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

[Rob Crittenden]

Nathan Kinder wrote:
> 
> 
> 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
> 

LGTM. Does someone else have time to test this?

I also don't know if there is a policy on placement of new items in
paths.py. Things are all over the place and some have BIN_ prefix and
some don't.

rob