UndertowWebServerFactoryCustomizer can map properties from: - server.undertow.options.server.* - server.undertow.options.socket.* into: - builder.setSocketOption(...) - builder.setSocketOption(...)

but it does not support org.xnio.Options but only UndertowOptions, see: https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/UndertowWebServerFactoryCustomizer.java#L141

To use builder.setSocketOption(...) we need properties from org.xnio.Options.

Comment From: wilkinsona

Thanks for the report. This looks like a bug to me. As far as I can tell, none of the options on UndertowOptions is intended for use as a socket option. This means that the server.undertow.options.socket.* properties are of no use as currently implemented.