1 - Create a new datasource through web admin console 2 - When in final step, click to test the connection 3 - Even it being a test it seems that it tries to add the datasource, so if you try to test again you'll get: Unexpected HTTP response: 500 Request { "name" => "MySqlDS" , "use-ccm" => false , "pool-name" => "MySqlDS_Pool" , "connection-url" => "jdbc:mariadb: //192.168.0.119:3306" , "jta" => false , "driver-class" => "org.mariadb.jdbc.Driver" , "driver-name" => "mariadb-java-client-1.3.4.jar" , "valid-connection-checker-class-name" => "org.jboss.jca.adapters.jdbc.extensions.mysql.MySQLValidConnectionChecker" , "background-validation" => true , "exception-sorter-class-name" => "org.jboss.jca.adapters.jdbc.extensions.mysql.MySQLExceptionSorter" , "jndi-name" => "java:/MySqlDS" , "user-name" => "root" , "password" => "123" , "enabled" => true , "operation" => "add" , "address" => [ ( "subsystem" => "datasources" ), ( "data-source" => "MySqlDS" ) ] } Response Internal Server Error { "outcome" => "failed" , "failure-description" => "WFLYCTL0158: Operation handler failed: org.jboss.msc.service.DuplicateServiceException: Service org.wildfly.data-source.MySqlDS is already registered" , "rolled-back" => true , "response-headers" => { "process-state" => "reload-required" } } 01:52:14,722 ERROR [org.jboss.as.controller.management-operation] (XNIO-3 task-10) WFLYCTL0013: Operation ( "add" ) failed - address: ([ ( "subsystem" => "datasources" ), ( "data-source" => "MySqlDS" ) ]): org.jboss.msc.service.DuplicateServiceException: Service org.wildfly.data-source.MySqlDS is already registered