[Freeipa-devel] [PATCHES 0001-0002] ipa-client-install NTP fixes

[Nathan Kinder]

On 02/28/2015 01:13 PM, Nathan Kinder wrote:
> 
> 
> 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.

Another updated patch 0002 is attached that addresses Rob's review comments.

Thanks,
-NGK

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