LDAP synchronization

If you have configured LDAP to work with GitLab, GitLab can automatically synchronize users and groups. This process updates user and group information.

You can change when synchronization occurs.

User sync

Once per day, GitLab runs a worker to check and update GitLab users against LDAP.

The process executes the following access checks:

  • Ensure the user is still present in LDAP.
  • If the LDAP server is Active Directory, ensure the user is active (not blocked/disabled state). This check is performed only if active_directory: true is set in the LDAP configuration.

In Active Directory, a user is marked as disabled/blocked if the user account control attribute (userAccountControl:1.2.840.113556.1.4.803) has bit 2 set.

For more information, see Bitmask Searches in LDAP.

The user is set to an ldap_blocked state in GitLab if the previous conditions fail. This means the user cannot sign in or push or pull code.

The process also updates the following user information:

  • Email address
  • SSH public keys (if sync_ssh_keys is set)
  • Kerberos identity (if Kerberos is enabled)

The LDAP sync process:

  • Updates existing users.
  • Creates new users on first sign in.

Adjust LDAP user sync schedule

By default, GitLab runs a worker once per day at 01:30 a.m. server time to check and update GitLab users against LDAP.

You can manually configure LDAP user sync times by setting the following configuration values, in cron format. If needed, you can use a crontab generator. The example below shows how to set LDAP user sync to run once every 12 hours at the top of the hour.

Omnibus installations

  1. Edit /etc/gitlab/gitlab.rb:

    gitlab_rails['ldap_sync_worker_cron'] = "0 */12 * * *"
    
  2. Reconfigure GitLab for the changes to take effect.

Source installations

  1. Edit config/gitlab.yaml:

    cron_jobs:
      ldap_sync_worker_cron:
        "0 */12 * * *"
    
  2. Restart GitLab for the changes to take effect.

Group sync

If your LDAP supports the memberof property, when the user signs in for the first time GitLab triggers a sync for groups the user should be a member of. That way they don’t have to wait for the hourly sync to be granted access to their groups and projects.

A group sync process runs every hour on the hour, and group_base must be set in LDAP configuration for LDAP synchronizations based on group CN to work. This allows GitLab group membership to be automatically updated based on LDAP group members.

The group_base configuration should be a base LDAP ‘container’, such as an ‘organization’ or ‘organizational unit’, that contains LDAP groups that should be available to GitLab. For example, group_base could be ou=groups,dc=example,dc=com. In the configuration file it looks like the following.

Omnibus configuration

  1. Edit /etc/gitlab/gitlab.rb:

    gitlab_rails['ldap_servers'] = {
    'main' => {
      # snip...
      'group_base' => 'ou=groups,dc=example,dc=com',
      }
    }
    
  2. Apply your changes to GitLab.

Source configuration

  1. Edit /home/git/gitlab/config/gitlab.yml:

    production:
      ldap:
        servers:
          main:
            # snip...
            group_base: ou=groups,dc=example,dc=com
    
  2. Restart GitLab for the changes to take effect.

To take advantage of group sync, group Owners or users with the Maintainer role must create one or more LDAP group links.

For information on adding group links by using CNs and filters, refer to the GitLab groups documentation.

Administrator sync

As an extension of group sync, you can automatically manage your global GitLab administrators. Specify a group CN for admin_group and all members of the LDAP group are given administrator privileges. The configuration looks like the following.

note
Administrators are not synced unless group_base is also specified alongside admin_group. Also, only specify the CN of the admin_group, as opposed to the full DN. Additionally, if an LDAP user has an admin role, but is not a member of the admin_group group, GitLab revokes their admin role when syncing.

Omnibus configuration

  1. Edit /etc/gitlab/gitlab.rb:

    gitlab_rails['ldap_servers'] = {
    'main' => {
      # snip...
      'group_base' => 'ou=groups,dc=example,dc=com',
      'admin_group' => 'my_admin_group',
      }
    }
    
  2. Apply your changes to GitLab.

Source configuration

  1. Edit /home/git/gitlab/config/gitlab.yml:

    production:
      ldap:
        servers:
          main:
            # snip...
            group_base: ou=groups,dc=example,dc=com
            admin_group: my_admin_group
    
  2. Restart GitLab for the changes to take effect.

Global group memberships lock

Introduced in GitLab 12.0.

“Lock memberships to LDAP synchronization” setting allows instance administrators to lock down user abilities to invite new members to a group.

When enabled, the following applies:

  • Only administrator can manage memberships of any group including access levels.
  • Users are not allowed to share project with other groups or invite members to a project created in a group.

To enable it, you must:

  1. Configure LDAP.
  2. On the top bar, select Menu > Admin.
  3. On the left sidebar, select Settings > General.
  4. Expand the Visibility and access controls section.
  5. Ensure the Lock memberships to LDAP synchronization checkbox is selected.

Adjust LDAP group sync schedule

By default, GitLab runs a group sync process every hour, on the hour. The values shown are in cron format. If needed, you can use a Crontab Generator.

caution
Do not start the sync process too frequently as this could lead to multiple syncs running concurrently. This concern is primarily for installations with a large number of LDAP users. Review the LDAP group sync benchmark metrics to see how your installation compares before proceeding.

You can manually configure LDAP group sync times by setting the following configuration values. The example below shows how to set group sync to run once every two hours at the top of the hour.

Omnibus installations

  1. Edit /etc/gitlab/gitlab.rb:

    gitlab_rails['ldap_group_sync_worker_cron'] = "0 */2 * * * *"
    
  2. Reconfigure GitLab for the changes to take effect.

Source installations

  1. Edit config/gitlab.yaml:

    cron_jobs:
      ldap_group_sync_worker_cron:
          "*/30 * * * *"
    
  2. Restart GitLab for the changes to take effect.

External groups

Using the external_groups setting allows you to mark all users belonging to these groups as external users. Group membership is checked periodically through the LdapGroupSync background task.

Omnibus configuration

  1. Edit /etc/gitlab/gitlab.rb:

    gitlab_rails['ldap_servers'] = {
    'main' => {
      # snip...
      'external_groups' => ['interns', 'contractors'],
      }
    }
    
  2. Apply your changes to GitLab.

Source configuration

  1. Edit config/gitlab.yaml:

    production:
      ldap:
        servers:
          main:
            # snip...
            external_groups: ['interns', 'contractors']
    
  2. Restart GitLab for the changes to take effect.

Group sync technical details

This section outlines what LDAP queries are executed and what behavior you can expect from group sync.

Group member access are downgraded from a higher level if their LDAP group membership changes. For example, if a user the Owner role in a group and the next group sync reveals they should only have the Developer role, their access is adjusted accordingly. The only exception is if the user is the last owner in a group. Groups need at least one owner to fulfill administrative duties.

Supported LDAP group types/attributes

GitLab supports LDAP groups that use member attributes:

  • member
  • submember
  • uniquemember
  • memberof
  • memberuid

This means group sync supports (at least) LDAP groups with the following object classes:

  • groupOfNames
  • posixGroup
  • groupOfUniqueNames

Other object classes should work if members are defined as one of the mentioned attributes.

Active Directory supports nested groups. Group sync recursively resolves membership if active_directory: true is set in the configuration file.

Nested group memberships

Nested group memberships are resolved only if the nested group is found in the configured group_base. For example, if GitLab sees a nested group with DN cn=nested_group,ou=special_groups,dc=example,dc=com but the configured group_base is ou=groups,dc=example,dc=com, cn=nested_group is ignored.

Queries

  • Each LDAP group is queried a maximum of one time with base group_base and filter (cn=<cn_from_group_link>).
  • If the LDAP group has the memberuid attribute, GitLab executes another LDAP query per member to obtain each user’s full DN. These queries are executed with base base, scope ‘base object’, and a filter depending on whether user_filter is set. Filter may be (uid=<uid_from_group>) or a joining of user_filter.

Benchmarks

Group sync was written to be as performant as possible. Data is cached, database queries are optimized, and LDAP queries are minimized. The last benchmark run revealed the following metrics:

For 20,000 LDAP users, 11,000 LDAP groups, and 1,000 GitLab groups with 10 LDAP group links each:

  • Initial sync (no existing members assigned in GitLab) took 1.8 hours
  • Subsequent syncs (checking membership, no writes) took 15 minutes

These metrics are meant to provide a baseline and performance may vary based on any number of factors. This benchmark was extreme and most instances don’t have near this many users or groups. Disk speed, database performance, network and LDAP server response time affects these metrics.