Port 9090 (TCP) — Prometheus UI + API

Enterno.io Editorial Team

Port 9090: Prometheus UI + API

By Anatoly Oshmanovsky · Updated Apr 18, 2026

Key idea:

Port 9090 (TCP) is the standard for Prometheus UI + API. Prometheus — TSDB for metrics. Port 9090 — web UI + HTTP API for PromQL queries. Standard monitoring stack component (with Grafana + Alertmanager).

Below: what uses this port, security considerations, online check, FAQ.

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What runs on this port

Prometheus UI + API

Prometheus — TSDB for metrics. Port 9090 — web UI + HTTP API for PromQL queries. Standard monitoring stack component (with Grafana + Alertmanager).

Security considerations

Prometheus without auth = anonymous access to every metric (can leak sensitive info like DB query duration, user IDs in histogram labels). Basic auth via nginx reverse proxy or OAuth2 proxy.

Check this port online

Check port online →

Enterno.io Ping + Port checker tests TCP reachability of any port from 3 regions (Moscow / Frankfurt / Virginia).

ICMP PingHost availability and latency

Port ScannerOpen TCP port detection

LatencyResponse time in milliseconds

Packet LossPercentage of dropped packets

Why teams trust us

ICMP+TCP

check protocols

key ports scanned

<2s

result

regions

How it works

Enter IP or domain

ICMP packets sent

Latency & packet loss shown

How Do Ping and Port Scanning Work?

Ping sends ICMP packets to a host and measures response time. Port scanning checks which TCP ports are open and accepting connections — helping diagnose serviceavailability issues.

Configurable Ping

Choose packet count (3, 4, 6, 10). Stats: min/avg/max latency and packet loss.

Common Port Scanner

Check 14 key ports: HTTP, HTTPS, SSH, FTP, SMTP, MySQL, PostgreSQL, and more.

Cloud-Based Check

Testing from our server — see site availability from outside, not just your local network.

Uptime Monitoring

Need constant monitoring? Create a monitor — checks every minute with notifications.

Who uses this

DevOps

availability diagnosis

Network engineers

TCP port scanning

Developers

connection debugging

SRE

basic health check

Common Mistakes

❌

ICMP blocked = server is downMany servers block ICMP. Ping fails but site works — check ports instead.

❌

High ping = server problemLatency depends on geography. 150ms between continents is normal, not an error.

❌

Closed ports — cause for alarmClosed ports of unused services are good. Unnecessary open ports are a risk.

❌

One check = sufficientNetworks are unstable. A single timeout ≠ a problem. Check multiple times or set up monitoring.

Best Practices

✓

Combine ping and port checksPing shows host availability, ports show specific service availability. Use both.

✓

Check from different locationsThe problem may be local. A cloud test shows the real picture.

✓

Close unused portsEvery open port is a potential attack vector. Keep only necessary ports open.

✓

Set up monitoringManual checks do not scale. Set up automated monitoring with notifications.

Get more with a free account

Ping check history, host availability monitoring and downtime alerts.

Frequently Asked Questions

Is port 9090 open by default?

No, modern cloud providers (AWS, Google Cloud, Yandex) close all incoming ports by default. You must explicitly allow port 9090 in a Security Group or firewall.

How to check if port 9090 is reachable?

Use <a href="/en/ping">Enterno Ping + Port Checker</a>. Or in shell: <code>nc -vz example.com 9090</code>.

Is port 9090 safe to expose?

Depends on the service. Prometheus UI + API should never be exposed publicly without authentication + TLS. See <a href="/en/s/research-open-ports-exposure-2026">our 2026 exposure research</a>.