Create Prometheus Exporter

Gemfile

@@ -10,6 +10,7 @@ gem 'lograge'
 gem 'logstash-event'
 gem 'pg', '>= 0.18', '< 2.0'
 gem 'puma', '~> 3.11'
+gem 'prometheus_exporter'
 gem 'rails', '~> 5.2.2'
 gem 'sentry-raven'
 

Gemfile.lock

@@ -98,6 +98,7 @@ GEM
       ast (~> 2.4.0)
     pg (1.1.4)
     powerpack (0.1.2)
+    prometheus_exporter (0.4.2)
     puma (3.12.0)
     rack (2.0.6)
     rack-test (1.1.0)
@@ -203,6 +204,7 @@ DEPENDENCIES
   lograge
   logstash-event
   pg (>= 0.18, < 2.0)
+  prometheus_exporter
   puma (~> 3.11)
   rails (~> 5.2.2)
   rspec-rails

config/initializers/metrics.rb

@@ -0,0 +1,7 @@
+unless Rails.env.test?
+  require 'prometheus_exporter/instrumentation'
+  require 'prometheus_exporter/middleware'
+
+  PrometheusExporter::Instrumentation::Process.start(type: 'master')
+  Rails.application.middleware.unshift PrometheusExporter::Middleware
+end

config/puma_prod.rb

@@ -14,3 +14,13 @@
   # See: https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server#on-worker-boot
   ActiveRecord::Base.establish_connection
 end
+
+after_worker_boot do
+  require 'prometheus_exporter/instrumentation'
+  PrometheusExporter::Instrumentation::Puma.start
+end
+
+after_fork do
+  require 'prometheus_exporter/instrumentation'
+  PrometheusExporter::Instrumentation::Process.start(type: 'web')
+end

deploy/deployment.yaml

@@ -89,3 +89,21 @@ spec:
                 secretKeyRef:
                   name: allocation-api-secrets
                   key: nomis_oauth_pub_key
+        - name: allocation-api-metrics
+          image: 926803513772.dkr.ecr.eu-west-1.amazonaws.com/offender-management/offender-management-allocation-api:latest
+          imagePullPolicy: Always
+          command: ['sh', '-c', "bundle exec puma prometheus_exporter --pidfile /tmp/server.pid"]
+          ports:
+            - containerPort: 9394
+          livenessProbe:
+            httpGet:
+              path: /metrics
+              port: 9394
+            initialDelaySeconds: 10
+            periodSeconds: 60
+          readinessProbe:
+            httpGet:
+              path: /metrics
+              port: 9394
+            initialDelaySeconds: 10
+            periodSeconds: 60

deploy/service-monitor.yaml

@@ -0,0 +1,15 @@
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: allocation-api
+  namespace: offender-management-staging
+spec:
+  selector:
+    matchLabels:
+      app: allocation-api
+  namespaceSelector:
+    matchNames:
+    - offender-management-staging
+  endpoints:
+  - port: "9394"
+    interval: 15s