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+# PROMETHEUS CHEAT SHEET
+Last Updated: 2026-05-11 14:44:00
+
+---
+
+## Architecture Quick Reference
+Central server runs:
+- Prometheus → port 9090
+- Grafana     → port 3000
+- Alertmanager → port 9093
+
+Each remote server runs:
+- Node Exporter → port 9100
+
+---
+
+## Bridge Reference
+| Prometheus concept | MERN/Express equivalent |
+|---|---|
+| prometheus.yml | Express config / .env |
+| scrape_interval | setInterval() |
+| Node Exporter | /health endpoint |
+| job_name | route group name |
+| labels | MongoDB document fields |
+| PromQL | MongoDB query language |
+| rate() | calculating speed from counter |
+| Grafana | React frontend |
+| Alertmanager | nodemailer |
+| systemd service | PM2 process |
+| promtool check | ESLint |
+| recording rule | database view |
+| federation | API gateway pattern |
+
+---
+
+## Essential Commands
+### Install sequence
+wget <url> → Downloads file from internet
+tar -xvf <filename> → Unzips a .tar.gz file
+sudo useradd --no-create-home --shell /bin/false prometheus → Creates restricted user
+sudo mkdir <folder_path> → Creates a new folder as admin
+sudo chown user:group <folder_path> → Changes the owner of a folder
+sudo cp <file> <destination> → Copies a file to a new location
+
+### systemd commands
+sudo systemctl daemon-reload → Reloads Linux after creating a new .service file
+sudo systemctl start <service> → Turns a service ON right now
+sudo systemctl enable <service> → Tells Linux to turn it on automatically after reboot
+sudo systemctl status <service> → Checks if the service is running or crashed
+
+### Validation
+[Empty]
+
+### Debugging
+[Empty]
+
+---
+
+## prometheus.yml Skeleton
+```yaml
+global:
+  scrape_interval: 15s
+scrape_configs:
+  - job_name: "example_job"
+    static_configs:
+      - targets: ["IP:PORT"]
+```
+
+## alertmanager.yml Skeleton
+[Empty]
+
+## Alert Rule Skeleton
+[Empty]
+
+## Node Exporter systemd service
+[Empty]
+
+---
+
+## PromQL Quick Reference
+### My 7 servers queries
+[Empty]
+
+### Aggregation
+[Empty]
+
+---
+
+## Alert Rules For 7 Servers
+[Empty]
+
+---
+
+## Troubleshooting Decision Tree
+[Empty]
+
+---
+
+## Common Errors and Fixes
+[Empty]