[[securing-aliases]]
=== Granting Privileges for Indices & 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.
Shield 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 by Shield, 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,yaml]
--------------------------------------------------
current_year_read:
  indices:
    '2015': read
--------------------------------------------------

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

[source,shell]
-------------------------------------------------------------------------------
curl -XGET 'localhost:9200/current_year/logs/1'
-------------------------------------------------------------------------------

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

[source,yaml]
--------------------------------------------------
current_year_read:
  indices:
    'current_year': read
--------------------------------------------------

[float]
==== Managing aliases

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

[source,shell]
-------------------------------------------------------------------------------
curl -XPUT localhost:9200/2015 -d '{
    "aliases" : {
        "current_year" : {}
    }
}'
-------------------------------------------------------------------------------

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

[source,shell]
-------------------------------------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "add" : { "index" : "2015", "alias" : "current_year" } }
    ]
}'
-------------------------------------------------------------------------------

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

[source,yaml]
--------------------------------------------------
admin:
  indices:
    '20*,current_year': create_index,manage_aliases
--------------------------------------------------

Note also that the `manage` privilege includes both `create_index` and `manage_aliases` in addition to all of the other
management related privileges:

[source,yaml]
--------------------------------------------------
admin:
  indices:
    '20*,current_year': manage
--------------------------------------------------

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

[source,shell]
-------------------------------------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "delete" : { "index" : "2015", "alias" : "current_year" } }
    ]
}'
-------------------------------------------------------------------------------

[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>>.
