[Hawkular-dev] Fwd: [wildfly-dev] Wildfly start-up as service script depends on console log to determinate start result

[Heiko W.Rupp]

This sounds interesting as it would also be
something like our computed resource state
with some simple form of "alerting" behind it.

Forwarded message:

> From: David M. Lloyd <david.lloyd at redhat.com>
> To: wildfly-dev at lists.jboss.org
> Subject: Re: [wildfly-dev] Wildfly start-up as service script depends 
> on console log to determinate start result
> Date: Fri, 12 Jun 2015 07:57:25 -0500
>
> This is yet another good use case for an idea I proposed at the last
> couple developer meeting: the idea of configurable "availability"
> services, where you add a configuration which says "when these
> components and/or configured services are available, perform this
> action" where the action might be to notify a load balancer, perform a
> notification to humans, or even drop a file to the filesystem (which
> would be directly useful to this use case).
>
> Note (in case someone thinks this is a great idea and runs out to
> implement it right away) that when I say "configured services" I do 
> not
> mean MSC service names; more like management capabilities where you 
> have
> a constrained namespace and each subsystem can contribute services to
> this category.
>
> Also note that Java 9 adds limited support for signalling unrelated
> processes, though at the moment on UNIX the signals are basically
> limited to TERM and KILL.
>
> On 06/12/2015 07:06 AM, Jason T. Greene wrote:
>>
>>> On Jun 10, 2015, at 11:46 AM, Brian Stansberry 
>>> <brian.stansberry at redhat.com> wrote:
>>>
>>> So, what purpose is this fulfilling?
>>>
>>> 2) How does other software solve this problem? If it's solving a 
>>> valid
>>> problem, it seems like there would be a typical solution.
>>
>> The classic UNIX solution is that the daemon forks and returns, 
>> dropping a PID file of its child to disk, after it is done 
>> initializing and exits with an error code when there is a problem.
>>
>> Systemd added other approaches, where a daemon can signal systemd 
>> directly, or it can use dbus to send a message.
>>
>> The former can't be done efficiently in Java because it doesn't have 
>> a pure fork(), only an exec. Although it would be possible to emulate 
>> with an exec with an unacceptable hit to boot time. The latter 
>> options are too Linux specific.
>>
>> I think the best solution would be for us to add a signaling 
>> mechanism specifically for this purpose. We could use sun.misc.Signal 
>> (potentially an issue on Java 9), or we could exec the kill command 
>> to signal a process.
>>
>> We could also use a specially status file (e.g standalone.sh 
>> --start-status-file=blah) for a script to monitor.
>>
>> Thoughts?
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>>
>
> -- 
> - DML
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