DataDog · marcotc · Jul 14, 2023 · Jul 14, 2023 · Jul 14, 2023 · Jul 14, 2023
@@ -2239,6 +2239,7 @@ For example, if `tracing.sampling.default_rate` is configured by [Remote Configu
 | `tracing.sampler`                                       |                                | `nil`                                                             | Advanced usage only. Sets a custom `Datadog::Tracing::Sampling::Sampler` instance. If provided, the tracer will use this sampler to determine sampling behavior. See [Application-side sampling](#application-side-sampling) for details. |
 | `tracing.sampling.default_rate`                         | `DD_TRACE_SAMPLE_RATE`         | `nil`                                                             | Sets the trace sampling rate between `0.0` (0%) and `1.0` (100%). See [Application-side sampling](#application-side-sampling) for details.                                                                                                  |
 | `tracing.sampling.rate_limit`                           | `DD_TRACE_RATE_LIMIT`          | `100` (per second)                                                | Sets a maximum number of traces per second to sample. Set a rate limit to avoid the ingestion volume overages in the case of traffic spikes.                                                                    |
+| `tracing.sampling.rules`                                | `DD_TRACE_SAMPLING_RULES`      | `nil`                                                             | Sets trace-level sampling rules, matching against the local root span. The format is a `String` with JSON, containing an Array of Objects. Each Object must have a float attribute `sample_rate` (between 0.0 and 1.0, inclusive), and optionally `name` and `service` string attributes. `name` and `service` control to which traces this sampling rule applies; if both are absent, then this rule applies to all traces. Rules are evaluted in order of declartion in the array; only the first to match is applied. If none apply, then `tracing.sampling.default_rate` is applied. |
 | `tracing.sampling.span_rules`                           | `DD_SPAN_SAMPLING_RULES`,`ENV_SPAN_SAMPLING_RULES_FILE` | `nil`                                    | Sets [Single Span Sampling](#single-span-sampling) rules. These rules allow you to keep spans even when their respective traces are dropped.                                                                                              |
 | `tracing.trace_id_128_bit_generation_enabled` | `DD_TRACE_128_BIT_TRACEID_GENERATION_ENABLED` | `false` | `true` to generate 128 bits trace ID and `false` to generate 64 bits trace ID  |
 | `tracing.report_hostname`                               | `DD_TRACE_REPORT_HOSTNAME`     | `false`                                                           | Adds hostname tag to traces.                                                                                                                                                                                                              |

@@ -62,6 +62,20 @@ def build_sampler(settings)
           else
             ensure_priority_sampling(sampler, settings)
           end
+        elsif (rules = settings.tracing.sampling.rules)
+          Tracing::Sampling::PrioritySampler.new(
+            base_sampler: Tracing::Sampling::AllSampler.new,
+            post_sampler: Tracing::Sampling::RuleSampler.parse(
+              rules,
+              settings.tracing.sampling.rate_limit,
+              settings.tracing.sampling.default_rate
+            ) ||
+              # Fallback RuleSampler in case `rules` parsing fails
+              Tracing::Sampling::RuleSampler.new(
+                rate_limit: settings.tracing.sampling.rate_limit,
+                default_sample_rate: settings.tracing.sampling.default_rate
+              )
+          )
         elsif settings.tracing.priority_sampling == false
           Tracing::Sampling::RuleSampler.new(
             rate_limit: settings.tracing.sampling.rate_limit,

@@ -72,6 +72,7 @@ module NET
         module Sampling
           ENV_SAMPLE_RATE = 'DD_TRACE_SAMPLE_RATE'
           ENV_RATE_LIMIT = 'DD_TRACE_RATE_LIMIT'
+          ENV_RULES = 'DD_TRACE_SAMPLING_RULES'
 
           # @public_api
           module Span

@@ -277,6 +277,22 @@ def self.extended(base)
                   o.default { env_to_float(Tracing::Configuration::Ext::Sampling::ENV_RATE_LIMIT, 100) }
                 end
 
+                # Trace sampling rules.
+                # These rules control whether a trace is kept or dropped by the tracer.
+                #
+                # The `rules` format is a String with a JSON array of objects:
+                # Each object must have a `sample_rate`, and the `name` and `service` fields
+                # are optional. The `sample_rate` value must be between 0.0 and 1.0 (inclusive).
+                # `name` and `service` are Strings that allow the `sample_rate` to be applied only
+                # to traces matching the `name` and `service`.
+                #
+                # @default `DD_TRACE_SAMPLING_RULES` environment variable. Otherwise `nil`.
+                # @return [String,nil]
+                # @public_api
+                option :rules do |o|
+                  o.default { ENV.fetch(Configuration::Ext::Sampling::ENV_RULES, nil) }
+                end
+
                 # Single span sampling rules.
                 # These rules allow a span to be kept when its encompassing trace is dropped.
                 #

@@ -48,6 +48,33 @@ def initialize(
                              end
         end
 
+        def self.parse(rules, rate_limit, default_sample_rate)
+          rules = JSON.parse(rules).map do |rule|
+            sample_rate = rule['sample_rate']
+
+            begin
+              sample_rate = Float(sample_rate)
+            rescue
+              raise "Rule '#{rule.inspect}' does not contain a float property `sample_rate`"
+            end
+
+            kwargs = {
+              name: rule['name'],
+              service: rule['service'],
+              sample_rate: sample_rate,
+            }.compact
+
+            SimpleRule.new(**kwargs)
+          end
+
+          new(rules, rate_limit: rate_limit, default_sample_rate: default_sample_rate)
+        rescue => e
+          Datadog.logger.error do
+            "Could not parse trace sampling rules '#{rules}': #{e.class.name} #{e.message} at #{Array(e.backtrace).first}"
+          end
+          nil
+        end
+
         # /RuleSampler's components (it's rate limiter, for example) are
         # not be guaranteed to be size-effect free.
         # It is not possible to guarantee that a call to {#sample?} will

@@ -44,6 +44,7 @@ module Datadog
           ENV_REPORT_HOSTNAME: "DD_TRACE_REPORT_HOSTNAME"
         end
         module Sampling
+          ENV_RULES: String
           ENV_SAMPLE_RATE: "DD_TRACE_SAMPLE_RATE"
 
           ENV_RATE_LIMIT: "DD_TRACE_RATE_LIMIT"

@@ -634,6 +634,26 @@
         end
       end
 
+      context 'with sampling.rules' do
+        before { allow(settings.tracing.sampling).to receive(:rules).and_return(rules) }
+
+        context 'with rules' do
+          let(:rules) { '[{"sample_rate":"0.123"}]' }
+
+          it_behaves_like 'new tracer' do
+            let(:sampler) do
+              lambda do |sampler|
+                expect(sampler).to be_a(Datadog::Tracing::Sampling::PrioritySampler)
+                expect(sampler.pre_sampler).to be_a(Datadog::Tracing::Sampling::AllSampler)
+
+                expect(sampler.priority_sampler.rules).to have(1).item
+                expect(sampler.priority_sampler.rules[0].sampler.sample_rate).to eq(0.123)
+              end
+            end
+          end
+        end
+      end
+
       context 'with sampling.span_rules' do
         before { allow(settings.tracing.sampling).to receive(:span_rules).and_return(rules) }
 

@@ -457,6 +457,24 @@ def propagation_inject_style
         end
       end
 
+      describe '#rules' do
+        subject(:rules) { settings.tracing.sampling.rules }
+
+        context 'default' do
+          it { is_expected.to be_nil }
+        end
+
+        context 'when ENV is provided' do
+          around do |example|
+            ClimateControl.modify('DD_TRACE_SAMPLING_RULES' => '[{"sample_rate":0.2}]') do
+              example.run
+            end
+          end
+
+          it { is_expected.to eq('[{"sample_rate":0.2}]') }
+        end
+      end
+
       describe '#span_rules' do
         subject(:rules) { settings.tracing.sampling.span_rules }
 

@@ -285,6 +285,17 @@ def agent_receives_span_step3(previous_success)
       it_behaves_like 'sampling decision', nil
     end
 
+    shared_context 'DD_TRACE_SAMPLING_RULES configuration' do
+      let(:sampler) { nil }
+      let(:rules_json) { [rule].to_json }
+
+      around do |example|
+        ClimateControl.modify('DD_TRACE_SAMPLING_RULES' => rules_json) do
+          example.run
+        end
+      end
+    end
+
     context 'with rule' do
       let(:rule_sampler) { Datadog::Tracing::Sampling::RuleSampler.new([rule], **rule_sampler_opt) }
       let(:rule_sampler_opt) { {} }
@@ -298,6 +309,18 @@ def agent_receives_span_step3(previous_success)
         it_behaves_like 'rate limit metric', 1.0
         it_behaves_like 'sampling decision', '-3'
 
+        context 'set through DD_TRACE_SAMPLING_RULES environment variable' do
+          include_context 'DD_TRACE_SAMPLING_RULES configuration' do
+            let(:rule) { { name: 'my.op', sample_rate: 1.0 } }
+          end
+
+          it_behaves_like 'flushed trace'
+          it_behaves_like 'priority sampled', Datadog::Tracing::Sampling::Ext::Priority::USER_KEEP
+          it_behaves_like 'rule sampling rate metric', 1.0
+          it_behaves_like 'rate limit metric', 1.0
+          it_behaves_like 'sampling decision', '-3'
+        end
+
         context 'with low sample rate' do
           let(:rule) { Datadog::Tracing::Sampling::SimpleRule.new(sample_rate: Float::MIN) }
 
@@ -306,6 +329,18 @@ def agent_receives_span_step3(previous_success)
           it_behaves_like 'rule sampling rate metric', Float::MIN
           it_behaves_like 'rate limit metric', nil # Rate limiter is never reached, thus has no value to provide
           it_behaves_like 'sampling decision', nil
+
+          context 'set through DD_TRACE_SAMPLING_RULES environment variable' do
+            include_context 'DD_TRACE_SAMPLING_RULES configuration' do
+              let(:rule) { { sample_rate: Float::MIN } }
+            end
+
+            it_behaves_like 'flushed trace'
+            it_behaves_like 'priority sampled', Datadog::Tracing::Sampling::Ext::Priority::USER_REJECT
+            it_behaves_like 'rule sampling rate metric', Float::MIN
+            it_behaves_like 'rate limit metric', nil # Rate limiter is never reached, thus has no value to provide
+            it_behaves_like 'sampling decision', nil
+          end
         end
 
         context 'rate limited' do
@@ -328,6 +363,19 @@ def agent_receives_span_step3(previous_success)
         it_behaves_like 'rule sampling rate metric', nil
         it_behaves_like 'rate limit metric', nil
         it_behaves_like 'sampling decision', '-0'
+
+        context 'set through DD_TRACE_SAMPLING_RULES environment variable' do
+          include_context 'DD_TRACE_SAMPLING_RULES configuration' do
+            let(:rule) { { name: 'not.my.op' } }
+
+            it_behaves_like 'flushed trace'
+            # The PrioritySampler was responsible for the sampling decision, not the Rule Sampler.
+            it_behaves_like 'priority sampled', Datadog::Tracing::Sampling::Ext::Priority::AUTO_KEEP
+            it_behaves_like 'rule sampling rate metric', nil
+            it_behaves_like 'rate limit metric', nil
+            it_behaves_like 'sampling decision', '-0'
+          end
+        end
       end
     end
   end

@@ -77,6 +77,100 @@
     end
   end
 
+  describe 'parse' do
+    subject(:parse) { described_class.parse(rules.to_json, rate_limit, default_sample_rate) }
+    let(:rules) { [rule] }
+    let(:rate_limit) { nil }
+    let(:default_sample_rate) { nil }
+
+    let(:actual_rule) do
+      subject
+      expect(parse.rules).to have(1).item
+      parse.rules[0]
+    end
+
+    let(:actual_rules) do
+      subject
+      parse.rules
+    end
+
+    context 'with sample_rate' do
+      let(:rule) { { sample_rate: 0.1 } }
+
+      it 'parses as a match any' do
+        expect(actual_rule.matcher.name).to eq(Datadog::Tracing::Sampling::SimpleMatcher::MATCH_ALL)
+        expect(actual_rule.matcher.service).to eq(Datadog::Tracing::Sampling::SimpleMatcher::MATCH_ALL)
+        expect(actual_rule.sampler.sample_rate).to eq(0.1)
+      end
+
+      context 'and name' do
+        let(:rule) { super().merge(name: 'test-name') }
+
+        it 'parses matching any service' do
+          expect(actual_rule.matcher.name).to eq('test-name')
+          expect(actual_rule.matcher.service).to eq(Datadog::Tracing::Sampling::SimpleMatcher::MATCH_ALL)
+          expect(actual_rule.sampler.sample_rate).to eq(0.1)
+        end
+      end
+
+      context 'and service' do
+        let(:rule) { super().merge(service: 'test-service') }
+
+        it 'parses matching any name' do
+          expect(actual_rule.matcher.name).to eq(Datadog::Tracing::Sampling::SimpleMatcher::MATCH_ALL)
+          expect(actual_rule.matcher.service).to eq('test-service')
+          expect(actual_rule.sampler.sample_rate).to eq(0.1)
+        end
+      end
+
+      context 'with multiple rules' do
+        let(:rules) { [{ sample_rate: 0.1 }, { sample_rate: 0.2 }] }
+
+        it 'parses all rules in order' do
+          expect(actual_rules).to have(2).item
+          expect(actual_rules[0].sampler.sample_rate).to eq(0.1)
+          expect(actual_rules[1].sampler.sample_rate).to eq(0.2)
+        end
+      end
+    end
+
+    context 'with a non-float sample_rate' do
+      let(:rule) { { sample_rate: 'oops' } }
+
+      it 'does not accept rule with a non-float sample_rate' do
+        expect(Datadog.logger).to receive(:error)
+        is_expected.to be_nil
+      end
+    end
+
+    context 'without a sample_rate' do
+      let(:rule) { { name: 'test' } }
+
+      it 'does not accept rule missing the mandatory sample_rate' do
+        expect(Datadog.logger).to receive(:error)
+        is_expected.to be_nil
+      end
+
+      context 'with multiple rules' do
+        let(:rules) { [{ sample_rate: 0.1 }, { name: 'test' }] }
+
+        it 'rejects all rules if one is missing the mandatory sample_rate' do
+          expect(Datadog.logger).to receive(:error)
+          is_expected.to be_nil
+        end
+      end
+    end
+
+    context 'without a valid JSON array' do
+      let(:rules) { 'not a json array' }
+
+      it 'returns nil in case of parsing error' do
+        expect(Datadog.logger).to receive(:error)
+        is_expected.to be_nil
+      end
+    end
+  end
+
   shared_context 'matching rule' do
     let(:rules) { [rule] }
     let(:rule) { instance_double(Datadog::Tracing::Sampling::Rule) }