add custom collector for mampf

TODO: caching

MONITORING.md

@@ -3,7 +3,7 @@
 ## Getting started (development mode): Setting up prometheus & grafana
 
 0. Start prometheus_exporter in the mampf container
-`sudo docker-compose exec mampf prometheus_exporter -b 0.0.0.0`
+`sudo docker-compose exec mampf prometheus_exporter -b 0.0.0.0 -a lib/collectors/mampf_collector.rb `
 1. Setup prometheus in development
 
 ```sh
@@ -27,4 +27,8 @@ grafana/grafana
 3. Now visit localhost:2345 and configure the datasource (`prometheus:9090`)
 4.  Setup the dashboard, interisting metrics:
   - `rate(ruby_collector_sessions_total[5m])`
-  - `rate(ruby_http_requests_total[5m])`
+  - `rate(ruby_http_requests_total[5m])`
+  - `ruby_user_count`: Number of users in the DB
+  - `ruby_uploaded_medium_count`: Number of Media
+  - `ruby_tag_count`: Number of Tags
+  - `ruby_submissions_count`: Number of Submissions

docker/development/prometheus.yml

@@ -0,0 +1,24 @@
+global:
+  scrape_interval:     15s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
+  evaluation_interval: 15s # Evaluate rules every 15 seconds. The default is every 1 minute.
+  # scrape_timeout is set to the global default (10s).
+
+# Alertmanager configuration
+
+# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
+
+# A scrape configuration containing exactly one endpoint to scrape:
+# Here it's Prometheus itself.
+scrape_configs:
+  # The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
+  - job_name: 'mampf'
+
+    # Override the global default and scrape targets from this job every 5 seconds.
+    scrape_interval: 5s
+    scrape_timeout:  5s
+
+    # metrics_path defaults to '/metrics'
+    # scheme defaults to 'http'.
+
+    static_configs:
+      - targets: ['mampf:9394']

lib/collectors/mampf_collector.rb

@@ -0,0 +1,25 @@
+unless defined? Rails
+    require File.expand_path("../../../config/environment", __FILE__)
+end
+class MampfCollector < PrometheusExporter::Server::TypeCollector
+    def initialize
+    end
+
+    def collect(obj)
+    end
+    def type
+        "mampf"
+    end
+
+    def metrics
+        user_count_gauge = PrometheusExporter::Metric::Gauge.new('user_count', 'number of users in the app')
+        user_count_gauge.observe User.count
+        medium_count_gauge = PrometheusExporter::Metric::Gauge.new('uploaded_medium_count', 'number of media')
+        medium_count_gauge.observe Medium.count
+        tag_count_gauge = PrometheusExporter::Metric::Gauge.new('tag_count', 'number of tags')
+        tag_count_gauge.observe Tag.count
+        submissions_count_gauge = PrometheusExporter::Metric::Gauge.new('submissions_count', 'number of submissions')
+        submissions_count_gauge.observe Submission.count
+        [user_count_gauge, medium_count_gauge,tag_count_gauge, submissions_count_gauge]
+      end
+  end