Enable the "Wildcard mode > Match_latest_modified" setting, found in the "File properties" section.
There are two ways to design the FKM to look in the latest file, these are:
First, if your today file contains today's date, then you can use the today function. E.g.
Second, you may just input a wildcard at the end of siteserver. E.g.
This will monitor the siteserver*.log file that has the latest "changed time" timestamp. A note on the changed time as described in the FKM reference guide:
You may also use the last modified time. Just alter the Wildcard match time setting in the FKM sampler's advanced tab and choose "Modified".
In addition, when using the wildcard approach, kindly ensure that the setting Wildcard monitor all matches is not ticked (unchecked) or greyed out. If the said setting is ticked (checked), FKM will monitor all files that starts with siteserver and ends with .log. The said setting can also be found in the FKM sampler's advanced tab.