# You can add additional labels to the probe results using the probe field,
# "additional_label".  An additional label's value can be static or it can be
# derived from the target labels.
#
# For the following config, probe results will look like the following:
# total{probe=google_com,ptype=http,src_zone=us-east1-c,env=prod}: 90
# success{probe=google_com,ptype=http,src_zone=us-east1-c,env=prod}: 80
probe {
    name: "google_com"
    type: HTTP
    targets {
        host_names: "www.google.com"
    }
    interval_msec: 5000
    timeout_msec: 1000

    additional_label {
      key: "src_zone"
      value: "{{.zone}}"    # It will be replaced by GCE zone if running on GCE.  
    } 

    additional_label { 
      key: "env"
      value: "prod"
    }

    http_probe {}
}
# You can add additional labels to the probe results using the probe-level field,
# "additional_label".  An additional label's value can be static or it can be
# derived from the target labels.
#
# For the following config:
#   if ingress target has label "fqdn:app.example.com",
#   and prober is running in the GCE zone "us-east1-c",
#   and proer's GCE instance has label "env:prod".
# 
# Probe results will look like the following:
#   total{probe="my_ingress",ptype="http",metrictype="prober",env="prod",src_zone="us-east1-c",host="app.example.com"}: 90
# success{probe="my_ingress",ptype="http",metrictype="prober",env="prod",src_zone="us-east1-c",host="app.example.com"}: 80
probe {
  name: "my_ingress"
  type: HTTP

  targets {
    rds_targets {
      resource_path: "k8s://ingresses"
      filter {
        key: "namespace"
        value: "default"
      }
    }
  }
  
  # Static label
  additional_label {
    key: "metrictype"
    value: "prober"
  }
  
  # Label is configured at the run time, based on the prober instance label (GCE).
  additional_label {
    key: "env"
    value: "{{.label_env}}"
  }
  
  # Label is configured at the run time, based on the prober environment (GCE).
  additional_label {
    key: "src_zone"
    value: "{{.zone}}"
  }
  
  # Label is configured based on the target labels.
  additional_label {
    key: "host"
    value: "@target.label.fqdn@"
  }

  http_probe {}
}

Enhance the additional label example.
Enhance the additional label example.