Added label_key option for counters

README.md

@@ -232,6 +232,7 @@ For details of each metric type, see [Prometheus documentation](http://prometheu
   type counter
   desc The total number of foo in message.
   key foo
+  label_key bar
   <labels>
     tag ${tag}
     host ${hostname}
@@ -244,10 +245,21 @@ For details of each metric type, see [Prometheus documentation](http://prometheu
 - `type`: metric type (required)
 - `desc`: description of this metric (required)
 - `key`: key name of record for instrumentation (**optional**)
+- `label_key`: key name of record with label values (optional)
 - `<labels>`: additional labels for this metric (optional). See [Labels](#labels)
 
 If key is empty, the metric values is treated as 1, so the counter increments by 1 on each record regardless of contents of the record.
 
+If label_key is specified, a label with that name will be added with the value from the record. If the value is an array,
+a counter for each value is incremented. E.g. if you have `label_key exeception` and a record with `record['exception'] = ['MQException', 'InvalidDestinationException']`, you will get these metrics:
+
+```
+metric_name{exception="MQException"} 1.0
+metric_name{exception="InvalidDestinationException"} 1.0
+```
+
+Other labels will be added as specified.
+
 ### gauge type
 
 ```

fluent-plugin-prometheus.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |spec|
   spec.name          = "fluent-plugin-prometheus"
-  spec.version       = "1.0.1"
+  spec.version       = "1.1.0"
   spec.authors       = ["Masahiro Sano"]
   spec.email         = ["[email protected]"]
   spec.summary       = %q{A fluent plugin that collects metrics and exposes for Prometheus.}

lib/fluent/plugin/prometheus.rb

@@ -144,6 +144,7 @@ def instrument(record, expander, placeholders)
       class Counter < Metric
         def initialize(element, registry, labels)
           super
+          @label_key = element['label_key']
           begin
             @counter = registry.counter(element['name'].to_sym, element['desc'])
           rescue ::Prometheus::Client::Registry::AlreadyRegisteredError
@@ -158,7 +159,14 @@ def instrument(record, expander, placeholders)
           # ignore if record value is nil
           return if value.nil?
 
-          @counter.increment(labels(record, expander, placeholders), value)
+          if @label_key
+            # add label from record
+            Array(record[@label_key]).each do |label_value|
+              @counter.increment(labels(record, expander, placeholders).merge(@label_key.to_sym => label_value), value)
+            end
+          else
+            @counter.increment(labels(record, expander, placeholders), value)
+          end
         end
       end