feat(fluentd): allow fluentd_thread label to be configurable (#6240)

Signed-off-by: Trevor Wood <Trevor.G.Wood@gmail.com>

CHANGELOG.md

@@ -312,6 +312,7 @@ to include only the most relevant.
 * [5223](https://github.com/grafana/loki/pull/5223) **cyriltovena**: fluent-bit: Attempt to unmarshal nested json.
 
 #### FluentD
+* [6240](https://github.com/grafana/loki/pull/6240) **taharah**: Add the feature flag `include_thread_label` to allow the `fluentd_thread` label included when using multiple threads for flushing to be configurable
 * [5107](https://github.com/grafana/loki/pull/5107) **chaudum**: fluentd: Fix bug that caused lines to be dropped when containing non utf-8 characters
 * [5163](https://github.com/grafana/loki/pull/5163) **chaudum**: Fix encoding error in fluentd client
 

clients/cmd/fluentd/lib/fluent/plugin/out_loki.rb

@@ -73,6 +73,9 @@ class LogPostError < StandardError; end
       desc 'if a record only has 1 key, then just set the log line to the value and discard the key.'
       config_param :drop_single_key, :bool, default: false
 
+      desc 'whether or not to include the fluentd_thread label when multiple threads are used for flushing'
+      config_param :include_thread_label, :bool, default: true
+
       config_section :buffer do
         config_set_default :@type, DEFAULT_BUFFER_TYPE
         config_set_default :chunk_keys, []
@@ -332,7 +335,7 @@ def line_to_loki(record)
         # unique per flush thread
         # note that flush thread != fluentd worker. if you use multiple workers you still need to
         # add the worker id as a label
-        if @buffer_config.flush_thread_count > 1
+        if @include_thread_label && @buffer_config.flush_thread_count > 1
           chunk_labels['fluentd_thread'] = Thread.current[:_fluentd_plugin_helper_thread_title].to_s
         end
 

clients/cmd/fluentd/spec/gems/fluent/plugin/loki_output_spec.rb

@@ -123,7 +123,7 @@
     expect(payload[0]['stream'].empty?).to eq true
     expect(payload[0]['values'].count).to eq 1
     expect(payload[0]['values'][0][0]).to eq "1546270458000000000"
-    expect(payload[0]['values'][0][1]).to eq "message=\"� rest of line\" number=1.2345 stream=stdout"
+    expect(payload[0]['values'][0][1]).to eq "message=\"? rest of line\" number=1.2345 stream=stdout"
   end
 
   it 'handle non utf-8 characters from log lines in json format' do
@@ -312,4 +312,52 @@
     allow(server_error).to receive(:body).and_return('fake body')
     expect { driver.instance.write(lines) }.to raise_error(described_class::LogPostError)
   end
+
+  context 'when output is multi-thread' do
+    let(:thread) do
+      class_double(
+        'Thread',
+        current: { _fluentd_plugin_helper_thread_title: 'thread1' }
+      ).as_stubbed_const
+    end
+
+    before do
+      allow(Thread).to receive(:new).and_yield(thread)
+    end
+
+    it 'adds the fluentd_label by default' do
+      config = <<-CONF
+        url https://logs-us-west1.grafana.net
+
+        <buffer>
+          @type memory
+          flush_thread_count 2
+        </buffer>
+      CONF
+      driver = Fluent::Test::Driver::Output.new(described_class)
+      driver.configure(config)
+      content = File.readlines('spec/gems/fluent/plugin/data/syslog2')
+      chunk = [Time.at(1_546_270_458), content[0]]
+      payload = driver.instance.generic_to_loki([chunk])
+      expect(payload[0]['stream']).to eq('fluentd_thread' => 'thread1')
+    end
+
+    it 'does not add the fluentd_label when configured' do
+      config = <<-CONF
+        url https://logs-us-west1.grafana.net
+        include_thread_label  false
+
+        <buffer>
+          @type memory
+          flush_thread_count 2
+        </buffer>
+      CONF
+      driver = Fluent::Test::Driver::Output.new(described_class)
+      driver.configure(config)
+      content = File.readlines('spec/gems/fluent/plugin/data/syslog2')
+      chunk = [Time.at(1_546_270_458), content[0]]
+      payload = driver.instance.generic_to_loki([chunk])
+      expect(payload[0]['stream'].empty?).to eq(true)
+    end
+  end
 end

docs/sources/clients/fluentd/_index.md

@@ -257,6 +257,7 @@ There are few configurations settings to control the output format.
 - remove_keys: (default: nil) comma separated list of needless record keys to remove. All other keys will be placed into the log line. You can use [record_accessor syntax](https://docs.fluentd.org/plugin-helper-overview/api-plugin-helper-record_accessor#syntax).
 - line_format (default:key_value): format to use when flattening the record to a log line. Valid values are "json" or "key_value". If set to "json" the log line sent to Loki will be the fluentd record (excluding any keys extracted out as labels) dumped as json. If set to "key_value", the log line will be each item in the record concatenated together (separated by a single space) in the format `<key>=<value>`.
 - drop_single_key: if set to true and a record only has 1 key after extracting `<label></label>` blocks, set the log line to the value and discard the key.
+- include_thread_label (default: true): whether or not to include the fluentd_thread label when multiple threads are used for flushing.
 
 ### Buffer options