Allow LDAP failover

Fixes: https://gitlab.com/gitlab-org/gitlab/-/issues/139
Changelog: added

doc/administration/auth/ldap/index.md

@@ -158,8 +158,9 @@ These configuration settings are available:
 | Setting            | Description | Required | Examples |
 |--------------------|-------------|----------|----------|
 | `label`            | A human-friendly name for your LDAP server. It is displayed on your sign-in page. | **{check-circle}** Yes | `'Paris'` or `'Acme, Ltd.'` |
-| `host`             | IP address or domain name of your LDAP server. | **{check-circle}** Yes | `'ldap.mydomain.com'` |
-| `port`             | The port to connect with on your LDAP server. Always an integer, not a string. | **{check-circle}** Yes | `389` or `636` (for SSL) |
+| `host`             | IP address or domain name of your LDAP server. Ignored when `hosts` is defined. | **{check-circle}** Yes | `'ldap.mydomain.com'` |
+| `port`             | The port to connect with on your LDAP server. Always an integer, not a string. Ignored when `hosts` is defined. | **{check-circle}** Yes | `389` or `636` (for SSL) |
+| `hosts`            | An array of host and port pairs to open connections. This setting takes precedence over `host` and `port`. | **{dotted-circle}** No | `[['ldap1.mydomain.com', 636], ['ldap2.mydomain.com', 636]]` |
 | `uid`              | LDAP attribute for username. Should be the attribute, not the value that maps to the `uid`. | **{check-circle}** Yes | `'sAMAccountName'` or `'uid'` or `'userPrincipalName'` |
 | `bind_dn`          | The full DN of the user you bind with. | **{dotted-circle}** No | `'america\momo'` or `'CN=Gitlab,OU=Users,DC=domain,DC=com'` |
 | `password`         | The password of the bind user. | **{dotted-circle}** No | `'your_great_password'` |

lib/gitlab/auth/ldap/config.rb

@@ -206,7 +206,8 @@ module Gitlab
         def base_options
           {
             host: options['host'],
-            port: options['port']
+            port: options['port'],
+            hosts: options['hosts']
           }
         end
 

spec/lib/gitlab/auth/ldap/config_spec.rb

@@ -121,10 +121,40 @@ AtlErSqafbECNDSwS5BX8yDpu5yRBJ4xegO/rNlmb8ICRYkuJapD1xXicFOsmfUK
       expect(config.adapter_options).to eq(
         host: 'ldap.example.com',
         port: 386,
+        hosts: nil,
         encryption: nil
       )
     end
 
+    it 'includes failover hosts when set' do
+      stub_ldap_config(
+        options: {
+          'host'                => 'ldap.example.com',
+          'port'                => 686,
+          'hosts'               => [
+            ['ldap1.example.com', 636],
+            ['ldap2.example.com', 636]
+          ],
+          'encryption'          => 'simple_tls',
+          'verify_certificates' => true,
+          'bind_dn'             => 'uid=admin,dc=example,dc=com',
+          'password'            => 'super_secret'
+        }
+      )
+
+      expect(config.adapter_options).to include({
+        hosts: [
+          ['ldap1.example.com', 636],
+          ['ldap2.example.com', 636]
+        ],
+        auth: {
+          method: :simple,
+          username: 'uid=admin,dc=example,dc=com',
+          password: 'super_secret'
+        }
+      })
+    end
+
     it 'includes authentication options when auth is configured' do
       stub_ldap_config(
         options: {