Prometheus
What is Port 9090?
Port 9090 is the default port for Prometheus, the leading open-source monitoring and alerting system. Prometheus collects time-series metrics from configured targets at given intervals, evaluates rule expressions, displays results, and can trigger alerts. Originally built at SoundCloud and now a graduated CNCF (Cloud Native Computing Foundation) project, Prometheus has become the de facto standard for Kubernetes and cloud-native monitoring. Prometheus uses a pull model — it scrapes metrics from HTTP endpoints exposed by applications and infrastructure. Port 9090 serves both the Prometheus web UI (for querying and graphing metrics via PromQL) and the API that Grafana and other tools use to retrieve data. The Prometheus ecosystem includes exporters for virtually every service and platform.
Common Uses
- Monitoring system metrics collection and storage
- PromQL query interface for metrics analysis
- Alerting rule evaluation and notification
- Grafana data source for dashboards
Technical Details
Copy-paste commands to check port 9090 (Prometheus) from your terminal
Test connectivity
nc -zv example.com 9090
curl -v --max-time 5 http://example.com:9090/
telnet example.com 9090
nmap -p 9090 -sV example.com
(echo > /dev/tcp/example.com/9090) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 9090/tcp
sudo iptables -A INPUT -p tcp --dport 9090 -j ACCEPT
sudo firewall-cmd --permanent --add-port=9090/tcp && sudo firewall-cmd --reload
Security Considerations
Prometheus has no built-in authentication by default. Use a reverse proxy with authentication for the web UI. Restrict scrape targets to authorized endpoints. Protect the /api/v1 endpoints. In Kubernetes, use network policies to restrict Prometheus access. Be aware that Prometheus metrics may contain sensitive information about your infrastructure.
Popular Ports Reference
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