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From "Michael Park" <>
Subject Re: Review Request 35702: Added /reserve HTTP endpoint to the master.
Date Wed, 05 Aug 2015 19:12:23 GMT

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(Updated Aug. 5, 2015, 7:12 p.m.)

Review request for mesos, Adam B, Benjamin Hindman, Ben Mahler, Jie Yu, Joris Van Remoortere,
and Vinod Kone.


Removed `Nothing`

Bugs: MESOS-2600

Repository: mesos

Description (updated)

This involved a lot more challenges than I anticipated, I've captured the various approaches
and limitations and deal-breakers of those approaches here: [Master Endpoint Implementation

Key points:

* This is a stop-gap solution until we shift the offer creation/management logic from the
master to the allocator.
* `updateAvailable` and `updateSlave` are kept separate because
  (1) `updateAvailable` is allowed to fail whereas `updateSlave` must not.
  (2) `updateAvailable` returns a `Future` whereas `updateSlave` does not.
  (3) `updateAvailable` never leaves the allocator in an over-allocated state and must not,
whereas `updateSlave` does, and can.
* The algorithm:
    * Initially, the master pessimistically assume that what seems like "available" resources
will be gone.
      This is due to the race between the allocator scheduling an `allocate` call to itself
vs master's
      `allocator->updateAvailable` invocation.
      As such, we first try to satisfy the request only with the offered resources.
    * We greedily rescind one offer at a time until we've rescinded sufficiently many offers.
      IMPORTANT: We perform `recoverResources(..., Filters())` which has a default `refuse_sec`
of 5 seconds,
      rather than `recoverResources(..., None())` so that we can virtually always win the
race against `allocate`.
      In the rare case that we do lose, no disaster occurs. We simply fail to satisfy the
    * If we still don't have enough resources after resciding all offers, be semi-optimistic
and forward the
      request to the allocator since there may be available resources to satisfy the request.
    * If the allocator returns a failure, report the error to the user with `Conflict`.

This approach is clearly not ideal, since we would prefer to rescind as little offers as possible.

Diffs (updated)

  src/master/http.cpp 76e70801925041f08bc94f0ca18c86f1a573b2b3 
  src/master/master.hpp e44174976aa64176916827bec4c911333c9a91db 
  src/master/master.cpp 50b98248463fc4cd48962890c14c7ad64f2b6f43 
  src/master/validation.hpp 43b8d84556e7f0a891dddf6185bbce7ca50b360a 
  src/master/validation.cpp ffb7bf07b8a40d6e14f922eabcf46045462498b5 



`make check`


Michael Park

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