coredns.io/content/blog/when-external.md

+++ date = "2017-07-23T22:00:00Z" description = "When should middleware be external?" tags = ["Middleware", "External", "Out-of-Tree"] title = "When Should Middleware be External?" author = "miek" +++

The middleware.md in the CoreDNS source tree has some pointers on what a middleware for CoreDNS should have as minimum requirements. It basically boils down to: documentation, tests and working.

It is easier to list when a middleware can be included in CoreDNS than to say it should stay external, so we will do the first:

• First, the middleware should be useful for other people. "Useful" is a subjective term, but the middleware needs to fill a niche that appeals to more than one person.
• It should be sufficiently different from other middleware to warrant inclusion.
• Current internet standards need be supported: IPv4 and IPv6, so A and AAAA records should be handled (if your middleware is in the business of dealing with address records that is).
• It must have tests.
• It must have a README.md for documentation.

Middleware for CoreDNS can live out-of-tree, middleware.cfg defaults to CoreDNS' repo but other repos work just as well, so it is pretty easy to use your middleware even though it is out-of-tree.