Creating alerts with external metrics

Related to #1968
I'm confused.
I want to use Kapacitor+Chronograf to make my own metrics alerts, with my own data imported. For that reason, I don't need Telegraf.
When I use my metrics to configure the alerts, the relative ones doesn't work properly, it seems Kapacitor don't consider that exist a relevant change between 1 minute ago metrics and the actual. Deadman and threshold alerts works properly.
But when I try to do the same relative alerts, with the same code, changing the db to use Telegraf, and taking cpu_usage as measurement, it works!
So this behaviour leads me to wonder if it's possible to use InfluxDB+Chronograf+Kapacitor to make alerts of my own data?
I don't think that Telegraf is necessary to import the metrics, I understand that I can do it from another place... I'm wrong?

Start by reproducing the relative-alert behavior in Kapacitor with the user's imported metrics, then compare it with the same alert using Telegraf's cpu_usage measurement. The issue names Chronograf, Kapacitor, InfluxDB, and Telegraf but no files or tests; done means determining whether external metrics are supported and identifying why relative alerts differ.

Written by the indexing model from the issue text.