support high cardinality tag extraction with + prefix, update conf ex…

…ample

pkg/collector/dist/datadog.yaml

@@ -139,9 +139,14 @@ metadata_collectors:
 # log_level: info
 # log_file: /var/log/datadog/agent.log
 
-# Docker
+# Docker tag extraction
+#
+# We can extract container label or environment variables
+# as metric tags. If you prefix your tag name with +, it
+# will only be added to high cardinality metrics (docker check)
 #
 # docker_labels_as_tags:
-#   - label_name
+#   label_name:             tag_name
+#   high_cardinality_label: +tag_name
 # docker_env_as_tags:
-#   - ENVVAR_NAME
+#   ENVVAR_NAME: tag_name

pkg/tagger/collectors/docker_extract.go

@@ -41,7 +41,11 @@ func (c *DockerCollector) extractFromInspect(co types.ContainerJSON) ([]string,
 	if len(c.labelsAsTags) > 0 {
 		for label_name, label_value := range co.Config.Labels {
 			if tag_name, found := c.labelsAsTags[strings.ToLower(label_name)]; found {
-				low = append(low, fmt.Sprintf("%s:%s", tag_name, label_value))
+				if tag_name[0] == '+' {
+					high = append(high, fmt.Sprintf("%s:%s", tag_name[1:], label_value))
+				} else {
+					low = append(low, fmt.Sprintf("%s:%s", tag_name, label_value))
+				}
 			}
 		}
 	}
@@ -53,7 +57,11 @@ func (c *DockerCollector) extractFromInspect(co types.ContainerJSON) ([]string,
 				continue
 			}
 			if tag_name, found := c.envAsTags[strings.ToLower(parts[0])]; found {
-				low = append(low, fmt.Sprintf("%s:%s", tag_name, parts[1]))
+				if tag_name[0] == '+' {
+					high = append(high, fmt.Sprintf("%s:%s", tag_name[1:], parts[1]))
+				} else {
+					low = append(low, fmt.Sprintf("%s:%s", tag_name, parts[1]))
+				}
 			}
 		}
 	}