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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
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Josh Thompson
Systems Programmer
Virtual Computing Lab (VCL)
North Carolina State University

josh_thomp...@ncsu.edu
919-515-5323

my GPG/PGP key can be found at pgp.mit.edu
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