Learning CoreDNS

Chapter 7. Manipulating Queries and Responses

CoreDNS gives you a great deal of control over what happens to a request as it goes through the plug-in chain, and what response is provided to the client. This allows you to tailor the DNS behavior to your particular environment and use cases. For example, you can easily generate standard names within specific zones using the template plug-in, and you can transparently redirect traffic using the rewrite plug-in.

This chapter discusses a few of the most commonly used plug-ins for manipulating requests and responses in this way.

The template Plug-in

The template plug-in allows you to fabricate answers based solely upon the request. A common use case for this is the creation of answers to PTR queries, without having to actually write them all out in a zone file, as shown in Example 7-1.¹

Example 7-1. Answering PTR queries with template

 example.com:5300 in-addr.arpa:5300 {     # Match host-a-b-c-d.example.com A requests and return a.b.c.d     template IN A example.com {       match (^|[.])host-(?P<a>[0-9]*)-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)↵       [.]example[.]com[.]$       answer "{{ .Name }} 60 IN A {{ .Group.a }}.{{ .Group.b }}.{{ .Group.c }}.↵       {{ .Group.d }}"       fallthrough     }     # Match d.c.b.a.in-addr.arpa PTR requests and return host-a-b-c-d.example.com     template IN PTR in-addr.arpa {       match ^(?P<d>[0-9]*)[.](?P<c>[0-9]*)[.](?P<b>[0-9]*)[.](?P<a>[0-9]*)↵       [.]in-addr[.]arpa[.]$       answer "{{ ...