Prometheus

Prometheus is the time-series monitoring standard. Pull-based metrics, PromQL queries, alerting rules, and Kubernetes-native discovery. CNCF-graduated, used at SoundCloud (where it was created), DigitalOcean, and 80% of Kubernetes deployments.

At a glance

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License Apache-2.0 Version 3.13.2 OS Ubuntu Server 24.04 LTS Min RAM 1 GB IP IPV4,IPV6

Access

Open https://<SERVER_IP>:9090 in your browser.
The certificate is self-signed, so your browser will display a certificate warning.
The Prometheus targets page is available at https://<SERVER_IP>:9090/targets.
Metrics are available at https://<SERVER_IP>:9090/metrics.

Prometheus is protected with HTTP Basic Authentication.

Username: admin
Password: stored in /root/.prometheus-credentials

The same authentication protects the web UI, API, and /metrics endpoint.

Important Files & Directories

Prometheus Config: /etc/prometheus/prometheus.yml
Web/TLS/Auth Config: /etc/prometheus/web-config.yml
TLS Certificates: /etc/prometheus/tls/
Prometheus Data: /var/lib/prometheus
Node Exporter Textfile Collector: /var/lib/node_exporter/textfile_collector
Credentials: /root/.prometheus-credentials
Prometheus Binary: /usr/local/bin/prometheus
Promtool: /usr/local/bin/promtool
Node Exporter Binary: /usr/local/bin/node_exporter
Prometheus Service: /etc/systemd/system/prometheus.service
Node Exporter Service: /etc/systemd/system/node_exporter.service

Service Management

Check Prometheus:

systemctl status prometheus

Restart Prometheus:

systemctl restart prometheus

View Prometheus logs:

journalctl -u prometheus -f

Check Node Exporter:

systemctl status node_exporter

Restart Node Exporter:

systemctl restart node_exporter

View Node Exporter logs:

journalctl -u node_exporter -f

Adding Targets

Edit /etc/prometheus/prometheus.yml:

vim /etc/prometheus/prometheus.yml

Validate the configuration:

promtool check config /etc/prometheus/prometheus.yml

Reload Prometheus:

curl -sS --cacert /etc/prometheus/tls/prometheus.crt \
  -u admin:<PASSWORD> \
  -X POST https://localhost:9090/-/reload

Retention

Prometheus is configured with:

Retention time: 30d
Maximum storage size: 10GB

Whichever limit is reached first is applied.

Notes

Grafana and Alertmanager are not installed. They can be added separately and connected to this Prometheus instance.
Metrics are retained for up to 30 days or 10 GB, whichever limit is reached first.
Custom host metrics can be added as .prom files under: /var/lib/node_exporter/textfile_collector

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