RFC: Filter by metadata labels

[jgriff]

Summary

Add support for filtering resources with a --selector (ie, metadata labels).

This would add a new selector option to the source filter configuration:

source:
  filter:
    selector: app=my-app

Any valid value for kubectl's --selector option can be specified here, including equality (=, ==, !=) and set-based requirements (in (...), notin (...)).

Examples

Single Label Match

source:
  filter:
    selector: environment=production

Multiple Label Match

source:
  filter:
    selector: environment=production,tier=frontend

Set-based Requirements

source:
  filter:
    selector: environment in (development,production),tier in (frontend)

Negative Matches

source:
  filter:
    selector: environment!=production

source:
  filter:
    selector: environment,environment notin (production)

Combining Styles

source:
  filter:
    selector: environment=production,tier in (frontend,backend)