On 02/28/2015 01:07 PM, Rob Crittenden wrote:
> Nathan Kinder wrote:
>> On 02/27/2015 01:18 PM, Nathan Kinder wrote:
>>> On 02/27/2015 01:08 PM, Rob Crittenden wrote:
>>>> Nathan Kinder wrote:
>>>>> On 02/27/2015 12:20 PM, Rob Crittenden wrote:
>>>>>> Nathan Kinder wrote:
>>>>>>> On 02/26/2015 12:55 AM, Martin Kosek wrote:
>>>>>>>> On 02/26/2015 03:28 AM, Nathan Kinder wrote:
>>>>>>>>> Hi,
>>>>>>>>> The two attached patches address some issues that affect
>>>>>>>>> ipa-client-install when syncing time from the NTP server.  Now that we
>>>>>>>>> use ntpd to perform the time sync, the client install can end up 
>>>>>>>>> hanging
>>>>>>>>> forever when the server is not reachable (firewall issues, etc.).  
>>>>>>>>> These
>>>>>>>>> patches address the issues in two different ways:
>>>>>>>>> 1 - Don't attempt to sync time when --no-ntp is specified.
>>>>>>>>> 2 - Implement a timeout capability that is used when we run ntpd to
>>>>>>>>> perform the time sync to prevent indefinite hanging.
>>>>>>>>> The one potentially contentious issue is that this introduces a new
>>>>>>>>> dependency on python-subprocess32 to allow us to have timeout support
>>>>>>>>> when using Python 2.x.  This is packaged for Fedora, but I don't see 
>>>>>>>>> it
>>>>>>>>> on RHEL or CentOS currently.  It would need to be packaged there.
>>>>>>>>> https://fedorahosted.org/freeipa/ticket/4842
>>>>>>>>> Thanks,
>>>>>>>>> -NGK
>>>>>>>> Thanks for Patches. For the second patch, I would really prefer to 
>>>>>>>> avoid new
>>>>>>>> dependency, especially if it's not packaged in RHEL/CentOS. Maybe we 
>>>>>>>> could use
>>>>>>>> some workaround instead, as in:
>>>>>>>> http://stackoverflow.com/questions/3733270/python-subprocess-timeout
>>>>>>> I don't like having to add an additional dependency either, but the
>>>>>>> alternative seems more risky.  Utilizing the subprocess32 module (which
>>>>>>> is really just a backport of the normal subprocess module from Python
>>>>>>> 3.x) is not invasive for our code in ipautil.run().  Adding some sort of
>>>>>>> a thread that has to kill the spawned subprocess seems more risky (see
>>>>>>> the discussion about a race condition in the stackoverflow thread
>>>>>>> above).  That said, I'm sure the thread/poll method can be made to work
>>>>>>> if you and others feel strongly that this is a better approach than
>>>>>>> adding a new dependency.
>>>>>> Why not use /usr/bin/timeout from coreutils?
>>>>> That sounds like a perfectly good idea.  I wasn't aware of it's
>>>>> existence (or it's possible that I forgot about it).  Thanks for the
>>>>> suggestion!  I'll test out a reworked version of the patch.
>>>>> Do you think that there is value in leaving the timeout capability
>>>>> centrally in ipautil.run()?  We only need it for the call to 'ntpd'
>>>>> right now, but there might be a need for using a timeout for other
>>>>> commands in the future.  The alternative is to just modify
>>>>> synconce_ntp() to use /usr/bin/timeout and leave ipautil.run() alone.
>>>> I think it would require a lot of research. One of the programs spawned
>>>> by this is pkicreate which could take quite some time, and spawning a
>>>> clone in particular.
>>>> It is definitely an interesting idea but I think it is safest for now to
>>>> limit it to just NTP for now.
>>> What I meant was that we would have an optional keyword "timeout"
>>> parameter to ipautil.run() that defaults to None, just like my
>>> subprocess32 approach.  If a timeout is not passed in, we would use
>>> subprocess.Popen() to run the specified command just like we do today.
>>> We would only actually pass the timeout parameter to ipautil.run() in
>>> synconce_ntp() for now, so no other commands would have a timeout in
>>> effect.  The capability would be available for other commands this way
>>> though.
>>> Let me propose a patch with this implementation, and if you don't like
>>> it, we can leave ipautil.run() alone and restrict the changes to
>>> synconce_ntp().
>> An updated patch 0002 is attached that uses the approach mentioned above.
> Looks good. Not to nitpick to death but...
> Can you add timeout to ipaplatform/base/paths.py as BIN_TIMEOUT =
> "/usr/bin/timeout" and reference that instead? It's for portability.

Sure.  I was wondering if we should do something around a full path.

> And a question. I'm impatient. Should there be a notice that it will
> timeout after n seconds somewhere so people like me don't ^C after 2
> seconds? Or is that just overkill and I need to learn patience?

Probably both. :)  There's always going to be someone out there who will
do ctrl-C, so I think printing out a notice is a good idea.  I'll add this.

> Stylistically, should we prefer p.returncode is 15 or p.returncode == 15?

After some reading, it seems that '==' should be used.  Small integers
work with 'is', but '==' is the consistent way that equality of integers
should be checked.  I'll modify this.


> rob

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