opensearch-docs-cn/_im-plugin/index-alias.md

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---
layout: default
title: Index aliases
nav_order: 11
redirect_from:
- /opensearch/index-alias/
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---
# Index aliases
An alias is a virtual index name that can point to one or more indexes.
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If your data is spread across multiple indexes, rather than keeping track of which indexes to query, you can create an alias and query it instead.
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For example, if youre storing logs into indexes based on the month and you frequently query the logs for the previous two months, you can create a `last_2_months` alias and update the indexes it points to each month.
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Because you can change the indexes an alias points to at any time, referring to indexes using aliases in your applications allows you to reindex your data without any downtime.
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---
#### Table of contents
1. TOC
{:toc}
---
## Create aliases
To create an alias, use a POST request:
```json
POST _aliases
```
Use the `actions` method to specify the list of actions that you want to perform. This command creates an alias named `alias1` and adds `index-1` to this alias:
```json
POST _aliases
{
"actions": [
{
"add": {
"index": "index-1",
"alias": "alias1"
}
}
]
}
```
You should see the following response:
```json
{
"acknowledged": true
}
```
If this request fails, make sure the index that you're adding to the alias already exists.
You can also create an alias using one of the following requests:
```json
PUT <index>/_aliases/<alias name>
PUT <index>/_aliases/<alias name>
POST <index>/_alias/<alias name>
POST <index>/_alias/<alias name>
```
The `<index>` in the above requests can be an index name, a comma-separated list of index names, or a wildcard expression. Use `_all` to refer to all indexes.
To check if `alias1` refers to `index-1`, run one of the following commands:
```json
GET /_alias/alias1
GET /index-1/_alias/alias1
```
To get the mappings and settings information of the indexes that the alias references, run the following command:
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```json
GET alias1
```
## Add or remove indexes
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You can perform multiple actions in the same `_aliases` operation.
For example, the following command removes `index-1` and adds `index-2` to `alias1`:
```json
POST _aliases
{
"actions": [
{
"remove": {
"index": "index-1",
"alias": "alias1"
}
},
{
"add": {
"index": "index-2",
"alias": "alias1"
}
}
]
}
```
The `add` and `remove` actions occur atomically, which means that at no point will `alias1` point to both `index-1` and `index-2`.
You can also add indexes based on an index pattern:
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```json
POST _aliases
{
"actions": [
{
"add": {
"index": "index*",
"alias": "alias1"
}
}
]
}
```
## Manage aliases
To list the mapping of aliases to indexes, run the following command:
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```json
GET _cat/aliases?v
```
#### Example response
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```json
alias index filter routing.index routing.search
alias1 index-1 * - -
```
To check which indexes an alias points to, run the following command:
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```json
GET _alias/alias1
```
#### Example response
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```json
{
"index-2": {
"aliases": {
"alias1": {}
}
}
}
```
Conversely, to find which alias points to a specific index, run the following command:
```json
GET /index-2/_alias/*
```
To get all index names and their aliases, run the following command:
```json
GET /_alias
```
To check if an alias exists, run one of the following commands:
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```json
HEAD /alias1/_alias/
HEAD /_alias/alias1/
HEAD index-1/_alias/alias1/
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```
## Add aliases at index creation
You can add an index to an alias as you create the index:
```json
PUT index-1
{
"aliases": {
"alias1": {}
}
}
```
## Create filtered aliases
You can create a filtered alias to access a subset of documents or fields from the underlying indexes.
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This command adds only a specific timestamp field to `alias1`:
```json
POST _aliases
{
"actions": [
{
"add": {
"index": "index-1",
"alias": "alias1",
"filter": {
"term": {
"timestamp": "1574641891142"
}
}
}
}
]
}
```
## Index alias options
You can specify the options shown in the following table.
Option | Valid values | Description | Required
:--- | :--- | :---
`index` | String | The name of the index that the alias points to. | Yes
`alias` | String | The name of the alias. | No
`filter` | Object | Add a filter to the alias. | No
`routing` | String | Limit search to an associated shard value. You can specify `search_routing` and `index_routing` independently. | No
`is_write_index` | String | Specify the index that accepts any write operations to the alias. If this value is not specified, then no write operations are allowed. | No
## Delete aliases
To delete one or more aliases from an index, use the following request:
```json
DELETE <index>/_alias/<alias>
DELETE <index>/_aliases/<alias>
```
Both `<index>` and `<alias>` in the above request support comma-separated lists and wildcard expressions. Use `_all` in place of `<alias>` to delete all aliases for the indexes listed in `<index>`.
For example, if `alias1` refers to `index-1` and `index-2`, you can run the following command to remove `alias1` from `index-1`:
```json
DELETE index-1/_alias/alias1
```
After you run the request above, `alias1` no longer refers to `index-1`, but still refers to `index-2`.