Add an interface:"all" tag to the net protocol counters

fixes #508

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 ### Bugfixes
 - [#506](https://github.com/influxdb/telegraf/pull/506): Ping input doesn't return response time metric when timeout. Thanks @titilambert!
+- [#508](https://github.com/influxdb/telegraf/pull/508): Fix prometheus cardinality issue with the `net` plugin
 
 ## v0.10.0 [2014-01-12]
 

plugins/inputs/system/net.go

@@ -94,7 +94,10 @@ func (s *NetIOStats) Gather(acc inputs.Accumulator) error {
 			fields[name] = value
 		}
 	}
-	acc.AddFields("net", fields, nil)
+	tags := map[string]string{
+		"interface": "all",
+	}
+	acc.AddFields("net", fields, tags)
 
 	return nil
 }

plugins/inputs/system/net_test.go

@@ -80,7 +80,10 @@ func TestNetStats(t *testing.T) {
 		"udp_noports":     int64(892592),
 		"udp_indatagrams": int64(4655),
 	}
-	acc.AssertContainsTaggedFields(t, "net", fields2, make(map[string]string))
+	ntags = map[string]string{
+		"interface": "all",
+	}
+	acc.AssertContainsTaggedFields(t, "net", fields2, ntags)
 
 	acc.Points = nil