Add possibility for setting prefix on custom metrics, solves #49

README.md

@@ -754,6 +754,30 @@ ruby_web_requests{hostname="app-server-01",route="test/route"} 1
 ruby_web_requests{hostname="app-server-01"} 1
 ```
 
+It is also possible to add a custom prefix to each counter instance.
+Same as above but with a custom prefix overriding the global prefix.
+```ruby
+# Specify global prefix for metric names
+PrometheusExporter::Metric::Base.default_prefix = "ruby"
+
+# Specify default labels for metrics
+PrometheusExporter::Metric::Base.default_labels = { "hostname" => "app-server-01" }
+
+# Counter instance with custom prefix for this metric
+counter = PrometheusExporter::Metric::Counter.new("web_requests", "number of web requests", "my_custom_prefix")
+
+counter.observe(1, route: 'test/route')
+counter.observe
+```
+
+This will output these metrics
+```
+# HELP my_custom_prefix_web_requests number of web requests
+# TYPE my_custom_prefix_web_requests counter
+my_custom_prefix_web_requests{hostname="app-server-01",route="test/route"} 1
+my_custom_prefix_web_requests{hostname="app-server-01"} 1
+```
+
 ### Exporter Process Configuration
 
 When running the process for `prometheus_exporter` using `bin/prometheus_exporter`, there are several configurations that

lib/prometheus_exporter/metric/base.rb

@@ -25,9 +25,10 @@ def self.default_labels
 
     attr_accessor :help, :name, :data
 
-    def initialize(name, help)
+    def initialize(name, help, opts = {})
       @name = name
       @help = help
+      @opts = opts
     end
 
     def type
@@ -62,7 +63,8 @@ def from_json(json)
     end
 
     def prefix(name)
-      Base.default_prefix + name
+      pfx = @opts && @opts.key?(:prefix) ? @opts[:prefix] : Base.default_prefix
+      pfx + name
     end
 
     def labels_text(labels)

lib/prometheus_exporter/metric/counter.rb

@@ -4,7 +4,7 @@ module PrometheusExporter::Metric
   class Counter < Base
     attr_reader :data
 
-    def initialize(name, help)
+    def initialize(name, help, opts = {})
       super
       reset!
     end

lib/prometheus_exporter/metric/gauge.rb

@@ -4,7 +4,7 @@ module PrometheusExporter::Metric
   class Gauge < Base
     attr_reader :data
 
-    def initialize(name, help)
+    def initialize(name, help, opts = {})
       super
       reset!
     end

lib/prometheus_exporter/metric/histogram.rb

@@ -6,7 +6,7 @@ class Histogram < Base
     DEFAULT_BUCKETS = [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5.0, 10.0].freeze
 
     def initialize(name, help, opts = {})
-      super(name, help)
+      super
       @buckets = (opts[:buckets] || DEFAULT_BUCKETS).sort.reverse
       reset!
     end

lib/prometheus_exporter/metric/summary.rb

@@ -9,7 +9,7 @@ class Summary < Base
     attr_reader :estimators, :count, :total
 
     def initialize(name, help, opts = {})
-      super(name, help)
+      super
       reset!
       @quantiles = opts[:quantiles] || DEFAULT_QUANTILES
     end

lib/prometheus_exporter/server/collector.rb

@@ -81,9 +81,9 @@ def register_metric_unsafe(obj)
       metric =
         case obj["type"]
         when "gauge"
-          PrometheusExporter::Metric::Gauge.new(name, help)
+          PrometheusExporter::Metric::Gauge.new(name, help, opts)
         when "counter"
-          PrometheusExporter::Metric::Counter.new(name, help)
+          PrometheusExporter::Metric::Counter.new(name, help, opts)
         when "summary"
           PrometheusExporter::Metric::Summary.new(name, help, opts)
         when "histogram"

test/metric/base_test.rb

@@ -48,6 +48,23 @@ module PrometheusExporter::Metric
       assert_equal(counter.to_prometheus_text, text)
     end
 
+    it "supports custom prefix" do
+      Base.default_prefix = 'notcustom_'
+      cp = Counter.new("a_counter", "my amazing counter", prefix: 'custom_prefix_')
+
+      cp.observe(2, baz: "bar")
+      cp.observe(223)
+
+      text = <<~TEXT
+        # HELP custom_prefix_a_counter my amazing counter
+        # TYPE custom_prefix_a_counter counter
+        custom_prefix_a_counter{baz="bar"} 2
+        custom_prefix_a_counter 223
+      TEXT
+
+      assert_equal(cp.to_prometheus_text, text)
+    end
+
     it "supports reset! for Gauge" do
 
       gauge = Gauge.new("test", "test")

test/server/collector_test.rb

@@ -237,6 +237,52 @@ def test_it_can_pass_options_to_histogram
     assert_equal(text, collector.prometheus_metrics_text)
   end
 
+  def test_it_can_pass_options_to_gauge
+    name = 'test_name'
+    help = 'test_help'
+    collector = PrometheusExporter::Server::Collector.new
+    json = {
+      type: :gauge,
+      help: help,
+      name: name,
+      keys: { key1: 'test1' },
+      opts: { prefix: 'custom_pfx_' },
+      value: 8
+    }
+    collector.process(json.to_json)
+
+    text = <<~TXT
+      # HELP custom_pfx_test_name test_help
+      # TYPE custom_pfx_test_name gauge
+      custom_pfx_test_name{key1=\"test1\"} 8
+    TXT
+
+    assert_equal(text, collector.prometheus_metrics_text)
+  end
+
+  def test_it_can_pass_options_to_counter
+    name = 'test_name'
+    help = 'test_help'
+    collector = PrometheusExporter::Server::Collector.new
+    json = {
+      type: :counter,
+      help: help,
+      name: name,
+      keys: { key1: 'test1' },
+      opts: { prefix: 'custom_pfx_' },
+      value: 18
+    }
+    collector.process(json.to_json)
+
+    text = <<~TXT
+      # HELP custom_pfx_test_name test_help
+      # TYPE custom_pfx_test_name counter
+      custom_pfx_test_name{key1=\"test1\"} 18
+    TXT
+
+    assert_equal(text, collector.prometheus_metrics_text)
+  end
+
   def test_it_can_collect_sidekiq_metrics
     collector = PrometheusExporter::Server::Collector.new
     client = PipedClient.new(collector)