relabel_configs voodoo

[agardnerIT]

I understand that relabel_configs works, but I don't know why. I don't understand what this section does, why it's necessary? It's just "magic". Can someone help me understand?

If I run without that section, I get:

err="parsing YAML file prometheus.yml: \"http://localhost:12000\" is not a valid hostname"

So it's doing something important - but it isn't documented anywhere?