Substrate binds JSON-RPC to loopback and makes opening it deliberately
awkward, which is correct for a validator. rpc_expose in the node matrix
takes the complete flag string; empty keeps it on loopback.
--rpc-methods safe is the load-bearing flag. It permits every state read
and author_submitExtrinsic (signed, so no key exposure) while blocking
author_rotateKeys, system_addReservedPeer and the rest. --rpc-methods
auto happens to downgrade once listening externally, but relying on that
makes the safety depend on a flag nobody wrote down.
The firewalld rich rule is scoped to the node's own /16, derived from
its own resolved address at deploy time -- so no subnet literal enters
this repo and the rule follows the host between sites.
Loopback is whitelisted from rate limiting because the arena exporter
runs beside the node and makes ~4 calls every 2s, which is 120/min --
enough to throttle itself against a naive limit.
validate now asserts the bind matches intent in both directions: nothing
listening while rpc_expose is set is a failure, and loopback-only is
reported as configuration rather than silence.
