一、索引分片分配简介：
1、索引恢复速度，并发控制
cluster.routing.allocation.enabled:true。
cluster.routing.allocation.node_concurrent_incoming_recoveries:2
cluster.routing.allocation.node_concurrent_outing_recoveries:2
cluster.routing.allocation.node_concurrent_recoveries:2
cluster.routing.allocation.node_initial_primaries_recoveries:4
cluster.routing.allocation.same_shard.host:false
cluster.routing.rebalance.enabled:all/primaries/replicas/none
cluster.routing.allocation.all_balance:all/primaries/replicas/none
cluster.routing.allocation.cluster_concurrent_rebalance:2
2、磁盘水位，85%：不再分配节点，90%：迁出节点，95%。
cluster.routing.allocation.disk.watermark.low:85%
cluster.routing.allocation.disk.watermark.high:90%
3、机架感知
cluster.routing.allocation.awareness.attributes:zone
node.attr.zone=zone_one
cluster.routing.allocation.awareness.force.zone.values:zone_one,zone_two
4、索引分片分配过滤
cluster.routing.allocation.require/include/execute.{attribute}
attribute:_name,_ip,_tier
5、延时分配
index.unassigned.node_left.delayed_timeout
