[role="xpack"]
[[securing-aliases]]
=== Granting privileges for indices and aliases

Elasticsearch allows to execute operations against {ref}/indices-aliases.html[index aliases],
which are effectively virtual indices. An alias points to one or more indices,
holds metadata and potentially a filter. {security} treats aliases and indices
the same. Privileges for indices actions are granted on specific indices or
aliases. In order for an indices action to be authorized, the user that executes
it needs to have permissions for that action on all the specific indices or
aliases that the request relates to.

Let's look at an example. Assuming we have an index called `2015`, an alias that
points to it called `current_year`, and a user with the following role:

[source,js]
--------------------------------------------------
{
  "names" : [ "2015" ],
  "privileges" : [ "read" ]
}
--------------------------------------------------
// NOTCONSOLE

The user attempts to retrieve a document from `current_year`:

[source,shell]
-------------------------------------------------------------------------------
GET /current_year/event/1
-------------------------------------------------------------------------------
// CONSOLE
// TEST[s/^/PUT 2015\n{"aliases": {"current_year": {}}}\nPUT 2015\/event\/1\n{}\n/]

The above request gets rejected, although the user has `read` privilege on the
concrete index that the `current_year` alias points to. The correct permission
would be as follows:

[source,js]
--------------------------------------------------
{
  "names" : [ "current_year" ],
  "privileges" : [ "read" ]
}
--------------------------------------------------
// NOTCONSOLE

[float]
==== Managing aliases

Unlike creating indices, which requires the `create_index` privilege, adding,
removing and retrieving aliases requires the `manage` permission. Aliases can be
added to an index directly as part of the index creation:

[source,shell]
-------------------------------------------------------------------------------
PUT /2015
{
    "aliases" : {
        "current_year" : {}
    }
}
-------------------------------------------------------------------------------
// CONSOLE

or via the dedicated aliases api if the index already exists:

[source,shell]
-------------------------------------------------------------------------------
POST /_aliases
{
    "actions" : [
        { "add" : { "index" : "2015", "alias" : "current_year" } }
    ]
}
-------------------------------------------------------------------------------
// CONSOLE
// TEST[s/^/PUT 2015\n/]

The above requests both require the `manage` privilege on the alias name as well
as the targeted index, as follows:

[source,js]
--------------------------------------------------
{
  "names" : [ "20*", "current_year" ],
  "privileges" : [ "manage" ]
}
--------------------------------------------------
// NOTCONSOLE

The index aliases api also allows also to delete aliases from existing indices.
The privileges required for such a request are the same as above. Both index and
alias need the `manage` permission.


[float]
==== Filtered aliases

Aliases can hold a filter, which allows to select a subset of documents that can
be accessed out of all the documents that the physical index contains. These
filters are not always applied and should not be used in place of
<<document-level-security, document level security>>.