# PROMETHEUS CHEAT SHEET
Last Updated: 2026-05-11 14:44:00

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## Architecture Quick Reference
Central server runs:
- Prometheus → port 9090
- Grafana     → port 3000
- Alertmanager → port 9093

Each remote server runs:
- Node Exporter → port 9100

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## 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 |

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## 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
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### Debugging
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## prometheus.yml Skeleton
```yaml
global:
  scrape_interval: 15s
scrape_configs:
  - job_name: "example_job"
    static_configs:
      - targets: ["IP:PORT"]
```

## alertmanager.yml Skeleton
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## Alert Rule Skeleton
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## Node Exporter systemd service
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## PromQL Quick Reference
### My 7 servers queries
[Empty]

### Aggregation
[Empty]

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## Alert Rules For 7 Servers
[Empty]

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## Troubleshooting Decision Tree
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## Common Errors and Fixes
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