Hard-code non-configurable sampler intervals

While these samplers had intervals in 1_settings.rb, those weren't
exposed anywhere else: in the `gitlab.yml.example` file, in
`gitlab.rb.template` in Omnibus, or in our Helm charts.

Based on that, it doesn't appear that we expected people to configure
these intervals, so we should make the hard-coding explicit.

config/gitlab.yml.example

@@ -1078,8 +1078,6 @@ production: &base
   monitoring:
     # Time between sampling of unicorn socket metrics, in seconds
     # unicorn_sampler_interval: 10
-    # Time between sampling of Puma metrics, in seconds
-    # puma_sampler_interval: 5
     # IP whitelist to access monitoring endpoints
     ip_whitelist:
       - 127.0.0.0/8

config/initializers/1_settings.rb

@@ -728,9 +728,6 @@ Settings.action_cable['worker_pool_size'] ||= 4
 Settings['monitoring'] ||= Settingslogic.new({})
 Settings.monitoring['ip_whitelist'] ||= ['127.0.0.1/8']
 Settings.monitoring['unicorn_sampler_interval'] ||= 10
-Settings.monitoring['puma_sampler_interval'] ||= 5
-Settings.monitoring['ruby_sampler_interval'] ||= 60
-Settings.monitoring['global_search_sampler_interval'] ||= 60
 Settings.monitoring['sidekiq_exporter'] ||= Settingslogic.new({})
 Settings.monitoring.sidekiq_exporter['enabled'] ||= false
 Settings.monitoring.sidekiq_exporter['address'] ||= 'localhost'

config/initializers/7_prometheus_metrics.rb

@@ -42,11 +42,11 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
   Gitlab::Cluster::LifecycleEvents.on_worker_start do
     defined?(::Prometheus::Client.reinitialize_on_pid_change) && Prometheus::Client.reinitialize_on_pid_change
 
-    Gitlab::Metrics::Samplers::RubySampler.initialize_instance(Settings.monitoring.ruby_sampler_interval).start
-    Gitlab::Metrics::Samplers::DatabaseSampler.initialize_instance(Gitlab::Metrics::Samplers::DatabaseSampler::SAMPLING_INTERVAL_SECONDS).start
+    Gitlab::Metrics::Samplers::RubySampler.initialize_instance.start
+    Gitlab::Metrics::Samplers::DatabaseSampler.initialize_instance.start
 
     if Gitlab.ee? && Gitlab::Runtime.sidekiq?
-      Gitlab::Metrics::Samplers::GlobalSearchSampler.instance(Settings.monitoring.global_search_sampler_interval).start
+      Gitlab::Metrics::Samplers::GlobalSearchSampler.instance.start
     end
   rescue IOError => e
     Gitlab::ErrorTracking.track_exception(e)
@@ -59,7 +59,7 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     if Gitlab::Runtime.unicorn?
       Gitlab::Metrics::Samplers::UnicornSampler.instance(Settings.monitoring.unicorn_sampler_interval).start
     elsif Gitlab::Runtime.puma?
-      Gitlab::Metrics::Samplers::PumaSampler.instance(Settings.monitoring.puma_sampler_interval).start
+      Gitlab::Metrics::Samplers::PumaSampler.instance.start
     end
 
     Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION }, 1)

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

@@ -4,6 +4,8 @@ module Gitlab
   module Metrics
     module Samplers
       class GlobalSearchSampler < BaseSampler
+        SAMPLING_INTERVAL_SECONDS = 60
+
         def sample
           ::Elastic::MetricsUpdateService.new.execute
         end

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

@@ -3,7 +3,17 @@
 require 'spec_helper'
 
 describe Gitlab::Metrics::Samplers::GlobalSearchSampler do
-  subject { described_class.new(60.seconds) }
+  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
 
   describe '#sample' do
     it 'invokes the Elastic::MetricsUpdateService' do

lib/gitlab/metrics/samplers/base_sampler.rb

@@ -6,8 +6,10 @@ module Gitlab
   module Metrics
     module Samplers
       class BaseSampler < Daemon
+        attr_reader :interval
+
         # interval - The sampling interval in seconds.
-        def initialize(interval)
+        def initialize(interval = self.class::SAMPLING_INTERVAL_SECONDS)
           interval_half = interval.to_f / 2
 
           @interval = interval

lib/gitlab/metrics/samplers/puma_sampler.rb

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

lib/gitlab/metrics/samplers/ruby_sampler.rb

@@ -6,9 +6,10 @@ module Gitlab
   module Metrics
     module Samplers
       class RubySampler < BaseSampler
+        SAMPLING_INTERVAL_SECONDS = 60
         GC_REPORT_BUCKETS = [0.005, 0.01, 0.02, 0.04, 0.07, 0.1, 0.5].freeze
 
-        def initialize(interval)
+        def initialize(*)
           GC::Profiler.clear
 
           metrics[:process_start_time_seconds].set(labels, Time.now.to_i)

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

@@ -3,7 +3,17 @@
 require 'spec_helper'
 
 describe Gitlab::Metrics::Samplers::DatabaseSampler do
-  subject { described_class.new(described_class::SAMPLING_INTERVAL_SECONDS) }
+  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
 
   describe '#sample' do
     before do

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

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 describe Gitlab::Metrics::Samplers::PumaSampler do
-  subject { described_class.new(5) }
+  subject { described_class.new }
 
   let(:null_metric) { double('null_metric', set: nil, observe: nil) }
 
@@ -11,6 +11,16 @@ 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
+
   describe '#sample' do
     before do
       expect(subject).to receive(:puma_stats).and_return(puma_stats)

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

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 describe Gitlab::Metrics::Samplers::RubySampler do
-  let(:sampler) { described_class.new(5) }
+  let(:sampler) { described_class.new }
   let(:null_metric) { double('null_metric', set: nil, observe: nil) }
 
   before do
@@ -18,6 +18,16 @@ 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)