[erlang-questions] Waiting for a node to start using run_erl

[Garrett Smith]

To measure that specifically then, the two approaches that occur to me
are to either poll the target node from another node by issuing pings,
timing out after a period -- or configuring your target node to ping
back as soon as it starts.

If you don't have another node to control this (which would be odd
given your start definition) you could tail/scan a log file as a proxy
for start state. Or create a sentinel file somewhere that signals the
node is started.

This problem is endemic to coordinating system activity -- it's not
specific to run_erl (even if it blocked, you'd have the same problem
unless it fortuitously exited when you wanted it to).

On Sat, Jun 29, 2013 at 9:48 AM, Yash Ganthe
<yash_ganthe@REDACTED> wrote:
> My definition of "started" is that I am able to PING the node and get a PONG response back.
>
> Thanks,
> Yash
>
> -----Original Message-----
> From: Garrett Smith [mailto:g@REDACTED]
> Sent: Saturday, June 29, 2013 7:43 PM
> To: Yash Ganthe
> Cc: erlang-questions@REDACTED
> Subject: Re: [erlang-questions] Waiting for a node to start using run_erl
>
> What is "started" in this case?
>
> A node start is a system startup, much like an OS start. There should be a point that you system is "ready" to server/act/etc. Once you establish that point, test for for it.
>
> Just as an example of why this isn't always straight forward, consider a socket server (e.g. a web server). You might define "ready" as soon as the server is accepting connections on a port, which is easy to test for. But the server might in fact be ready several seconds later as database connections are opened, caches warmed, whatever. So a ready test might be a 200 response on a particular http request (which is able to test for all those conditions).
>
> On Sat, Jun 29, 2013 at 8:42 AM, Yash Ganthe <yash_ganthe@REDACTED> wrote:
>> Hi,
>>
>>
>>
>> When staring an erl node using run_erl, if the -daemon switch is used,
>> control returns to the terminal immediately without letting me know
>> whether the node was really started.
>>
>> The switch is recommended in the documentation at:
>> http://erlang.org/doc/man/run_erl.html
>>
>>
>>
>> It says: Without this option, run_erl must be started using several
>> tricks in the shell to detach it completely from the terminal in use
>> when starting it.
>>
>>
>>
>> Is there a way to use run_erl and ensure that the node is started.
>> This would be especially useful when starting the node from a shell
>> script using run_erl.
>>
>>
>>
>> Thanks,
>>
>> Yash
>>
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