Short names with ephemeral ports versus long names with fixed distribution ports for cross-host Erlang clustering

Question

GoalRun distributed Erlang nodes across production hosts after local tests succeeded using short names and default ephemeral distribution ports.ConstraintProduction firewalls commonly allow EPMD on TCP 4369 but block the ephemeral TCP ports used for distribution data channels. Nodes started with -sname resolve on localhost but can fail across hosts when short-name DNS or interface binding differs. Nodes started with -name require a fully qualified domain name and consistent forward/reverse DNS on every host. Setting inet_dist_listen_min and inet_dist_listen_max pins listeners to a firewall-friendly range, but the range must match on all nodes and requires a VM restart. Short-name and long-name nodes cannot communicate in the same cluster.UncertaintyAssuming an OTP release where the kernel application exposes inet_dist_listen_min and inet_dist_listen_max, which approach fits hosts without guaranteed FQDN or uniform DNS: short names bound to a specific interface with a fixed port range, or long names with FQDN and the same fixed range?Can -sname nodes communicate across production hosts when each node binds to a different interface IP and distribution ports are restricted to a fixed range?Is -name with FQDN preferable when forward and reverse DNS cannot be guaranteed identical on every host?What is the safest migration path if local development used -sname but production requires cross-host long names?

Siddharth · Answer

Answer
For production hosts that cannot guarantee a consistent fully‑qualified domain name or uniform DNS, the reliable approach is to use short‑name nodes that are bound to a specific interface address and limited to a fixed distribution‑port range. This avoids reliance on DNS resolution while still satisfying firewall rules that permit only the EPMD port 4369 and a narrow range of distribution ports.
Confirmed facts

OTP 13 or newer exposes the kernel options inet_dist_listen_min and inet_dist_listen_max, allowing you to pin distribution sockets to a static TCP range.
Firewalls typically allow TCP 4369 (EPMD) but block the dynamic ephemeral ports used by default distribution channels.
Short‑name nodes (-sname) resolve via EPMD on the local node name; they can be forced to a particular interface by appending the address (e.g., node@10.0.0.5) while still using the fixed port range.
Long‑name nodes (-name) require the full FQDN to be resolvable forward and reverse on every host; missing or mismatched DNS records prevent cluster formation.

Steps to make short‑name nodes work across hosts

Verify the OTP version: erl -version – must be 13 or newer.
Choose a firewall‑friendly port range (for example 40000‑50000) and set it on every node: erl -kernel inet_dist_listen_min 40000 inet_dist_listen_max 50000 (or via the node start script).
Ensure each host’s distribution socket listens on the chosen range; check with netstat -anp | grep 40000 or ss -ltnp.
Start each node with the address suffix that matches the interface used for inter‑host traffic, e.g. erl -sname node@10.0.0.5 -setcookie secret.
Test connectivity between two hosts: erl -noshell -s init stop -setcookie secret -s erlang -eval net_adm:ping("node@10.0.0.6").

Missing diagnostic detail: Is there a single reachable IP address on each production host that can be used for Erlang distribution, or do hosts have multiple NICs?

Short names with ephemeral ports versus long names with fixed distribution ports for cross-host Erlang clustering

Goal

Constraint

Uncertainty

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Answer

Confirmed facts

Steps to make short‑name nodes work across hosts

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