Re: [Mojolicious] Re: Deployment: launch hypnotoad on boot

[Stefan Adams]

On Thu, Aug 4, 2016 at 8:27 PM, Dan Book  wrote:

> The Watchdog is an optional feature, but if you enable it (with
> WatchdogSec=), the Restart option will include that condition. Otherwise
> the on-failure setting is usually sufficient and will restart it when a
> systemd operation times out or the process exits with a non-zero exit code
> or is terminated by a signal (e.g. SIGKILL, SIGSEGV). As for supporting it
> in Hypnotoad itself, it would be difficult to support via a plugin since
> the manager process (which does not run the IOLoop) would need to be
> sending the notify. And I'm doubtful if such a systemd-specific feature
> would be something the team wants to implement in core.


Great -- thanks again for the insight!  Makes sense about supporting it in
core, but just thought I'd start the conversation about it!  :D

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Re: [Mojolicious] Re: Deployment: launch hypnotoad on boot

[Dan Book]

The Watchdog is an optional feature, but if you enable it (with
WatchdogSec=), the Restart option will include that condition. Otherwise
the on-failure setting is usually sufficient and will restart it when a
systemd operation times out or the process exits with a non-zero exit code
or is terminated by a signal (e.g. SIGKILL, SIGSEGV). As for supporting it
in Hypnotoad itself, it would be difficult to support via a plugin since
the manager process (which does not run the IOLoop) would need to be
sending the notify. And I'm doubtful if such a systemd-specific feature
would be something the team wants to implement in core.

On Thu, Aug 4, 2016 at 8:51 PM, Stefan Adams  wrote:

>
> On Thu, Aug 4, 2016 at 7:41 PM, Dan Book  wrote:
>
>> Systemd has an option for this, see Restart= here
>> https://www.freedesktop.org/software/systemd/man/systemd.service.html
>>
>
> Thanks, Dan!  I understand that a daemon needs to be written to
> specifically handle the watchdog ping.
>
> *Timeouts include missing the watchdog "keep-alive ping" deadline*
>
>
> Do you know if this is necessary or if the other modes are generally
> sufficient to ensure that the service restarts when it fails?
>
> Moreover, would building in watchdog support to hypnotoad be a good idea?
>
> *First of all, to make software watchdog-supervisable it needs to be
> patched to send out "I am alive" signals in regular intervals in its event
> loop. Patching this is relatively easy. First, a daemon needs to read the
> WATCHDOG_USEC= environment variable. If it is set, it will contain the
> watchdog interval in usec formatted as ASCII text string, as it is
> configured for the service. The daemon should then
> issuesd_notify("WATCHDOG=1") calls every half of that interval. A daemon
> patched this way should transparently support watchdog functionality by
> checking whether the environment variable is set and honouring the value it
> is set to.*
>
>
> -- http://0pointer.de/blog/projects/watchdog.html
>
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Re: [Mojolicious] Re: Deployment: launch hypnotoad on boot

[Stefan Adams]

On Thu, Aug 4, 2016 at 7:41 PM, Dan Book  wrote:

> Systemd has an option for this, see Restart= here https://www.freedesktop.
> org/software/systemd/man/systemd.service.html
>

Thanks, Dan!  I understand that a daemon needs to be written to
specifically handle the watchdog ping.

*Timeouts include missing the watchdog "keep-alive ping" deadline*


Do you know if this is necessary or if the other modes are generally
sufficient to ensure that the service restarts when it fails?

Moreover, would building in watchdog support to hypnotoad be a good idea?

*First of all, to make software watchdog-supervisable it needs to be
patched to send out "I am alive" signals in regular intervals in its event
loop. Patching this is relatively easy. First, a daemon needs to read the
WATCHDOG_USEC= environment variable. If it is set, it will contain the
watchdog interval in usec formatted as ASCII text string, as it is
configured for the service. The daemon should then
issuesd_notify("WATCHDOG=1") calls every half of that interval. A daemon
patched this way should transparently support watchdog functionality by
checking whether the environment variable is set and honouring the value it
is set to.*


-- http://0pointer.de/blog/projects/watchdog.html

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Re: [Mojolicious] Re: Deployment: launch hypnotoad on boot

[Dan Book]

Systemd has an option for this, see Restart= here
https://www.freedesktop.org/software/systemd/man/systemd.service.html

On Thu, Aug 4, 2016 at 7:42 PM, Stefan Adams  wrote:

> I've noticed that sometimes my hypnotoad just dies, no warning.  Is there
> a supported directive for systemd to allow systemd to auto-restart the
> service if the process hangs or disappears?
>
> On Sat, Jul 30, 2016 at 4:15 PM, sri  wrote:
>
>> Mojolicious 7.01 will have better systemd support and we'll add unit file
>> examples to the docs.
>>
>> https://github.com/kraih/mojo/compare/d87c59fc0fa1c4450d59
>> 5fc7b3bbdd24faf64e7a...7299bf4442b09ee8451953aba99f97abe9864
>> 7bf#diff-b659d9bfeffa6b78a1f2950c7e72259bR151
>>
>
>
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Re: [Mojolicious] Re: Deployment: launch hypnotoad on boot

[Stefan Adams]

I've noticed that sometimes my hypnotoad just dies, no warning.  Is there a
supported directive for systemd to allow systemd to auto-restart the
service if the process hangs or disappears?

On Sat, Jul 30, 2016 at 4:15 PM, sri  wrote:

> Mojolicious 7.01 will have better systemd support and we'll add unit file
> examples to the docs.
>
> https://github.com/kraih/mojo/compare/d87c59fc0fa1c4450d595fc7b3bbdd
> 24faf64e7a...7299bf4442b09ee8451953aba99f97abe98647bf#diff-
> b659d9bfeffa6b78a1f2950c7e72259bR151
>

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