ES重建索引

适用于现有索引需要增加一个字段或修改类型

1. 更新模板
   PUT /_template/xxx
2. 建立新索引
   PUT /xxx
3. 重建索引

POST _reindex
{
  "source": {
    "index": "old"
  },
  "dest": {
    "index": "new"
  }}

4. 转移别名

POST /_aliases
{
    "actions": [
        { "remove": { "index": "old", "alias": "xxx" }},
        { "add":    { "index": "new", "alias": "xxx" }}
    ]}