fix(platform): PAYMENTS-11567 Require time stdlib, clamp negative queue latency, fix changelog

Author: Willem Homan

CHANGELOG.md

@@ -2,7 +2,7 @@ Changelog for the bc-prometheus-ruby gem.
 
 ### Pending Release
 
-- Add opt-in per-Resque-job histograms `resque_job_queue_latency_seconds` and `resque_job_perform_duration_seconds`, labelled by `job_class`. Recorded from the parent worker process (via `Resque.before_fork` and a `Module#prepend` around `Resque::Worker#perform_with_fork`), so no synchronous flush is needed in the forked child. Gated by `PROMETHEUS_RESQUE_PER_JOB_METRICS_ENABLED` (default off).
+- Add opt-in per-Resque-job histograms `resque_job_queue_latency_seconds` and `resque_job_perform_duration_seconds`, labelled by `job_class`. Recorded from the parent worker process via a `Module#prepend` around `Resque::Worker#perform_with_fork` (queue latency before the fork, perform duration after), so no synchronous flush is needed in the forked child. Gated by `PROMETHEUS_RESQUE_PER_JOB_METRICS_ENABLED` (default off).
 
 ## 0.8.1
 

lib/bigcommerce/prometheus/integrations/resque/job_metrics.rb

@@ -83,10 +83,15 @@ def record_queue_latency(payload)
               anchor = payload.anchor_time
               return unless anchor
 
+              # Clock skew between the enqueuer/scheduler and the worker can put
+              # the anchor in the future; clamp so the histogram never records a
+              # negative latency.
+              latency = (Time.now - anchor).to_f.clamp(0.0..)
+
               @client.send_json(
                 type: 'resque_job',
                 metric: 'queue_latency',
-                value: (Time.now - anchor).to_f,
+                value: latency,
                 custom_labels: { job_class: payload.job_class }
               )
             rescue StandardError => e

lib/bigcommerce/prometheus/integrations/resque/job_payload.rb

@@ -15,6 +15,8 @@
 # COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 # OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #
+require 'time'
+
 module Bigcommerce
   module Prometheus
     module Integrations

spec/bigcommerce/prometheus/integrations/resque/job_metrics_spec.rb

@@ -91,8 +91,18 @@ def active_job_payload(job_class: 'MyJob', enqueued_at: nil, scheduled_at: nil)
       described_class.record_queue_latency(payload_for(active_job_payload(enqueued_at: enqueued)))
     end
 
+    it 'clamps the value to zero when the anchor is in the future (clock skew)' do
+      future = (Time.now + 5).iso8601(6)
+
+      expect(client).to receive(:send_json).with(
+        hash_including(metric: 'queue_latency', value: 0.0)
+      )
+
+      described_class.record_queue_latency(payload_for(active_job_payload(enqueued_at: future)))
+    end
+
     it 'is a no-op for a vanilla Resque payload (no anchor available, no exception)' do
-      payload = { 'class' => 'RawResqueJob', 'args' => [12345, 'some_string'] }
+      payload = { 'class' => 'RawResqueJob', 'args' => [12_345, 'some_string'] }
 
       expect(client).not_to receive(:send_json)
 
@@ -128,7 +138,7 @@ def active_job_payload(job_class: 'MyJob', enqueued_at: nil, scheduled_at: nil)
     end
 
     it 'labels with the raw Resque payload class for vanilla Resque jobs' do
-      payload = { 'class' => 'RawResqueJob', 'args' => [12345, 'some_string'] }
+      payload = { 'class' => 'RawResqueJob', 'args' => [12_345, 'some_string'] }
 
       expect(client).to receive(:send_json).with(
         hash_including(custom_labels: { job_class: 'RawResqueJob' })