In previous versions of EAP (Web subsystem) there was possible to enable resolving hosts for access logging. This is not possible to enable with Undertow.
Steps for enabling in JBoss Web:
This was accomplished by setting resolve-hosts attribute of access-log to true (/subsystem=web/virtual-server=default-host/configuration=access-log:add(resolve-hosts=true)) and enabling lookups for connector (/subsystem=web/connector=http:write-attribute(name=enable-lookups, value=true)).
In Undertow subsystem there is only possible to enable resolving peer address (/subsystem=undertow/server=default-server/http-listener=default:write-attribute(name=resolve-peer-address, value=true)), which doesn't have by itself any impact on output in access-log