Update prometheus-client. Use my fork with the :most_recent aggregation.

Gemfile

@@ -11,7 +11,7 @@ gem "addressable"
 gem "rack-ssl-enforcer"
 gem "clogger"
 gem "encrypted_strings"
-gem "prometheus-client", require: "prometheus/middleware/exporter"
+gem "prometheus-client", require: "prometheus/middleware/exporter", git: "https://github.com/stefansundin/prometheus-client.git", branch: "add-most_recent-aggregation"
 
 group :production do
   gem "airbrake", require: false

Gemfile.lock

@@ -1,3 +1,10 @@
+GIT
+  remote: https://github.com/stefansundin/prometheus-client.git
+  revision: 5256cdfb78d5bfec1b8fbb78dcc1a2eee6c8989f
+  branch: add-most_recent-aggregation
+  specs:
+    prometheus-client (1.0.0)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -30,8 +37,6 @@ GEM
     nio4r (2.5.2)
     powder (0.4.0)
       thor (>= 0.11.5)
-    prometheus-client (0.9.0)
-      quantile (~> 0.2.1)
     pry (0.12.2)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
@@ -41,7 +46,6 @@ GEM
     public_suffix (4.0.1)
     puma (4.3.1)
       nio4r (~> 2.0)
-    quantile (0.2.1)
     rack (2.0.8)
     rack-protection (2.0.7)
       rack
@@ -78,7 +82,7 @@ DEPENDENCIES
   github-release-party
   newrelic_rpm
   powder
-  prometheus-client
+  prometheus-client!
   pry-remote
   puma
   rack

app/github.rb

@@ -164,7 +164,7 @@ def self.graphql(query, variables, token=nil)
       }.to_json, headers)
       response = HTTPResponse.new(raw_response, uri.to_s)
       if response.json && response.json["data"] && response.json["data"]["rateLimit"] && response.json["data"]["rateLimit"]["remaining"]
-        $metrics[:ratelimit_remaining].set({}, response.json["data"]["rateLimit"]["remaining"])
+        $metrics[:ratelimit_remaining].set(response.json["data"]["rateLimit"]["remaining"])
       end
       return response
     end

config/initializers/40-prometheus.rb

@@ -1,7 +1,21 @@
-# The app is currently run with multiple processes, which means that the /metrics endpoint is not consistent.. That's fine for now, at least with this one metric.
+# frozen_string_literal: true
+
+# Use DirectFileStore if we run multiple processes
+store_settings = {}
+if ENV["WEB_CONCURRENCY"]
+  require "prometheus/client/data_stores/direct_file_store"
+  app_path = File.expand_path("../../..", __FILE__)
+  Prometheus::Client.config.data_store = Prometheus::Client::DataStores::DirectFileStore.new(dir: "#{app_path}/tmp/prometheus/")
+  store_settings[:aggregation] = :most_recent
+
+  # Clean up old metric files
+  Dir["#{app_path}/tmp/prometheus/*.bin"].each do |file_path|
+    File.unlink(file_path)
+  end
+end
 
 prometheus = Prometheus::Client.registry
 
 $metrics = {
-  ratelimit_remaining: prometheus.gauge(:ratelimit_remaining, "Remaining GitHub ratelimit."),
+  ratelimit_remaining: prometheus.gauge(:ratelimit_remaining, store_settings: store_settings, docstring: "Remaining GitHub ratelimit."),
 }

config/puma.rb

@@ -23,3 +23,12 @@
 if ENV["LOG_ENABLED"]
   stdout_redirect("#{app_path}/log/puma-stdout.log", "#{app_path}/log/puma-stderr.log", true)
 end
+
+if ENV["WEB_CONCURRENCY"]
+  on_worker_shutdown do |index|
+    # Delete stale metric files on worker shutdown
+    Dir["#{app_path}/tmp/prometheus/*___#{Process.pid}.bin"].each do |file_path|
+      File.unlink(file_path)
+    end
+  end
+end