Port 2379 (TCP) — etcd client: what it is, how to check

Port 2379 etcd client · TCP

etcd client port: the key-value store that holds the entire state of a Kubernetes cluster (every secret included) and of CoreDNS, Patroni and others.

Port	2379
Transport	TCP
Service	etcd client — Kubernetes datastore
Category	Infrastructure
Range	registered (1024–49151)
Encrypted	Yes, always (TLS or equivalent)
Exposure	Private network or VPN only

What runs on port 2379

etcd client port: the key-value store that holds the entire state of a Kubernetes cluster (every secret included) and of CoreDNS, Patroni and others. Read access to etcd is cluster admin. Kubernetes distributions set it up with TLS client certificates on the control-plane nodes only.

Software that uses it: etcd · Kubernetes control plane · Patroni (PostgreSQL HA) · Calico, Cilium (optional backends)

Should port 2379 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

etcdctl --endpoints=https://host:2379 --cacert ... --cert ... --key ... endpoint health is the standard check.
Back up etcd (etcdctl snapshot save); it is the one thing you cannot rebuild from the nodes.

Check port 2379

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :2379'
sudo lsof -i :2379

# from another machine: is it reachable?
nc -zv host 2379
nmap -p 2379 host
curl -v telnet://host:2379      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 2379

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 2379 proto tcp
sudo ufw deny 2379/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 2379 accept
nft add rule inet filter input tcp dport 2379 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 2379 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 2379 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=2379 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 2379" with no source is just "open".

Related ports

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions

Is port 2379 TCP or UDP?

TCP. etcd client is a connection-oriented protocol; there is no UDP service on 2379 by default (a scanner reporting UDP 2379 open is usually seeing a filtered port).

Is port 2379 encrypted?

Yes, always (TLS or equivalent). The port number does not make it safe by itself: certificate validation, authentication and patching still decide.

How do I check whether port 2379 is open?

On the server, ss -ltnp (or -lunp for UDP) shows whether something listens on 2379 and which process. From another machine, nc -zv host 2379 or nmap -p 2379 host tests reachability. "Open" in a scan means something answered; a firewall usually makes the port filtered (no answer) rather than closed (RST).

Can etcd client run on a different port?

Yes; the number is a convention, not a requirement. Changing it reduces log noise from scanners but does not add security, and every client, firewall rule and monitoring check then needs the new number. Keep the default unless you have a concrete reason.