arsnova.cards: Prometheus, MongoDB, Meteor

main.js.patch

diff --git a/server/main.js b/server/main.js
index 4c6ddc6e..11b1c792 100644
--- a/server/main.js
+++ b/server/main.js
@@ -22,4 +22,15 @@ import "../imports/api/userdata.js";
 import "../imports/api/webPushSubscriptions.js";
 import "./leitner.js";
 
+// npm install prom-client
+const promClient = require("prom-client");
+promClient.collectDefaultMetrics();
+
+const register = promClient.register;
+// Listen to incoming HTTP requests (can only be used on the server).
+WebApp.connectHandlers.use('/metrics', (req, res, next) => {
+    res.writeHead(200, {'Content-Type': register.contentType});
+    res.end(register.metrics());
+});
+
 WebApp.addHtmlAttributeHook(() => ({lang: 'de', charset: 'utf-8'}));

prometheus.yml

# my global config
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
alerting:
  alertmanagers:
  - static_configs:
    - targets:
      # - alertmanager:9093

# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
rule_files:
  # - "first_rules.yml"
  # - "second_rules.yml"

# 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: 'prometheus'

    # metrics_path defaults to '/metrics'
    # scheme defaults to 'http'.

    static_configs:
    - targets: ['localhost:9090']

  - job_name: 'mongodb'
    static_configs:
    - targets: ['localhost:9001']

  - job_name: 'cards'
    static_configs:
    - targets: ['localhost:3000']

start_mongodb_exporter.sh

MONGODB_URL=mongodb://127.0.0.1:3001/meteor ./mongodb_exporter-linux-amd64