WildFly outputs the Undertow version logging at start-up and stop of the undertow server in the subsystem layer. For example:

15:53:54,139 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-2) WFLYUT0003: Undertow 2.0.26.Final starting
...(snip)...
15:54:39,589 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-5) WFLYUT0004: Undertow 2.0.26.Final stopping

So far, so good.

However, when Undertow is embedded in an application that uses io.undertow.Undertow API (e.g. Spring Boot application using Undertow as an embedded web server), no undertow version information is logged at the start-up. Even if the logging level is set to DEBUG, no undertow version information is output:

2019-10-15 10:45:15.895 DEBUG 19108 --- [           main] io.undertow                              : starting undertow server io.undertow.Undertow@508c61aa
2019-10-15 10:45:15.906  INFO 19108 --- [           main] org.xnio                                 : XNIO version 3.3.8.Final
2019-10-15 10:45:15.918  INFO 19108 --- [           main] org.xnio.nio                             : XNIO NIO Implementation Version 3.3.8.Final

I would like to propose to change to output the version information at the INFO level logging in io.undertow.Undertow#start() and io.undertow.Undertow#stop().
WildFly does not use the io.undertow.Undertow API, so this change does not have a bad effect (e.g. outputting the version information twice) on WildFly.