knot-resolver 3.2.1-3ubuntu2.1 (amd64 binary) in ubuntu focal

 The Knot DNS Resolver is a caching full resolver implementation
 written in C and LuaJIT, including both a resolver library and a
 daemon. Modular architecture of the library keeps the core tiny and
 efficient, and provides a state-machine like API for
 extensions. There are three built-in modules - iterator, cache,
 validator, and many external.
 .
 The Lua modules, switchable and shareable cache, and fast FFI
 bindings makes it great to tap into resolution process, or be used
 for your recursive DNS service. It's the OpenResty of DNS.
 .
 The server adopts a different scaling strategy than the rest of the
 DNS recursors - no threading, shared-nothing architecture (except
 MVCC cache that may be shared). You can start and stop additional
 nodes depending on the contention without downtime.