# Why can index alias index routing only contain a single value?

**URL:** <https://discuss.elastic.co/t/why-can-index-alias-index-routing-only-contain-a-single-value/365>\
**Category:** Elasticsearch\
**Created:** [May 7, 2015, 11:53pm UTC](https://discuss.elastic.co/t/why-can-index-alias-index-routing-only-contain-a-single-value/365 "2015-05-07T23:53:36Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bjfish](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/bjfish/32/32676_2.png) [@bjfish](https://discuss.elastic.co/u/bjfish)\
**Post date:** [May 7, 2015, 11:53pm UTC](https://discuss.elastic.co/t/why-can-index-alias-index-routing-only-contain-a-single-value/365/1 "2015-05-07T23:53:36Z")

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Why can index alias index routing only contain a single value?

The guide mentions "Index routing can contain only a single value." [http://www.elastic.co/guide/en/elasticsearch/reference/current/indices-aliases.html](http://www.elastic.co/guide/en/elasticsearch/reference/current/indices-aliases.html)

It seems like it would be useful to index into multiple indexes at once so I am wondering why this isn't available.

Thank you.

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**Author:** ![jaddison](https://avatars.discourse-cdn.com/v4/letter/j/e5b9ba/32.png) [@jaddison](https://discuss.elastic.co/u/jaddison)\
**Post date:** [May 8, 2015, 10:49pm UTC](https://discuss.elastic.co/t/why-can-index-alias-index-routing-only-contain-a-single-value/365/2 "2015-05-08T22:49:30Z")

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Routing is all about manipulating operations at the shard level, not index level. You can only add a document to a single shard within an index.

You can search multiple shards of course, which is why multiple routing values are permitted there. From the docs:

> **Routing**

> It is possible to associate routing values with aliases. This feature can be used together with filtering aliases in order to _ **avoid unnecessary shard operations** _.

> It’s also possible to specify different routing values for searching and indexing operations:

```
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        {
            "add" : {
                 "index" : "test",
                 "alias" : "alias2",
                 "search_routing" : "1,2",
                 "index_routing" : "2"
            }
        }
    ]
}'

```

> As shown in the example above, _ **search routing may contain several values** _ separated by comma. Index routing can contain only a single value.

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 6, 2017, 12:14am UTC](https://discuss.elastic.co/t/why-can-index-alias-index-routing-only-contain-a-single-value/365/3 "2017-07-06T00:14:55Z")

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Closed on July 6, 2017, 12:14am UTC