Setting up ILS is pretty easy. Are you using this for home cluster information, global dialplan replication, or something else? Depending on the use, there are a couple of different prep steps that are recommended.
If you don't want to use TLS, you can set the two systems up with a password instead. Just be sure to uncheck the TLS checkbox.
IF your clusters already have unique Cluster IDs (very first Enterprise Parameter), then configuring ILS does not require any downtime, can be done during the production day without hurting anything (although I'd still do it off hours because I'm a safety kind of person), and no services need to be restarted after implementation.
IF your clusters do not yet have unique Cluster IDs, then those need to be changed first. The system will tell you that all services need to be restarted after this change and restarting your clusters is probably the easiest way to do that. In my experience, if ILS is the only intercluster thing you are doing then the services restart is not immediately necessary.
Here is a link to setting up ILS. If you are also doing GDPR, you will want to set those components first:
System Configuration Guide for CUCM 12.0(1) - Chapter: Configure ILS
Maren
