Migrating from 7.1 to WildFly shouldn't be a big undertaking.

Biggest changes are related to EE 6 --> EE7 where your app might need to be updated a bit.

Beyond that, you will need to migrate configuration, if you had modified any.

Biggest changes are that web subsystem was replaced with undertow subsystem.

and messaging with messaging-activemq subsystem.

There are many guide about migration as well as some automated tools to help you.

see How do I migrate my application from AS7 to WildFly - Latest WildFly Documentation - Project Documentation Editor

https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.0/html-single/migration_guide/

GitHub - wildfly/wildfly-server-migration: A tool to migrate a WildFly server