This commit enhances the allocator decision result objects (namely,
AllocateUnassignedDecision, MoveDecision, and RebalanceDecision)
to enable them to be used directly by the cluster allocation explain API. In
particular, this commit does the following:
- Adds serialization and toXContent methods to the response objects,
which will form the explain API responses.
- Moves the calculation of the final explanation to the response
object itself, removing it from the responsibility of the allocators.
- Adds shard store information to the NodeAllocationResult, so that
store information is available for each node, when explaining a
shard allocation by the PrimaryShardAllocator or the ReplicaShardAllocator.
- Removes RebalanceDecision in favor of using MoveDecision for both
moving and rebalancing shards.
- Removes NodeRebalanceResult in favor of using NodeAllocationResult.
- Changes the notion of weight ranking to be relative to the current node,
instead of an absolute weight that doesn't convey any added value to the
API user and can be confusing.
- Introduces a new enum AllocationDecision to convey the decision type,
which enables conveying unassigned, moving, and rebalancing scenarios
with more detail as opposed to just Decision.Type and AllocationStatus.
e6e7bab58c