You can configure the inet dns resolver to never resolve anything. That way only ip addresses will be possible to use.
For example:
echo "{lookup,[]}." > ./erl_inetrc
ERL_INETRC=./erl_inetrc iex
Erlang/OTP 27 [RELEASE CANDIDATE 2] [erts-14.2.3] [source-f7fa414e3e] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]
Interactive Elixir (1.17.0-dev) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> :gen_tcp.connect(~c"localhost",80,[])
{:error, :nxdomain}
You can read more about how to configure inetrc here: Inet Configuration — OTP 29.0.2 (erts 17.0.2)
