE. NEW_BASE may be:

• An IP address. Rebase the IP address on this IP address. Extract the host part of the /24 and add it to the "new base" address.
• A list of IP addresses. For each A record, inject an A record for each item in the list: newBase: ['1.2.3.100', '2.4.6.8.100'] would produce 2 records for each A record.