Feature: Add Dalli::Client memcache metrics for web_collector

README.md

@@ -213,13 +213,14 @@ Rails.application.middleware.unshift PrometheusExporter::Middleware, instrument:
 
 #### Metrics collected by Rails integration middleware
 
-| Type    | Name                                   | Description                                                 |
-| ---     | ---                                    | ---                                                         |
-| Counter | `http_requests_total`                  | Total HTTP requests from web app                            |
-| Summary | `http_request_duration_seconds`        | Time spent in HTTP reqs in seconds                          |
-| Summary | `http_request_redis_duration_seconds`¹ | Time spent in HTTP reqs in Redis, in seconds                |
-| Summary | `http_request_sql_duration_seconds`²   | Time spent in HTTP reqs in SQL in seconds                   |
-| Summary | `http_request_queue_duration_seconds`³ | Time spent queueing the request in load balancer in seconds |
+| Type    | Name                                      | Description                                                 |
+| ---     | ---                                       | ---                                                         |
+| Counter | `http_requests_total`                     | Total HTTP requests from web app                            |
+| Summary | `http_request_duration_seconds`           | Time spent in HTTP reqs in seconds                          |
+| Summary | `http_request_redis_duration_seconds`¹    | Time spent in HTTP reqs in Redis, in seconds                |
+| Summary | `http_request_sql_duration_seconds`²      | Time spent in HTTP reqs in SQL in seconds                   |
+| Summary | `http_request_queue_duration_seconds`³    | Time spent queueing the request in load balancer in seconds |
+| Summary | `http_request_memcache_duration_seconds`⁴ | Time spent in HTTP reqs in Memcache in seconds              |
 
 All metrics have a `controller` and an `action` label.
 `http_requests_total` additionally has a (HTTP response) `status` label.
@@ -268,6 +269,7 @@ ruby_http_request_duration_seconds{path="/api/v1/teams/:id",method="GET",status=
 ¹) Only available when Redis is used.
 ²) Only available when Mysql or PostgreSQL are used.
 ³) Only available when [Instrumenting Request Queueing Time](#instrumenting-request-queueing-time) is set up.
+⁴) Only available when Dalli is used.
 
 #### Activerecord Connection Pool Metrics
 

lib/prometheus_exporter/middleware.rb

@@ -31,6 +31,9 @@ def initialize(app, config = { instrument: :alias_method, client: nil })
         MethodProfiler.patch(Mysql2::Statement, [:execute], :sql, instrument: config[:instrument])
         MethodProfiler.patch(Mysql2::Result, [:each], :sql, instrument: config[:instrument])
       end
+      if defined? Dalli::Client
+        MethodProfiler.patch(Dalli::Client, %i[delete fetch get add set], :memcache, instrument: config[:instrument])
+      end
     end
   end
 

lib/prometheus_exporter/server/web_collector.rb

@@ -9,6 +9,7 @@ def initialize
       @http_request_redis_duration_seconds = nil
       @http_request_sql_duration_seconds = nil
       @http_request_queue_duration_seconds = nil
+      @http_request_memcache_duration_seconds = nil
     end
 
     def type
@@ -48,6 +49,11 @@ def ensure_metrics
           "Time spent in HTTP reqs in SQL in seconds."
         )
 
+        @metrics["http_request_memcache_duration_seconds"] = @http_request_memcache_duration_seconds = PrometheusExporter::Metric::Base.default_aggregation.new(
+          "http_request_memcache_duration_seconds",
+          "Time spent in HTTP reqs in Memcache in seconds."
+        )
+
         @metrics["http_request_queue_duration_seconds"] = @http_request_queue_duration_seconds = PrometheusExporter::Metric::Base.default_aggregation.new(
           "http_request_queue_duration_seconds",
           "Time spent queueing the request in load balancer in seconds."
@@ -70,6 +76,9 @@ def observe(obj)
         if sql = timings["sql"]
           @http_request_sql_duration_seconds.observe(sql["duration"], labels)
         end
+        if memcache = timings["memcache"]
+          @http_request_memcache_duration_seconds.observe(memcache["duration"], labels)
+        end
       end
       if queue_time = obj["queue_time"]
         @http_request_queue_duration_seconds.observe(queue_time, labels)

test/middleware_test.rb

@@ -164,6 +164,17 @@ def test_patch_called_with_prepend_instrument
         mock.verify
       end
     end
+
+    Object.stub_const(:Dalli, Module) do
+      ::Dalli.stub_const(:Client) do
+        mock = Minitest::Mock.new
+        mock.expect :call, nil, [Dalli::Client, Array, :memcache, { instrument: :prepend }]
+        ::PrometheusExporter::Instrumentation::MethodProfiler.stub(:patch, mock) do
+          configure_middleware(instrument: :prepend)
+        end
+        mock.verify
+      end
+    end
   end
 
   def test_patch_called_with_alias_method_instrument
@@ -204,5 +215,16 @@ def test_patch_called_with_alias_method_instrument
         mock.verify
       end
     end
+
+    Object.stub_const(:Dalli, Module) do
+      ::Dalli.stub_const(:Client) do
+        mock = Minitest::Mock.new
+        mock.expect :call, nil, [Dalli::Client, Array, :memcache, { instrument: :alias_method }]
+        ::PrometheusExporter::Instrumentation::MethodProfiler.stub(:patch, mock) do
+          configure_middleware(instrument: :alias_method)
+        end
+        mock.verify
+      end
+    end
   end
 end

test/server/web_collector_test.rb

@@ -32,7 +32,7 @@ def test_collecting_metrics_without_specific_timings
 
     metrics = collector.metrics
 
-    assert_equal 5, metrics.size
+    assert_equal 6, metrics.size
   end
 
   def test_collecting_metrics
@@ -47,6 +47,10 @@ def test_collecting_metrics
           duration: 0.03,
           count: 4
         },
+        "memcache" => {
+          duration: 0.02,
+          count: 1
+        },
         "queue" => 0.03,
         "total_duration" => 1.0
       },
@@ -58,7 +62,7 @@ def test_collecting_metrics
     )
 
     metrics = collector.metrics
-    assert_equal 5, metrics.size
+    assert_equal 6, metrics.size
   end
 
   def test_collecting_metrics_with_custom_labels
@@ -77,7 +81,7 @@ def test_collecting_metrics_with_custom_labels
 
     metrics = collector.metrics
 
-    assert_equal 5, metrics.size
+    assert_equal 6, metrics.size
     assert(metrics.first.metric_text.include?('http_requests_total{controller="home",action="index",service="service1",status="200"} 1'))
   end
 
@@ -98,7 +102,7 @@ def test_collecting_metrics_merging_custom_labels_and_status
 
     metrics = collector.metrics
 
-    assert_equal 5, metrics.size
+    assert_equal 6, metrics.size
     assert(metrics.first.metric_text.include?('http_requests_total{controller="home",action="index",service="service1",status="200"} 1'))
   end
 
@@ -117,6 +121,10 @@ def test_collecting_metrics_in_histogram_mode
           duration: 0.03,
           count: 4
         },
+        "memcache" => {
+          duration: 0.02,
+          count: 1
+        },
         "queue" => 0.03,
         "total_duration" => 1.0,
       },
@@ -132,7 +140,7 @@ def test_collecting_metrics_in_histogram_mode
     metrics = collector.metrics
     metrics_lines = metrics.map(&:metric_text).flat_map(&:lines)
 
-    assert_equal 5, metrics.size
+    assert_equal 6, metrics.size
     assert_includes(metrics_lines, "http_requests_total{controller=\"home\",action=\"index\",service=\"service1\",status=\"200\"} 1")
     assert_includes(metrics_lines, "http_request_duration_seconds_bucket{controller=\"home\",action=\"index\",service=\"service1\",le=\"+Inf\"} 1\n")
   end