added additional custom labels support for the metrics

Author: Athishpranav2003

README.md

@@ -23,6 +23,10 @@ $ gem install fluent-plugin-throttle
   group_bucket_period_s   60
   group_bucket_limit    6000
   group_reset_rate_s     100
+  <labels>
+    key1 value1
+    key2 value2
+  <labels>
 </filter>
 ```
 
@@ -137,6 +141,31 @@ When a group reaches its limit, metrics will be emitted for the logs being dropp
 Metrics for the filter is
 - `fluentd_throttle_rate_limit_exceeded`
 
+## Labels
+
+See [Prometheus Data Model](http://prometheus.io/docs/concepts/data_model/) first.
+
+You can add labels with static value or dynamic value from records. In `prometheus_monitor` input plugin, you can't use label value from records.
+
+### labels section
+
+```
+<labels>
+  key1 value1
+  key2 value2
+</labels>
+```
+
+All labels sections has same format. Each lines have key/value for label.
+
+You can use placeholder for label values. The placeholders will be expanded from reserved values and records.
+If you specify `${hostname}`, it will be expanded by value of a hostname where fluentd runs.
+
+Reserved placeholders are:
+
+- `${hostname}`: hostname
+- `${worker_id}`: fluent worker id
+
 ## License
 
 Apache License, Version 2.0

lib/fluent/plugin/filter_throttle.rb

@@ -5,6 +5,7 @@
 module Fluent::Plugin
   class ThrottleFilter < Filter
     Fluent::Plugin.register_filter('throttle', self)
+    include Fluent::Plugin::PrometheusLabelParser
     include Fluent::Plugin::Prometheus
 
     desc "Used to group logs. Groups are rate limited independently"
@@ -61,7 +62,7 @@ def configure(conf)
 
       @group_key_paths = group_key.map { |key| key.split(".") }
       @group_key_symbols = (group_key.map {|str| str.gsub(/[^a-zA-Z0-9_]/,'_')}).map(&:to_sym)
-      
+
       raise "group_bucket_period_s must be > 0" \
         unless @group_bucket_period_s > 0
 
@@ -83,7 +84,17 @@ def configure(conf)
       raise "group_warning_delay_s must be >= 1" \
         unless @group_warning_delay_s >= 1
 
-      @base_labels = {}
+      hostname = Socket.gethostname
+      expander_builder = Fluent::Plugin::Prometheus.placeholder_expander(log)
+      expander = expander_builder.build({ 'hostname' => hostname, 'worker_id' => fluentd_worker_id })
+      @base_labels = parse_labels_elements(conf)
+      @base_labels.each do |key, value|
+        unless value.is_a?(String)
+          raise Fluent::ConfigError, "record accessor syntax is not available in metric labels for throttle plugin"
+        end
+        @base_labels[key] = expander.expand(value)
+      end
+
     end
 
     def start