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From Andy Kurth <andy_ku...@ncsu.edu>
Subject Re: frontend API for block reservations (VCL-78)
Date Thu, 05 Feb 2009 16:20:54 GMT
This is just semantics for now but it might be better to think of the number of 
things being allocated as requests rather than machines.  This will allow for 
block requests of cluster images.

Regarding the return code... it might be useful to return the number of requests 
that haven't been successfully allocated for the block time.  A return code of 0 
would mean all of the resources for the block time have been successfully allocated.

The backend wouldn't need to worry about the total number of requests that are 
needed nor would it care how many were successfully allocated during this stage. 
  It would only have to know if the number which couldn't be allocated is 
greater than 0.

This would make it easy to add some failure recovery features in the future.  If 
the number which hasn't yet been allocated is greater than 0, the backend 
process could make multiple attempts by sleeping and looping.

-Andy



Josh Thompson wrote:
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> For the frontend, one function works as well as two would.  However, I can see 
> how it would simplify code on the backend to just pass a blockTimes id since 
> it wouldn't have to determine all of the other information (blockTimes 
> entries include blockrequestids; so, the blockrequestid wouldn't need to be 
> passed as well).
> 
> So, how about this, keep the function already described except drop 
> the 'blockTimeid' parameter and add this function as well:
> 
> function: XMLRPCproccessBlockTime
> 
> parameters:
>   blockTimesid - id from the blockTimes table
>   ignoreprivileges - 0 (false) or 1 (true) - set to 1 to select computers from  
> any that are mapped to be able to run the image; set to 0 to only select  
> computers from ones that are both mapped and that users in the usergroup 
> assigned to this block request have been granted access to through the 
> privilege tree.
> 
> returns: the number of machines that were successfully allocated, with 0
> indicating a complete failure of not being able to allocate any computers
> 
> 
> I just realized a problem in the return part of both functions.  What if the 
> function is called too close to the start time to be able to preload the 
> computers by then?  Should it just return 0 and not try to load any of them?  
> It may be that the functions need to return an array containing both a return 
> code and the number of computers that were successfully allocated.  Thoughts?
> 
> Josh
> 
> On Thursday February 05, 2009, Aaron Peeler wrote:
>> Would it make sense to break this into two functions?
>>
>> Have this function XMLRPCblockAllocation with only two parameters
>> blockrequestid and blockTimeid.
>>
>> The second function would be to create the Block Allocation -
>> XMLRPCcreateBlockAllocation.
>>
>> Aaron
>>
>> --On February 4, 2009 4:39:30 PM -0500 Josh Thompson
>>
>> <josh_thompson@ncsu.edu> wrote:
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>>> I'm going to start work on VCL-78 which is an addition to the frontend
>>> XML RPC  API to allow the backend to call the frontend for allocating
>>> computers for  block reservations.  Currently, the block reservations are
>>> created in the  frontend, but computers are not allocated to fulfill them
>>> because the  requested time(s) could be at any point in the future.  So,
>>> around 6 hours  before a requested time, the backend picks up that block
>>> reservation time  slot, allocates computers for it, and then inserts
>>> reload reservations early  enough for the computers to be preloaded by
>>> the start of the time slot.
>>>
>>> This results in a fair amount of duplicated code, since the frontend
>>> currently  handles computer allocation in all other cases.
>>>
>>> This is how I am planning on implementing it.  Please reply with any
>>> comments  on doing it differently or tweaking it somehow.  I'm open to
>>> any suggestions.
>>>
>>> The backend could just call the frontend with the blockTimes id to
>>> process,  but I'll make it more generic to be more useful in other cases
>>> and require  that the backend specify several items.
>>>
>>> function name: XMLRPCblockAllocation
>>>
>>> parameters:
>>>   imageid - id of the image to be used
>>>   start - unix timestamp for the start time (i.e. machines should be
>>> prep'd  and ready by this time)
>>>   end - unix timestamp for the end time
>>>   machinecount - number of computers to allocate
>>>   usergroupid - id of user group for checking user access to machines
>>>   ignoreprivileges - 0 (false) or 1 (true) - set to 1 to select computers
>>> from  any that are mapped to be able to run the image; set to 0 to only
>>> select  computers from ones that are both mapped and that users in
>>> usergroupid have  been granted access to through the privilege tree.  If
>>> this is set to 1,  usergroupid is ignored (more on this below).
>>>   blockTimeid - id from blockTimes table that this will fulfill or 0 if
>>> there  is not an existing block reservation related to this call
>>>
>>> returns: the number of machines that were successfully allocated, with 0
>>> indicating a complete failure of not being able to allocate any computers
>>>
>>> Description of how it will work:
>>> The frontend will use the normal scheduling functions to allocate
>>> computers  and insert them into the blockComputers table.  If blockTimeid
>>> is 0, new  entries will be created in the blockRequest and blockTimes
>>> tables.  It will  create reload reservations for the computers early
>>> enough for them to be  loaded by the start time based on historical
>>> loading times.
>>>
>>> The ignoreprivileges flag exists to allow more machines to be available
>>> for  fulfilling block reservations than just those that the user group
>>> has access  to.  The current implementation with the backend doing the
>>> processing  functions as if ignoreprivileges were set to 1.
>>>
>>> That's pretty much it.
>>>
>>> Josh
>>> - --
>>> - -------------------------------
>>> Josh Thompson
>>> Systems Programmer
>>> Virtual Computing Lab (VCL)
>>> North Carolina State University
>>>
>>> Josh_Thompson@ncsu.edu
>>> 919-515-5323
>>>
>>> my GPG/PGP key can be found at pgp.mit.edu
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>>> NK5Mjyap5+oeemdm40DEdaQ=
>>> =e3CH
>>> -----END PGP SIGNATURE-----
>> Aaron Peeler
>> OIT Advanced Computing
>> College of Engineering-NCSU
>> 919.513.4571
>> http://vcl.ncsu.edu
> 
> 
> 
> - -- 
> - -------------------------------
> Josh Thompson
> Systems Programmer
> Virtual Computing Lab (VCL)
> North Carolina State University
> 
> Josh_Thompson@ncsu.edu
> 919-515-5323
> 
> my GPG/PGP key can be found at pgp.mit.edu
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> Vxd5BgeBEphBMu+RSbSIw84=
> =09dV
> -----END PGP SIGNATURE-----

-- 
Andy Kurth
Virtual Computing Lab
Office of Information Technology
North Carolina State University
andy_kurth@ncsu.edu
919.513.4090


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