merged to release-8.x

Agreed. I'm trying to standarize those functions between datasources and allow them to accept either Node id or FS:FSID. 

Luckly there are not too many that accept arguments. I'm hoping to have the soled this sprint. I have a couple of PR's related   and for now. I'm just investigating more on to ensure that I'm handling the arguments correctly.

: https://github.com/OpenNMS/opennms-helm/pull/489

: https://github.com/OpenNMS/opennms-helm/pull/491

You're right, the problem is that the label contains characters not allowed by the regex, but $node in this case is an FS:FSID returned from nodeFilter(). We're tripping over ourselves and preventing data returned from our own template variables from being used consistently in other fields in the datasource. It may not have the same root cause or solution, but it is a symptom of the same problem.

that error seems to be related to the actual foreign Source ID or name that doesn't match the regex . I tried to replicate but I'm not familiar with this expressions but I could not find any issue with the actual FS:FSID template variable passed to the label. They seemd to work for me. But I was only able to use expressions with constant values (like I said I'm not familiar with the expresions syntax, and the documentation didn't have any examples).

Maybe we can create a separate Jira and some steps to be able to reproduce since is different from fix I have found for this actual case.
[a-zA-Z_$]+[0-9a-zA-Z_$]*

Peripherally related: In the case when a user needs unique Labels on a dynamic dashboard, I learned today that one also cannot pass an FS:FSID (from the form of a template variable $node = nodeFilter(...)) into an Expression, either:

I think this example encapsulates the user frustrations.