Grails 3 comes with a default logback.groovy file which is bundled in war. This post shows How to externalize the logback configuration so that logback configuration can be changed without requiring a to deploy the war again.
How to configure session timeout for Grails 3 applications
Hibernate custom UserType to store field value as json string in database
Before Grails 3, it was possible to use inplace plugins by declaring grails.plugin.location. However Grails 3 projects are built using gradle and this approach no longer works. This example shows how to use inplace plugins with grails 3 using gradle multi module projects.
How to package common bases test classes in plugin jar
How to configure logback rolling file appender