70_Faking_it.asciidoc

Faking Index per User with Aliases

To keep our design simple and clean, we would like our application to believe that we have a dedicated index per user—​or per forum in our example—​even if the reality is that we are using one big shared index. To do that, we need some way to hide the routing value and the filter on forum_id.

Index aliases allow us to do just that. When you associate an alias with an index, you can also specify a filter and routing values:

PUT /forums/_alias/baking
{
  "routing": "baking",
  "filter": {
    "term": {
      "forum_id": "baking"
    }
  }
}

Now, we can treat the baking alias as if it were its own index. Documents indexed into the baking alias automatically get the custom routing value applied:

PUT /baking/post/1 (1)
{
  "forum_id": "baking", (1)
  "title":    "Easy recipe for ginger nuts",
  ...
}

1. We still need the forum_id field for the filter to work, but the custom routing value is now implicit.

Queries run against the baking alias are run just on the shard associated with the custom routing value, and the results are automatically filtered by the filter we specified:

GET /baking/post/_search
{
  "query": {
    "match": {
      "title": "ginger nuts"
    }
  }
}

Multiple aliases can be specified when searching across multiple forums:

GET /baking,recipes/post/_search (1)
{
  "query": {
    "match": {
      "title": "ginger nuts"
    }
  }
}

1. Both routing values are applied, and results can match either filter.