To integrate with Active Directory, you configure an `active_directory`
realm and map Active Directory users and groups to roles in the role mapping file.

. Add a realm configuration of type `active_directory` to `elasticsearch.yml`
under the `xpack.security.authc.realms.active_directory` namespace.
At a minimum, you must specify the Active Directory `domain_name`.
If you are configuring multiple realms, you should also 
explicitly set the `order` attribute to control the order in which the realms 
are consulted during authentication. 
+
--
See <<ref-ad-settings>> for all of the options you can set for an 
`active_directory` realm.

NOTE: Binding to Active Directory fails if the domain name is not mapped in DNS.
      If DNS is not being provided by a Windows DNS server, add a mapping for
      the domain in the local `/etc/hosts` file.

For example, the following realm configuration configures {es} to connect
to `ldaps://example.com:636` to authenticate users through Active Directory:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        active_directory:
          my_ad:
            order: 0 <1>
            domain_name: ad.example.com
            url: ldaps://ad.example.com:636 <2>
------------------------------------------------------------
<1> The realm order controls the order in which the configured realms are checked
    when authenticating a user.
<2> If you don't specify the URL, it defaults to `ldap:<domain_name>:389`.

IMPORTANT: When you configure realms in `elasticsearch.yml`, only the
realms you specify are used for authentication. If you also want to use the
`native` or `file` realms, you must include them in the realm chain.
--

. If you are authenticating users across multiple domains in a forest, extra 
steps are required. There are a few minor differences in the configuration and 
the way that users authenticate. 
+
--
Set the `domain_name` setting to the forest root domain name. 

You must also set the `url` setting, since you must authenticate against the 
Global Catalog, which uses a different port and might not be running on every 
Domain Controller.

For example, the following realm configuration configures {es} to connect 
to specific Domain Controllers on the Global Catalog port with the domain name 
set to the forest root:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        active_directory:
          my_ad:
            order: 0
            domain_name: example.com <1>
            url: ldaps://dc1.ad.example.com:3269, ldaps://dc2.ad.example.com:3269 <2>
            load_balance:
              type: "round_robin" <3>
------------------------------------------------------------
<1> The `domain_name` is set to the name of the root domain in the forest.
<2> The `url` value used in this example has URLs for two different Domain Controllers,
which are also Global Catalog servers. Port 3268 is the default port for unencrypted
communication with the Global Catalog; port 3269 is the default port for SSL connections.
The servers that are being connected to can be in any domain of the forest as long as
they are also Global Catalog servers.
<3> A load balancing setting is provided to indicate the desired behavior when choosing
the server to connect to.

In this configuration, users will need to use either their full User Principal
Name (UPN) or their Down-Level Logon Name. A UPN is typically a concatenation of
the username with `@<DOMAIN_NAME` such as `johndoe@ad.example.com`. The Down-Level
Logon Name is the NetBIOS domain name, followed by a `\` and the username, such as
`AD\johndoe`. Use of Down-Level Logon Name requires a connection to the regular LDAP
ports (389 or 636) in order to query the configuration container to retrieve the
domain name from the NetBIOS name.
--

. (Optional) Configure how {es} should interact with multiple Active 
Directory servers. 
+ 
--
The `load_balance.type` setting can be used at the realm level. Two modes of
operation are supported: failover and load balancing. See <<ref-ad-settings>>. 
--

. (Optional) To protect passwords, 
<<tls-active-directory,encrypt communications between {es} and the Active Directory server>>. 

. Restart {es}.

. (Optional) Configure a bind user. 
+
--
The Active Directory realm authenticates users using an LDAP bind request. By 
default, all of the LDAP operations are run by the user that {es} is
authenticating. In some cases, regular users may not be able to access all of the
necessary items within Active Directory and a _bind user_ is needed. A bind user
can be configured and is used to perform all operations other than the LDAP bind 
request, which is required to authenticate the credentials provided by the user.

The use of a bind user enables the 
<<run-as-privilege,run as feature>> to be used with the Active 
Directory realm and the ability to maintain a set of pooled connections to 
Active Directory. These pooled connection reduce the number of resources that 
must be created and destroyed with every user authentication.

The following example shows the configuration of a bind user through the user of 
the `bind_dn` and `secure_bind_password` settings:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        active_directory:
          my_ad:
            order: 0
            domain_name: ad.example.com
            url: ldaps://ad.example.com:636
            bind_dn: es_svc_user@ad.example.com <1>
------------------------------------------------------------
<1> This is the user that all Active Directory search requests are executed as.
    Without a bind user configured, all requests run as the user that is authenticating
    with {es}.

The password for the `bind_dn` user should be configured by adding the 
appropriate `secure_bind_password` setting to the {es} keystore. For example, 
the following command adds the password for the example realm above:

[source, shell]
------------------------------------------------------------
bin/elasticsearch-keystore add  \
xpack.security.authc.realms.active_directory.my_ad.secure_bind_password
------------------------------------------------------------

When a bind user is configured, connection pooling is enabled by default.
Connection pooling can be disabled using the `user_search.pool.enabled` setting.
--

. Map Active Directory users and groups to roles. 
+
--
An integral part of a realm authentication process is to resolve the roles
associated with the authenticated user. Roles define the privileges a user has
in the cluster.

Since with the `active_directory` realm the users are managed externally in the
Active Directory server, the expectation is that their roles are managed there
as well. In fact, Active Directory supports the notion of groups, which often
represent user roles for different systems in the organization.

The `active_directory` realm enables you to map Active Directory users to roles
via their Active Directory groups or other metadata. This role mapping can be
configured via the <<security-role-mapping-apis,role-mapping APIs>> or by using
a file stored on each node. When a user authenticates against an Active
Directory realm, the privileges for that user are the union of all privileges
defined by the roles to which the user is mapped.

Within a mapping definition, you specify groups using their distinguished
names. For example, the following mapping configuration maps the Active
Directory `admins` group to both the `monitoring` and `user` roles, maps the
`users` group to the `user` role and maps the `John Doe` user to the `user`
role.

Configured via the role-mapping API:

[source,console]
--------------------------------------------------
PUT /_security/role_mapping/admins
{
  "roles" : [ "monitoring" , "user" ],
  "rules" : { "field" : {
    "groups" : "cn=admins,dc=example,dc=com" <1>
  } },
  "enabled": true
}
--------------------------------------------------

<1> The Active Directory distinguished name (DN) of the `admins` group.

[source,console]
--------------------------------------------------
PUT /_security/role_mapping/basic_users
{
  "roles" : [ "user" ],
  "rules" : { "any": [
    { "field" : {
      "groups" : "cn=users,dc=example,dc=com" <1>
    } },
    { "field" : {
      "dn" : "cn=John Doe,cn=contractors,dc=example,dc=com" <2>
    } }
  ] },
  "enabled": true
}
--------------------------------------------------

<1> The Active Directory distinguished name (DN) of the `users` group.
<2> The Active Directory distinguished name (DN) of the user `John Doe`.

Or, alternatively, configured via the role-mapping file:
[source, yaml]
------------------------------------------------------------
monitoring: <1>
  - "cn=admins,dc=example,dc=com" <2>
user:
  - "cn=users,dc=example,dc=com" <3>
  - "cn=admins,dc=example,dc=com"
  - "cn=John Doe,cn=contractors,dc=example,dc=com" <4>
------------------------------------------------------------
<1> The name of the role.
<2> The Active Directory distinguished name (DN) of the `admins` group.
<3> The Active Directory distinguished name (DN) of the `users` group.
<4> The Active Directory distinguished name (DN) of the user `John Doe`.

For more information, see 
<<mapping-roles>>.
--

. (Optional) Configure the `metadata` setting in the Active Directory realm to 
include extra properties in the user's metadata. 
+
--
By default, `ldap_dn` and `ldap_groups` are populated in the user's metadata. 
For more information, see 
<<ad-user-metadata>>. 
--
