一 read_only_allow_delete" : "true"

当我们在向某个索引添加一条数据的时候，可能（极少情况）会碰到下面的报错：

{"error": {   "root_cause": [     {       "type": "cluster_block_exception",       "reason": "blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];"     }   ],   "type": "cluster_block_exception",   "reason": "blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];"},"status": 403
}

上述报错是说索引现在的状态是只读模式（read-only），如果查看该索引此时的状态：

GET z1/_settings
# 结果如下
{"z1" : {   "settings" : {     "index" : {       "number_of_shards" : "5",       "blocks" : {         "read_only_allow_delete" : "true"       },       "provided_name" : "z1",       "creation_date" : "1556204559161",       "number_of_replicas" : "1",       "uuid" : "3PEevS9xSm-r3tw54p0o9w",       "version" : {         "created" : "6050499"       }     }   }}
}

可以看到"read_only_allow_delete" : "true"，说明此时无法插入数据，当然，我们也可以模拟出来这个错误：

PUT z1
{"mappings": {   "doc": {     "properties":