GitLab Documentation

GitLab Mattermost

You can run a GitLab Mattermost service on your GitLab server.

Documentation version

Make sure you view this guide from the tag (version) of GitLab you would like to install. In most cases this should be the highest numbered production tag (without rc in it). You can select the tag in the version dropdown in the top left corner of GitLab (below the menu bar).

If the highest number stable branch is unclear please check the GitLab Blog for installation guide links by version.


GitLab Mattermost is compiled and manually tested each release on an AMD 64 chipset for Linux. ARM chipsets and operating systems, like Raspberry PI, are not supported.

Getting started

GitLab Mattermost expects to run on its own virtual host. In your DNS you would then have two entries pointing to the same machine, e.g. and

GitLab Mattermost is disabled by default, to enable it just tell omnibus-gitlab what the external URL for Mattermost server is:

# in /etc/gitlab/gitlab.rb
mattermost_external_url ''

After you run sudo gitlab-ctl reconfigure, your GitLab Mattermost should now be reachable at and authorized to connect to GitLab. Authorising Mattermost with GitLab will allow users to use GitLab as SSO provider.

Omnibus-gitlab package will attempt to automatically authorise GitLab Mattermost with GitLab if applications are running on the same server. This is because automatic authorisation requires access to GitLab database. If GitLab database is not available you will need to manually authorise GitLab Mattermost for access to GitLab.

Running GitLab Mattermost on its own server

If you want to run GitLab and GitLab Mattermost on two separate servers you can use the following settings on the GitLab Mattermost server to effectively disable the GitLab service bundled into the Omnibus package. The GitLab services will still be set up on your GitLab Mattermost server, but they will not accept user requests or consume system resources.

mattermost_external_url ''

# Tell GitLab Mattermost to integrate with

mattermost['gitlab_enable'] = true
mattermost['gitlab_id'] = "12345656"
mattermost['gitlab_secret'] = "123456789"
mattermost['gitlab_scope'] = ""
mattermost['gitlab_auth_endpoint'] = ""
mattermost['gitlab_token_endpoint'] = ""
mattermost['gitlab_user_api_endpoint'] = ""

# Shut down GitLab services on the Mattermost server
gitlab_rails['enable'] = false

where Secret and Id are application secret and application id received when creating new Application authorization in GitLab admin section.

To enable integrations with GitLab, add the following on the GitLab Server:

gitlab_rails['mattermost_host'] = ""

Optionally, you can set mattermost['email_enable_sign_up_with_email'] = false to force all users to sign-up with GitLab only. See Mattermost documentation on GitLab SSO.

Manually (re)authorising GitLab Mattermost with GitLab

Authorise GitLab Mattermost

To do this, using browser navigate to the admin area of GitLab, Application section. Create a new application and for the callback URL use: and (replace http with https if you use https).

Once the application is created you will receive an Application ID and Secret. One other information needed is the URL of GitLab instance.

Now, go to the GitLab server and edit the /etc/gitlab/gitlab.rb configuration file.

In gitlab.rb use the values you've received above:

mattermost['gitlab_enable'] = true
mattermost['gitlab_id'] = "12345656"
mattermost['gitlab_secret'] = "123456789"
mattermost['gitlab_scope'] = ""
mattermost['gitlab_auth_endpoint'] = ""
mattermost['gitlab_token_endpoint'] = ""
mattermost['gitlab_user_api_endpoint'] = ""

Save the changes and then run sudo gitlab-ctl reconfigure.

If there are no errors your GitLab and GitLab Mattermost should be configured correctly.

Reauthorise GitLab Mattermost

To reauthorise GitLab Mattermost you will first need to revoke access of the existing authorisation. This can be done in the Admin area of GitLab under Applications. Once that is done follow the steps in the Authorise GitLab Mattermost section.

Running GitLab Mattermost with HTTPS

Place the ssl certificate and ssl certificate key inside of /etc/gitlab/ssl directory. If directory doesn't exist, create one.

In /etc/gitlab/gitlab.rb specify the following configuration:

mattermost_external_url 'https://mattermost.gitlab.example'

mattermost_nginx['redirect_http_to_https'] = true
mattermost_nginx['ssl_certificate'] = "/etc/gitlab/ssl/mattermost-nginx.crt"
mattermost_nginx['ssl_certificate_key'] = "/etc/gitlab/ssl/mattermost-nginx.key"
mattermost['service_use_ssl'] = true

where mattermost-nginx.crt and mattermost-nginx.key are ssl cert and key, respectively. Once the configuration is set, run sudo gitlab-ctl reconfigure for the changes to take effect.

Email Notifications

Setting up SMTP for GitLab Mattermost

By default, mattermost['email_enable_sign_up_with_email'] = true which allows team creation and account signup using email and password. This should be false if you're using only an external authentication source such as GitLab.

SMTP configuration depends on SMTP provider used. Note that the configuration keys used are not the same as the ones that the main GitLab application uses, for example the SMTP user in Mattermost is email_smtp_username and not smtp_user_name.

If you are using SMTP without TLS minimal configuration in /etc/gitlab/gitlab.rb contains:

mattermost['email_enable_sign_in_with_email'] = false
mattermost['email_enable_sign_up_with_email'] = false
mattermost['email_send_email_notifications'] = true
mattermost['email_smtp_auth'] = true
mattermost['email_smtp_username'] = "username"
mattermost['email_smtp_password'] = "password"
mattermost['email_smtp_server'] = ""
mattermost['email_smtp_port'] = "465"
mattermost['email_connection_security'] = nil
mattermost['email_feedback_name'] = "GitLab Mattermost"
mattermost['email_feedback_email'] = ""
mattermost['email_skip_server_certificate_verification'] = false

If you are using TLS, configuration can look something like this:

mattermost['email_enable_sign_up_with_email'] = true
mattermost['email_enable_sign_up_with_email'] = false
mattermost['email_send_email_notifications'] = true
mattermost['email_smtp_auth'] = true
mattermost['email_smtp_username'] = "username"
mattermost['email_smtp_password'] = "password"
mattermost['email_smtp_server'] = ""
mattermost['email_smtp_port'] = "587"
mattermost['email_connection_security'] = 'TLS' # Or 'STARTTLS'
mattermost['email_feedback_name'] = "GitLab Mattermost"
mattermost['email_feedback_email'] = ""
mattermost['email_skip_server_certificate_verification'] = false

email_connection_security depends on your SMTP provider so you need to verify which of TLS or STARTTLS is valid for your provider.

Email Batching

Enabling this feature allows users to control how often they receive email notifications. Configuring the site URL, including protocol and port, is required:

mattermost['service_site_url'] = ''
mattermost['email_enable_batching'] = true

Once the configuration is set, run sudo gitlab-ctl reconfigure for the changes to take effect.

For additional configuration settings, see the Mattermost documentation.

Community Support Resources

For help and support around your GitLab Mattermost deployment please see:

Upgrading GitLab Mattermost

Note: These upgrade instructions are for GitLab Version 8.9 (Mattermost v3.1.0) and above. For upgrading versions prior to GitLab 8.9, additional steps are required.

Below is a list of Mattermost versions for GitLab 9.0 and later:

GitLab Version Mattermost Version
9.0, 9.1 3.7
9.2 3.9
9.3 3.10
9.4 4.0
9.5 4.1
10.0 4.2
10.1 4.3

It is possible to skip upgrade versions starting from Mattermost v3.1. For example, Mattermost v3.1.0 in GitLab 8.9 can upgrade directly to Mattermost v3.4.0 in GitLab 8.12.

GitLab Mattermost can be upgraded through the regular GitLab omnibus update process provided Mattermost configuration settings have not been changed outside of GitLab. This means no changes to Mattermost's config.json file have been made, either directly or via the Mattermost System Console which saves back changes to config.json.

If this is the case, upgrading GitLab using omnibus and running gitlab-ctl reconfigure should upgrade GitLab Mattermost to the next version.

If this is not the case, there are two options:

  1. Update gitlab.rb with the changes done to config.json This might require adding some parameters as not all settings in config.json are available in gitlab.rb. Once complete, GitLab omnibus should be able to upgrade GitLab Mattermost from one version to the next.
  2. Migrate Mattermost outside of the directory controlled by GitLab omnibus so it can be administered and upgraded independently (see below).

Special Considerations

Consider these notes when upgrading GitLab Mattermost:

  1. Starting in Mattermost v4.2, user-supplied URLs such as those used for Open Graph metadata, webhooks, or slash commands will no longer be allowed to connect to reserved IP addresses including loopback or link-local addresses used for internal networks by default. This change may cause private integrations to break in testing environments, which may point to a URL such as
    • If you point private integrations to such URLs, you may whitelist such domains, IP addresses, or CIDR notations via the AllowedUntrustedInternalConnections config setting in your local environment. Although not recommended, you may also whitelist the addresses in your production environments.
    • Push notification, OAuth 2.0 and WebRTC server URLs are trusted and not affected by this setting.
  2. Starting in Mattermost v4.2, Mattermost now handles multiple content-types for integrations. Make sure your integrations have been set to use the appropriate content-type.
  3. Security related changes were made in Mattermost v3.9 that cause any previously created team invite links, password reset links, and email verification links to no longer work. You must update any place where you have published these links.

For a complete list of upgrade notices from older versions, see the Mattermost documentation.

Upgrading GitLab Mattermost from versions prior to 8.9

After upgrading to GitLab 8.9 additional steps are require before restarting the Mattermost server to enable multi-account support in Mattermost 3.1.

  1. Confirm you are starting with version GitLab 8.8.
  2. Backup your Mattermost database.
    • This is especially important in the 8.9 upgrade since the database upgrade cannot be reversed and is incompatible with previous versions.
    • If you use a default omnibus install you can use this command: sudo -u gitlab-psql -- /opt/gitlab/embedded/bin/pg_dump -h /var/opt/gitlab/postgresql mattermost_production | gzip > mattermost_dbdump_$(date --rfc-3339=date).sql.gz
  3. Configure two settings.
    • In /etc/gitlab/gitlab.rb set mattermost['db2_backup_created'] = true to verify your database backup is complete.
    • In /etc/gitlab/gitlab.rb set mattermost['db2_team_name'] = "TEAMNAME" where TEAMNAME is the name of your primary team in Mattermost.
      • If you use only one team in Mattermost, this should be the name of the team.
      • If you use multiple teams, this should be the name of the team most commonly used.
        • When Mattermost 3.1 upgrades the database with multi-team account support user accounts on the primary team are preserved, and accounts with duplciate emails or usernames in other teams are renamed.
        • Users with renamed accounts receive instructions by email on how to switch from using multiple accounts into one multi-team account.
        • For more information, please review the Mattermost 3.0 upgrade documentation.
  4. Run your GitLab 8.9 upgrade as normal.
    • This installs the Mattermost 3.1 binary and will attempt to auto-upgrade the database.
    • Your Mattermost database will be upgraded to version 3.1 and the server should start.
    • You'll see an "Automatic database upgrade failed" error on the command line and Mattermost will not start if something goes wrong.

If you experience issues you can run an interactive upgrade using:

sudo -u mattermost -i bash
cd /opt/gitlab/embedded/service/mattermost
/opt/gitlab/embedded/bin/mattermost -config='/var/opt/gitlab/mattermost/config.json' -upgrade_db_30

Log in as root or user with super user access and re-run sudo gitlab-ctl reconfigure.

For any questions, please visit the GitLab Mattermost troubleshooting forum and share any relevant portions of mattermost.log along with the step at which you encountered issues.

Migrating Mattermost outside of GitLab

Follow the Mattermost Migration Guide to move your Mattermost configuration settings and data to another directory or server independent from GitLab omnibus.

Upgrading GitLab Mattermost outside of GitLab

If you choose to upgrade Mattermost outside of GitLab's omnibus automation, please follow this guide.

Administering GitLab Mattermost

GitLab notifications in Mattermost

There are multiple ways to send notifications depending on how much control you'd like over the messages.

If you are using the Omnibus edition, enable incoming webhooks from the gitlab.rb file not the System Console or your settings will be lost the next time you upgrade GitLab Omnibus.

mattermost['service_enable_incoming_webhooks'] = true

Setting up Mattermost as a Slack project service integration:

Mattermost is "Slack-compatible, not Slack-limited" so if you like Slack's default formatting you can use their project service option to set up Mattermost integration:

  1. In Mattermost, go to System ConsoleService Settings and turn on Enable Incoming Webhooks
  2. Go to Account SettingsIntegrationsIncoming Webhooks
  3. Select a channel and click *Add and copy the Webhook URL
  4. In GitLab, paste the Webhook URL into Webhook under your project’s SettingsServicesSlack
  5. Enter Username for how you would like to name the account that posts the notifications
  6. Select Triggers for GitLab events on which you'd like to receive notifications
  7. Click Save changes then Test settings to make sure everything is working

Any issues, please see the Mattermost Troubleshooting Forum.

Setting up GitLab integration service for Mattermost

You can also set up the open source integration service to let you configure notifications on GitLab issues, pushes, build events, merge requests and comments to be delivered to selected Mattermost channels.

This integration lets you completely control how notifications are formatted and, unlike Slack, offers full markdown support.

The source code can be modified to support not only GitLab, but any in-house applications you may have that support webhooks. Also see:


Specify numeric user and group identifiers

omnibus-gitlab creates a user and group mattermost. You can specify the numeric identifiers for these users in /etc/gitlab/gitlab.rb as follows.

mattermost['uid'] = 1234
mattermost['gid'] = 1234

Run sudo gitlab-ctl reconfigure for the changes to take effect.

Setting custom environment variables

If necessary you can set custom environment variables to be used by Mattermost via /etc/gitlab/gitlab.rb. This can be useful if the Mattermost server is operated behind a corporate internet proxy. In /etc/gitlab/gitlab.rb supply a mattermost['env'] with a hash value. For example:

mattermost['env'] = {"http_proxy" => "my_proxy", "https_proxy" => "my_proxy", "no_proxy" => "my_no_proxy"}

Run sudo gitlab-ctl reconfigure for the changes to take effect.

OAuth2 Sequence Diagram

The following image is a sequence diagram for how GitLab works as an OAuth2 provider for Mattermost. It may be useful to use this to troubleshoot errors in getting the integration to work:

sequence diagram