Ceph plugins

Hello, according to the ceph documentation, when implementing a new ceph plugin there are three functions that are important to override: as shown in the documentation: " The most important methods to override are: a serve member function for server-type modules. This function should block forever. a notify member function if your module needs to take action when new cluster data is available. a handle_command member function if your module exposes CLI commands. " It is not very clear to me what is the difference between the serve method and the handle_command. when do I use one or another? can someone please explain this a little further Thanks