Name resolution of a backends host name is done at start up, or configuration reload. If “dns” is true, name resolution takes place dynamically. This is useful if a backends address changes frequently. If “dns” is true, name resolution of a backend’s host name at start up, or configuration reload is skipped. Please see https://nghttp2.org/documentation/nghttpx.1.html#cmdoption-nghttpx-b for more detail.

false