Architecture

The repository contains 4 distinct parts in subdirectories:

• api the record editing API server
• client Go client for the record editing API
• coredns customized CoreDNS build
• external-dns webhook for usage with External DNS operator

API server and client

The api/openapi.yaml file contains an OpenAPI specification for the record editing API used by the API server and client. Both the server and client are tested against this specification.

The API server manages record overrides. On each DNS query, CoreDNS communicates with the API server with gRPC to query for record overrides. CoreDNS then returns the overridden record if there is one.

CoreDNS

CoreDNS is used as the DNS server being queried by users. It is separate from the API server to allow for operation without the API server, and for operating multiple DNS servers from the same API server (for example one server with ad-blocking and one without).

The coredns/plugin/filterlist directory contains the CoreDNS plugin implementing ad-blocking logic.

The coredns/plugin/injector directory contains the CoreDNS plugin implementing lookups in the API server over gRPC.

External DNS webhook

The external-dns directory contains a webhook for External DNS operator. This webhook uses the API client to automatically update DNS records for services running on Kubernetes.

Using External DNS, multiple clusters can automatically update DNS records in the API server seamlessly.