extended_bin: Support 'inet_dist_use_interface' in vm.args #891

weiss · 2021-11-09T10:41:41Z

Support specifying the kernel option inet_dist_use_interface in the vm.args file. If ERL_DIST_PORT is set while using Erlang/OTP 23 or newer, make sure to hand over the inet_dist_use_interface address to erl_call's -address option.

My own use case is binding the VM to 127.0.0.1 (if not actually running a cluster) and still being able to use ERL_DIST_PORT.

tsloughter · 2021-11-11T23:49:37Z

Thanks. But weird that the command line kernel option is a tuple and not just an ip string. I don't like having to parse that in shell script :( but I guess no way around it.

Support specifying the kernel option 'inet_dist_use_interface' in the vm.args file. If ERL_DIST_PORT is set while using Erlang/OTP 23+, make sure to hand over the 'inet_dist_use_interface' address to erl_call.

weiss · 2021-11-12T11:03:47Z

I don't like having to parse that in shell script :(

Yes, ugliness 😒

I guess no way around it.

I see no way, except maybe giving up on the idea of specifying the address to use by the main node and by erl_call in a single place. I.e., just add some RPC_ADDRESS (or whetever) variable for erl_call to use, and let the user specify both inet_dist_user_interface and that new variable. (Would be good enough for me personally, and would allow for keeping the inet_dist_user_interface setting in sys.config, where it looks less ugly to me. But would be ugly in a different way.)

weiss · 2021-12-23T15:59:42Z

I see no way

Well I guess another way would be using Erlang instead, e.g. something along the following lines. But it's probably preferable not to spin up the VM for that job.

# Convert {127,0,0,1} to 127.0.0.1
addr_tuple_to_str() {
    addr="$1"
    code="catch io:format(\"~s\", [inet:ntoa($addr)]), halt()."
    result="$("$BINDIR/erl" -noinput -boot no_dot_erlang -eval "$code")"

    if [ -n "$result" ]; then
        printf '%s' "$result"
    else
        echo "Cannot parse IP address tuple: '$addr'" >&2
    fi
}

tsloughter · 2021-12-31T12:45:58Z

Oh, duh, its using a tuple because its using -kernel ... so it is not an exposed erl arg like my original thinking.

tsloughter · 2021-12-31T12:57:45Z

priv/templates/extended_bin

@@ -674,8 +690,17 @@ EPMD_MODULE="$(grep '^-epmd_module' "$VMARGS_PATH" || true)"
 if [ "$EPMD_MODULE" ]; then
    DIST_ARGS="${DIST_ARGS} ${EPMD_MODULE}"
 fi
+INET_DIST_USE_INTERFACE="$(grep '^-kernel  *inet_dist_use_interface' "$VMARGS_PATH" || true)"


Why the *?

Just to cope with the user adding superflous whitespace in vm.args. I can totally live without that 😄

I mean additional spaces between -kernel and inet_dist_use_interface.

I'd at least use it in quotes if it were possible, to clarify the intent.

Sorry I probably need more coffee, you'd add quotes where exactly?

Ah nevermind, I misread the regex and nested argument. The quotes are already there. I had initially read it as 'grep ...' rather than grep '...'

weiss · 2021-12-31T12:57:54Z

Oh, duh, its using a tuple because its using -kernel ... so it is not an exposed erl arg like my original thinking.

Yes. That's the (only) way of telling the VM to dist-listen on localhost, I think? Which doesn't seem like an obscure use case to me? (I just want to use the extended start script for controlling my daemon, rather than running an actual cluster.)

tsloughter · 2021-12-31T12:58:53Z

priv/templates/extended_bin


 if [ "$ERL_DIST_PORT" ]; then
+    if [ "$INET_DIST_USE_INTERFACE" ]; then
+        ADDRESS="$(addr_tuple_to_str "${INET_DIST_USE_INTERFACE#*inet_dist_use_interface }"):$ERL_DIST_PORT"


Not sure what is going on here with ${INET_DIST_USE_INTERFACE#*inet_dist_use_interface }?

And have to make sure it is posix shell compliant? Not bash.

Oh, looks like shellcheck caught something else so this must have passed and thus work ok with posix shell.

But I still don't know what it is doing :)

${INET_DIST_USE_INTERFACE#*inet_dist_use_interface }

At that point INET_DIST_USE_INTERFACE is e.g. -kernel inet_dist_use_interface {127,0,0,1}. The #*inet_dist_use_interface thing is stripping everything up to the actual address tuple.

And have to make sure it is posix shell compliant?

It is.

Shall I try to come up with something less magic, more readable?

Ahh, no, this is good and makes sense. I was misreading (still early :) and thought it was like ${ADDRESS#*inet_dist_use_interface } so had no idea why inet_dist_use_interface was involved when I thought it was already just the address :)

tsloughter · 2021-12-31T13:19:17Z

Not obscure at all. Something we should have supported for using the shell, rpc, etc stuff a long long time ago :).

I think this is good, just being cautious since tiny changes in this particular code has broken certain users before. It is a mess.

weiss · 2021-12-31T13:22:30Z

just being cautious since tiny changes in this particular code has broken certain users before. It is a mess.

Totally makes sense, I'm very happy with such detailed review! 👍

Specify 'inet_dist_use_interface' in vm.args rather than sys.config. This lets the extended start script parse the IP address, which allows for specifying the environment variable ERL_DIST_PORT to avoid using EPMD, which is now a documented use case. This feature requires at least Erlang/OTP 23.1 and Rebar3 3.18.0. For details, see: https://blog.erlware.org/epmdlessless/ erlware/relx#891

weiss force-pushed the support-dist-addr branch 2 times, most recently from 7697a70 to c1722bc Compare November 9, 2021 11:05

extended_bin: Support 'inet_dist_use_interface'

36137dd

Support specifying the kernel option 'inet_dist_use_interface' in the vm.args file. If ERL_DIST_PORT is set while using Erlang/OTP 23+, make sure to hand over the 'inet_dist_use_interface' address to erl_call.

weiss force-pushed the support-dist-addr branch from c1722bc to 36137dd Compare November 12, 2021 09:15

weiss mentioned this pull request Dec 28, 2021

Eturnal not starting on Rocky Linux 8.5 processone/eturnal#19

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tsloughter reviewed Dec 31, 2021

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tsloughter approved these changes Dec 31, 2021

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tsloughter merged commit 14f80c9 into erlware:master Dec 31, 2021

weiss deleted the support-dist-addr branch December 31, 2021 19:50

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extended_bin: Support 'inet_dist_use_interface' in vm.args #891

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extended_bin: Support 'inet_dist_use_interface' in vm.args #891

extended_bin: Support 'inet_dist_use_interface' in vm.args #891

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weiss commented Nov 9, 2021

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tsloughter commented Dec 31, 2021

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