Re: Questions about "erl -epmd_start false"

Hi Shino,

No worries at all for the lag and thanks a lot for the explanation!

Cheers,
Jérôme

Le mar. 12 janv. 2021 à 01:44, Shunichi Shinohara <[email protected]> a
écrit :

> Hi Jérôme,
>
> Sorry for the late reply. (new-year-holiday-lag)
>
> > Could you describe a case when the epmd daemon is running but you
> > wouldn't want the registration to happen? In your original question,
> > what is the actual issue with the node being registered when epmd is
> > running?
>
> Our company sells a package software written in Erlang. If epmd daemon
> process is unnecessary, user operation will be simpler.
> # However, it makes very little difference and is not feature related.
> # So, eliminating epmd is not a blocking issue but just nice-to-have.
>
> On the other hand, I want to keep the difference between my development
> environment and users' production ones as little as possible. On my side,
> epmd is almost always running (e.g. erlang_ls processes use it.)
>
> To satisfy both, it's great that Erlang nodes do not register themselves
> even
> in the case epmd is running.
>
> Thanks,
> Shino
>
> 2021年1月1日(金) 0:37 Jérôme de Bretagne <[email protected]>:
>
>> You're welcome, Shino.
>>
>> Could you describe a case when the epmd daemon is running but you
>> wouldn't want the registration to happen? In your original question,
>> what is the actual issue with the node being registered when epmd is
>> running?
>>
>> For anyone interested by the details, the code that triggers the
>> registration (via 'register_node') is found here:
>>
>> https://github.com/erlang/otp/blob/master/lib/kernel/src/erl_epmd.erl#L224-L245
>> and the 'erl_epmd_port' option is used only as a fallback when
>> 'do_register_node' doesn't succeed in registering with the epmd
>> daemon.
>>
>> With the default 'inet_tcp' distribution protocol, the call to
>> 'register_node' is currently mandatory in 'gen_listen' here:
>>
>> https://github.com/erlang/otp/blob/master/lib/kernel/src/inet_tcp_dist.erl#L93-L97
>>
>> With the 'gen_tcp_dist' alternative distribution protocol example, the
>> call to 'register_node' is also mandatory, this time in 'listen' here:
>>
>> https://github.com/erlang/otp/blob/master/lib/kernel/examples/gen_tcp_dist/src/gen_tcp_dist.erl#L86-L94
>> but it should be relatively easy to make a custom version that gives
>> the priority to the 'erl_epmd_port' option if preferred.
>>
>> Cheers,
>> Jérôme
>>
>>
>> Le mar. 22 déc. 2020 à 04:03, Shunichi Shinohara
>> <[email protected]> a écrit :
>> >
>> > Maybe there are anyone interested, discussion continues in github PR:
>> >   Document the -no_epmd option by JeromeDeBretagne · Pull Request #2945
>> · erlang/otp
>> >   https://github.com/erlang/otp/pull/2945
>> >
>> > Thanks for the PR, Jérôme!
>> >
>> > -----
>> > Shino
>> >
>> > 2020年12月21日(月) 10:11 Shunichi Shinohara <[email protected]>:
>> >>
>> >> Hi Jérôme,
>> >>
>> >> Thanks a lot for the useful information, it works like a charm!
>> >>
>> >> Thanks again,
>> >> Shino
>> >>
>> >>
>> >> 2020年12月18日(金) 17:50 Jérôme de Bretagne <[email protected]>:
>> >>>
>> >>> Hi Shino,
>> >>>
>> >>> This behavior is indeed expected.
>> >>>
>> >>> To avoir all registrations to epmd, you can pass the -no_epmd option
>> instead.
>> >>>
>> >>> It is mentioned in the following documentation:
>> >>> https://erlang.org/doc/apps/erts/alt_dist.html
>> >>>
>> >>> Cheers,
>> >>> Jérôme
>> >>>
>> >>> Le ven. 18 déc. 2020 à 03:40, Shunichi Shinohara <
>> [email protected]> a écrit :
>> >>>>
>> >>>> Hi List,
>> >>>>
>> >>>> I try "epmdlessless" configuration described in:
>> >>>>   Running Erlang Releases without EPMD on OTP 23.1+ · Erlware Blog
>> >>>>   https://blog.erlware.org/epmdlessless/
>> >>>>
>> >>>> It works as described, thanks to people who contributed to the
>> feature!
>> >>>> However, it behaves in an unexpected way (to me) under epmd daemon
>> running case.
>> >>>>
>> >>>> Expected behavior is the case without running epmd daemon. After
>> launching a node as:
>> >>>>
>> >>>> % erl -sname foo -start_epmd false -erl_epmd_port 14693
>> >>>> Erlang/OTP 23 [erts-11.1.4] [source] [64-bit] [smp:16:16]
>> [ds:16:16:10] [async-threads:1]
>> >>>>
>> >>>> epmd daemon does *NOT* start, as expected:
>> >>>>
>> >>>> % epmd -names
>> >>>> epmd: Cannot connect to local epmd
>> >>>>
>> >>>> On the other hand, after epmd daemon started as epmd -daemon,
>> >>>> by executing the same erl command above, the node is registered to
>> epmd daemon:
>> >>>>
>> >>>> % epmd -names
>> >>>> epmd: up and running on port 4369 with data:
>> >>>> name foo at port 14693
>> >>>>
>> >>>> The questions are:
>> >>>> - Is this behavior expected (to other than me)?
>> >>>> - Is there any option(s) of erl command to avoid registration to
>> epmd?
>> >>>>   # I guess it's possible by using
>> https://github.com/tsloughter/epmdless
>> >>>>
>> >>>> Thanks,
>> >>>> Shino
>>
>