web applications definitions syncing between primary and backup nodes

Yes, it's normal, Web Applications are local configuration on each mirror member.

If/when you create a new Web Application you need to create it in all mirror members. Personally I prefer to create the application using a script (a class method) that is deployed and run (typically along with code etc.) in all members nodes.

In addition to Web Applications note that also all security related configuration (Users, Roles, Resources, SQL privileges etc.) are local to each mirror member.

It's my understanding that InterSystems is working on enhancing the mirror to include security configuration synchronization (Web Applications are part of the Security) between mirror member.

Until such time as InterSystems provides synchronization for security components across mirror members, you can save a bit of effort by exporting them on the primary and importing them on the alternate server via the ^SECURITY routine in the %SYS namespace. At least you won't need to create them manually.

You can do the same for users, roles, resources and a few other things as well. All of these have ObjectScript methods for accomplishing the same in the Security package.

Another solution is to use Deltanji source control to manage and transfer these items, as this has the added benefit of providing full source control and accountability of changes to these items. I know you’re getting set up with Deltanji at the moment with John, so this is something he can help you with.