I’d like to be able to display an alert on all connected clients when my server is having trouble accessing an external API. Is there a way to register a single javascript object that can be referenced reactively by client-side templates? I could use a collection that holds just a single entry but that doesn’t seem quite right. I’ve looked at ReactiveVars but they seem to be just client-side. Any other options?
Thanks a lot!
Personally, I think using collection is the fiine. Later you might need other messages passing through. So a collection can serve that purpose. 
If you want to notify all connected clients, you can implement a publish() method using null as the name.
See also here.
The data published can come from a collection (typically CollectionName.find(...)), or you can generate publication data yourself in the publish() method by using this.added(), this.changed(), this.removed() and this.ready().