Does ehcache 3.8.1 no longer automatically pick up the configuration settings in an ehcache.xml file at the source root directory?
Yes, it's looks so, now it needs to be done using a XML file by configuringe a CacheManager at creation time, according to this schema definition.
XML programmatic parsing
If you are obtaining your CacheManager through the JSR-107 API, what follows is done automatically when invoking
javax.cache.spi.CachingProvider.getCacheManager(java.net.URI, java.lang.ClassLoader)
final URL myUrl = getClass().getResource("/configs/docs/getting-started.xml");
XmlConfiguration xmlConfig = new XmlConfiguration(myUrl);
CacheManager myCacheManager = CacheManagerBuilder.newCacheManager(xmlConfig);
myCacheManager.init();
org.ehcache.config.builders.CacheManagerBuilder.newCacheManager(org.ehcache.config.Configuration)
allows you to create your CacheManager instance using the Configuration from the XmlConfiguration
Reference - http://www.ehcache.org/documentation/3.8/xml.html