elasticsearch 产生未分配分片的原因（es官网）

Reasons for unassigned shard：

These are the possible reasons for a shard to be in a unassigned state:

1. INDEX_CREATED    Unassigned as a result of an API creation of an index.    索引创建  由于API创建索引而未分配的

2. CLUSTER_RECOVERED    Unassigned as a result of a full cluster recovery.   集群恢复   由于整个集群恢复而未分配

3. INDEX_REOPENED    Unassigned as a result of opening a closed index.        索引重新打开   

4. DANGLING_INDEX_IMPORTED    Unassigned as a result of importing a dangling index.   导入危险的索引

5. NEW_INDEX_RESTORED     Unassigned as a result of restoring into a new index.   重新恢复一个新索引

6. EXISTING_INDEX_RESTORED    Unassigned as a result of restoring into a closed index.  重新恢复一个已关闭的索引

7. REPLICA_ADDED     Unassigned as a result of explicit addition of a replica.      添加副本

8. ALLOCATION_FAILED    Unassigned as a result of a failed allocation of the shard.    分配分片失败

9. NODE_LEFT     Unassigned as a result of the node hosting it leaving the cluster.  集群中节点丢失

10. REROUTE_CANCELLED     Unassigned as a result of explicit cancel reroute command.   reroute命令取消

11. REINITIALIZED     When a shard moves from started back to initializing, for example, with shadow replicas.   重新初始化

12. REALLOCATED_REPLICA       A better replica location is identified and causes the existing replica allocation to be cancelled.   重新分配副本