Allow sampler intervals to be configured via env

This is useful for development but also to more easily
change these values in production.

changelogs/unreleased/mk-configurable-sampling-intervals.yml

+---
+title: Sampler intervals can now be configured via env vars
+merge_request: 50625
+author:
+type: other

doc/administration/monitoring/performance/index.md

@@ -61,3 +61,14 @@ half above the interval. For example, for a user defined interval of 15 seconds
 the actual interval can be anywhere between 7.5 and 22.5. The interval is
 re-generated for every sampling run instead of being generated one time and reused
 for the duration of the process' lifetime.
+
+User defined intervals can be specified by means of environment variables.
+The following environment variables are recognized:
+
+- `RUBY_SAMPLER_INTERVAL_SECONDS`
+- `DATABASE_SAMPLER_INTERVAL_SECONDS`
+- `ACTION_CABLE_SAMPLER_INTERVAL_SECONDS`
+- `PUMA_SAMPLER_INTERVAL_SECONDS`
+- `UNICORN_SAMPLER_INTERVAL_SECONDS`
+- `THREADS_SAMPLER_INTERVAL_SECONDS`
+- `GLOBAL_SEARCH_SAMPLER_INTERVAL_SECONDS`

ee/lib/gitlab/metrics/samplers/global_search_sampler.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     module Samplers
       class GlobalSearchSampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 60
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 60
 
         def sample
           ::Elastic::MetricsUpdateService.new.execute

ee/spec/lib/ee/gitlab/metrics/samplers/database_sampler_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Metrics::Samplers::DatabaseSampler do
-  subject { described_class.new(described_class::SAMPLING_INTERVAL_SECONDS) }
+  subject { described_class.new }
 
   describe '#sample' do
     before do

ee/spec/lib/gitlab/metrics/samplers/global_search_sampler_spec.rb

@@ -5,15 +5,7 @@ require 'spec_helper'
 RSpec.describe Gitlab::Metrics::Samplers::GlobalSearchSampler do
   subject { described_class.new }
 
-  describe '#interval' do
-    it 'samples every sixty seconds by default' do
-      expect(subject.interval).to eq(60)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
+  it_behaves_like 'metrics sampler', 'GLOBAL_SEARCH_SAMPLER'
 
   describe '#sample' do
     it 'invokes the Elastic::MetricsUpdateService' do

lib/gitlab/metrics/samplers/action_cable_sampler.rb

@@ -4,9 +4,9 @@ module Gitlab
   module Metrics
     module Samplers
       class ActionCableSampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 5
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 5
 
-        def initialize(interval = SAMPLING_INTERVAL_SECONDS, action_cable: ::ActionCable.server)
+        def initialize(interval = nil, action_cable: ::ActionCable.server)
           super(interval)
           @action_cable = action_cable
         end

lib/gitlab/metrics/samplers/base_sampler.rb

@@ -9,7 +9,9 @@ module Gitlab
         attr_reader :interval
 
         # interval - The sampling interval in seconds.
-        def initialize(interval = self.class::SAMPLING_INTERVAL_SECONDS)
+        def initialize(interval = nil)
+          interval ||= ENV[interval_env_key]&.to_i
+          interval ||= self.class::DEFAULT_SAMPLING_INTERVAL_SECONDS
           interval_half = interval.to_f / 2
 
           @interval = interval
@@ -50,6 +52,14 @@ module Gitlab
 
         attr_reader :running
 
+        def sampler_class
+          self.class.name.demodulize
+        end
+
+        def interval_env_key
+          "#{sampler_class.underscore.upcase}_INTERVAL_SECONDS"
+        end
+
         def start_working
           @running = true
 

lib/gitlab/metrics/samplers/database_sampler.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     module Samplers
       class DatabaseSampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 5
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 5
 
         METRIC_PREFIX = 'gitlab_database_connection_pool_'
 

lib/gitlab/metrics/samplers/puma_sampler.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     module Samplers
       class PumaSampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 5
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 5
 
         def metrics
           @metrics ||= init_metrics

lib/gitlab/metrics/samplers/ruby_sampler.rb

@@ -6,7 +6,7 @@ module Gitlab
   module Metrics
     module Samplers
       class RubySampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 60
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 60
         GC_REPORT_BUCKETS = [0.005, 0.01, 0.02, 0.04, 0.07, 0.1, 0.5].freeze
 
         def initialize(*)

lib/gitlab/metrics/samplers/threads_sampler.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     module Samplers
       class ThreadsSampler < BaseSampler
-        SAMPLING_INTERVAL_SECONDS = 5
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 5
         KNOWN_PUMA_THREAD_NAMES = ['puma worker check pipe', 'puma server',
                                    'puma threadpool reaper', 'puma threadpool trimmer',
                                    'puma worker check pipe', 'puma stat payload'].freeze

lib/gitlab/metrics/samplers/unicorn_sampler.rb

@@ -4,6 +4,8 @@ module Gitlab
   module Metrics
     module Samplers
       class UnicornSampler < BaseSampler
+        DEFAULT_SAMPLING_INTERVAL_SECONDS = 5
+
         def metrics
           @metrics ||= init_metrics
         end

spec/lib/gitlab/metrics/samplers/action_cable_sampler_spec.rb

@@ -7,15 +7,7 @@ RSpec.describe Gitlab::Metrics::Samplers::ActionCableSampler do
 
   subject { described_class.new(action_cable: action_cable) }
 
-  describe '#interval' do
-    it 'samples every five seconds by default' do
-      expect(subject.interval).to eq(5)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
+  it_behaves_like 'metrics sampler', 'ACTION_CABLE_SAMPLER'
 
   describe '#sample' do
     let(:pool) { instance_double(Concurrent::ThreadPoolExecutor) }

spec/lib/gitlab/metrics/samplers/database_sampler_spec.rb

@@ -5,15 +5,7 @@ require 'spec_helper'
 RSpec.describe Gitlab::Metrics::Samplers::DatabaseSampler do
   subject { described_class.new }
 
-  describe '#interval' do
-    it 'samples every five seconds by default' do
-      expect(subject.interval).to eq(5)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
+  it_behaves_like 'metrics sampler', 'DATABASE_SAMPLER'
 
   describe '#sample' do
     before do

spec/lib/gitlab/metrics/samplers/puma_sampler_spec.rb

@@ -11,15 +11,7 @@ RSpec.describe Gitlab::Metrics::Samplers::PumaSampler do
     allow(Gitlab::Metrics::NullMetric).to receive(:instance).and_return(null_metric)
   end
 
-  describe '#interval' do
-    it 'samples every five seconds by default' do
-      expect(subject.interval).to eq(5)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
+  it_behaves_like 'metrics sampler', 'PUMA_SAMPLER'
 
   describe '#sample' do
     before do

spec/lib/gitlab/metrics/samplers/ruby_sampler_spec.rb

@@ -10,6 +10,8 @@ RSpec.describe Gitlab::Metrics::Samplers::RubySampler do
     allow(Gitlab::Metrics::NullMetric).to receive(:instance).and_return(null_metric)
   end
 
+  it_behaves_like 'metrics sampler', 'RUBY_SAMPLER'
+
   describe '#initialize' do
     it 'sets process_start_time_seconds' do
       freeze_time do
@@ -18,16 +20,6 @@ RSpec.describe Gitlab::Metrics::Samplers::RubySampler do
     end
   end
 
-  describe '#interval' do
-    it 'samples every sixty seconds by default' do
-      expect(subject.interval).to eq(60)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
-
   describe '#sample' do
     it 'adds a metric containing the process resident memory bytes' do
       expect(Gitlab::Metrics::System).to receive(:memory_usage_rss).and_return(9000)

spec/lib/gitlab/metrics/samplers/threads_sampler_spec.rb

@@ -5,15 +5,7 @@ require 'spec_helper'
 RSpec.describe Gitlab::Metrics::Samplers::ThreadsSampler do
   subject { described_class.new }
 
-  describe '#interval' do
-    it 'samples every five seconds by default' do
-      expect(subject.interval).to eq(5)
-    end
-
-    it 'samples at other intervals if requested' do
-      expect(described_class.new(11).interval).to eq(11)
-    end
-  end
+  it_behaves_like 'metrics sampler', 'THREADS_SAMPLER'
 
   describe '#sample' do
     before do

spec/lib/gitlab/metrics/samplers/unicorn_sampler_spec.rb

@@ -5,6 +5,8 @@ require 'spec_helper'
 RSpec.describe Gitlab::Metrics::Samplers::UnicornSampler do
   subject { described_class.new(1.second) }
 
+  it_behaves_like 'metrics sampler', 'UNICORN_SAMPLER'
+
   describe '#sample' do
     let(:unicorn) { Module.new }
     let(:raindrops) { double('raindrops') }

spec/support/shared_examples/metrics/sampler_shared_examples.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples 'metrics sampler' do |env_prefix|
+  context 'when sampling interval is passed explicitly' do
+    subject { described_class.new(42) }
+
+    specify { expect(subject.interval).to eq(42) }
+  end
+
+  context 'when sampling interval is passed through the environment' do
+    subject { described_class.new }
+
+    before do
+      stub_env("#{env_prefix}_INTERVAL_SECONDS", '42')
+    end
+
+    specify { expect(subject.interval).to eq(42) }
+  end
+
+  context 'when no sampling interval is passed anywhere' do
+    subject { described_class.new }
+
+    it 'uses the hardcoded default' do
+      expect(subject.interval).to eq(described_class::DEFAULT_SAMPLING_INTERVAL_SECONDS)
+    end
+  end
+end