Write to InfluxDB directly via UDP

This removes the need for Sidekiq and any overhead/problems introduced
by TCP. There are a few things to take into account:

1. When writing data to InfluxDB you may still get an error if the
   server becomes unavailable during the write. Because of this we're
   catching all exceptions and just ignore them (for now).
2. Writing via UDP apparently requires the timestamp to be in
   nanoseconds. Without this data either isn't written properly.
3. Due to the restrictions on UDP buffer sizes we're writing metrics one
   by one, instead of writing all of them at once.

4 files changed, 50 insertions, 10 deletions

diff --git a/spec/lib/gitlab/metrics/sampler_spec.rb b/spec/lib/gitlab/metrics/sampler_spec.rb
index 69376c0b79b..51a941c48cd 100644
--- a/spec/lib/gitlab/metrics/sampler_spec.rb
+++ b/spec/lib/gitlab/metrics/sampler_spec.rb
@@ -38,7 +38,7 @@ describe Gitlab::Metrics::Sampler do
 
   describe '#flush' do
     it 'schedules the metrics using Sidekiq' do
-      expect(MetricsWorker).to receive(:perform_async).
+      expect(Gitlab::Metrics).to receive(:submit_metrics).
         with([an_instance_of(Hash)])
 
       sampler.sample_memory_usage
diff --git a/spec/lib/gitlab/metrics/sidekiq_middleware_spec.rb b/spec/lib/gitlab/metrics/sidekiq_middleware_spec.rb
index 05214efc565..5882e7d81c7 100644
--- a/spec/lib/gitlab/metrics/sidekiq_middleware_spec.rb
+++ b/spec/lib/gitlab/metrics/sidekiq_middleware_spec.rb
@@ -11,14 +11,6 @@ describe Gitlab::Metrics::SidekiqMiddleware do
 
       middleware.call(worker, 'test', :test) { nil }
     end
-
-    it 'does not track jobs of the MetricsWorker' do
-      worker = MetricsWorker.new
-
-      expect(Gitlab::Metrics::Transaction).to_not receive(:new)
-
-      middleware.call(worker, 'test', :test) { nil }
-    end
   end
 
   describe '#tag_worker' do
diff --git a/spec/lib/gitlab/metrics/transaction_spec.rb b/spec/lib/gitlab/metrics/transaction_spec.rb
index 5f17ff8ee75..6862fc9e2d1 100644
--- a/spec/lib/gitlab/metrics/transaction_spec.rb
+++ b/spec/lib/gitlab/metrics/transaction_spec.rb
@@ -68,7 +68,7 @@ describe Gitlab::Metrics::Transaction do
     it 'submits the metrics to Sidekiq' do
       transaction.track_self
 
-      expect(MetricsWorker).to receive(:perform_async).
+      expect(Gitlab::Metrics).to receive(:submit_metrics).
         with([an_instance_of(Hash)])
 
       transaction.submit
diff --git a/spec/lib/gitlab/metrics_spec.rb b/spec/lib/gitlab/metrics_spec.rb
index 944642909aa..6c0682cac4d 100644
--- a/spec/lib/gitlab/metrics_spec.rb
+++ b/spec/lib/gitlab/metrics_spec.rb
@@ -33,4 +33,52 @@ describe Gitlab::Metrics do
       expect(file).to eq('spec/lib/gitlab/metrics_spec.rb')
     end
   end
+
+  describe '#submit_metrics' do
+    it 'prepares and writes the metrics to InfluxDB' do
+      connection = double(:connection)
+      pool       = double(:pool)
+
+      expect(pool).to receive(:with).and_yield(connection)
+      expect(connection).to receive(:write_points).with(an_instance_of(Array))
+      expect(Gitlab::Metrics).to receive(:pool).and_return(pool)
+
+      described_class.submit_metrics([{ 'series' => 'kittens', 'tags' => {} }])
+    end
+  end
+
+  describe '#prepare_metrics' do
+    it 'returns a Hash with the keys as Symbols' do
+      metrics = described_class.
+        prepare_metrics([{ 'values' => {}, 'tags' => {} }])
+
+      expect(metrics).to eq([{ values: {}, tags: {} }])
+    end
+
+    it 'escapes tag values' do
+      metrics = described_class.prepare_metrics([
+        { 'values' => {}, 'tags' => { 'foo' => 'bar=' } }
+      ])
+
+      expect(metrics).to eq([{ values: {}, tags: { 'foo' => 'bar\\=' } }])
+    end
+
+    it 'drops empty tags' do
+      metrics = described_class.prepare_metrics([
+        { 'values' => {}, 'tags' => { 'cats' => '', 'dogs' => nil } }
+      ])
+
+      expect(metrics).to eq([{ values: {}, tags: {} }])
+    end
+  end
+
+  describe '#escape_value' do
+    it 'escapes an equals sign' do
+      expect(described_class.escape_value('foo=')).to eq('foo\\=')
+    end
+
+    it 'casts values to Strings' do
+      expect(described_class.escape_value(10)).to eq('10')
+    end
+  end
 end