GitLab Mattermost

You can run a GitLab Mattermost service on your GitLab server. Mattermost is not part of the single application that GitLab is. There is a good integration between Mattermost and GitLab, and our Linux package allows you to install it. However, Mattermost is a separate application from a separate company. GitLab Support cannot help you with Mattermost-specific questions beyond the integration with GitLab. If you need help with Mattermost itself, see the community support resources.

Prerequisites

Each release of GitLab Mattermost is compiled and manually tested 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 settings, you need two entries pointing to the same machine. For example, gitlab.example.com and mattermost.example.com.

GitLab Mattermost is disabled by default. To enable it:

Edit /etc/gitlab/gitlab.rb and add the Mattermost external URL:
```
mattermost_external_url 'https://mattermost.example.com'
```
Reconfigure GitLab:
```
sudo gitlab-ctl reconfigure
```
Confirm that GitLab Mattermost is reachable at https://mattermost.example.com and authorized to connect to GitLab. Authorizing Mattermost with GitLab allows users to use GitLab as an SSO provider.

The Linux package attempts to automatically authorize GitLab Mattermost with GitLab if the applications are running on the same server.

Automatic authorization requires access to the GitLab database. If the GitLab database is not available you need to manually authorize GitLab Mattermost for access to GitLab using the process described in the Authorize GitLab Mattermost section.

Configuring Mattermost

Starting in GitLab 11.0, Mattermost can be configured using the Mattermost System Console. An extensive list of Mattermost settings and where they can be set is available in the Mattermost documentation.

While using the System Console is recommended, you can also configure Mattermost using one of the following options:

Edit the Mattermost configuration directly through /var/opt/gitlab/mattermost/config.json.
Specify environment variables used to run Mattermost by changing the mattermost['env'] setting in gitlab.rb. Any settings configured in this way are disabled from the System Console and cannot be changed without restarting Mattermost.

Running GitLab Mattermost with HTTPS

Place the SSL certificate and SSL certificate key inside /etc/gitlab/ssl. If the directory doesn't exist, create it:

sudo mkdir -p /etc/gitlab/ssl
sudo chmod 755 /etc/gitlab/ssl
sudo cp mattermost.gitlab.example.key mattermost.gitlab.example.crt /etc/gitlab/ssl/

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

mattermost_external_url 'https://mattermost.gitlab.example'
mattermost_nginx['redirect_http_to_https'] = true

If you haven't named your certificate and key mattermost.gitlab.example.crt and mattermost.gitlab.example.key then you need to also add the full paths as shown below.

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

where mattermost-nginx.crt is the SSL certificate and mattermost-nginx.key is the SSL key.

Once the configuration is set, run sudo gitlab-ctl reconfigure to apply the changes.

Running GitLab Mattermost on its own server

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

mattermost_external_url 'http://mattermost.example.com'

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

Then follow the appropriate steps in the Authorize GitLab Mattermost section. Last, to enable integrations with GitLab add the following on the GitLab Server:

gitlab_rails['mattermost_host'] = "https://mattermost.example.com"

By default GitLab Mattermost requires all users to sign up with GitLab and disables the sign-up by email option. See Mattermost documentation on GitLab SSO.

Manually (re)authorizing GitLab Mattermost with GitLab

Reauthorize GitLab Mattermost

To reauthorize GitLab Mattermost, you first need to revoke the existing authorization. This can be done in the Settings > Applications area of GitLab. Then follow the steps below to complete authorization.

Authorize GitLab Mattermost

Navigate to the Settings > Applications area in GitLab. Create a new application and for the Redirect URI use the following (replace http with https if you use HTTPS):

http://mattermost.example.com/signup/gitlab/complete
http://mattermost.example.com/login/gitlab/complete

Make sure to select the Trusted and Confidential settings. Under Scopes, select read_user. Then, choose Save application.

Once the application is created you are provided with an Application ID and Secret. One other piece of information needed is the URL of GitLab instance. Return to the server running GitLab Mattermost and edit the /etc/gitlab/gitlab.rb configuration file as follows using the values you received above:

mattermost['gitlab_enable'] = true
mattermost['gitlab_id'] = "12345656"
mattermost['gitlab_secret'] = "123456789"
mattermost['gitlab_scope'] = "read_user"
mattermost['gitlab_auth_endpoint'] = "http://gitlab.example.com/oauth/authorize"
mattermost['gitlab_token_endpoint'] = "http://gitlab.example.com/oauth/token"
mattermost['gitlab_user_api_endpoint'] = "http://gitlab.example.com/api/v4/user"

Save the changes and then run sudo gitlab-ctl reconfigure. If there are no errors your GitLab and GitLab Mattermost should be configured correctly.

Specify numeric user and group identifiers

The Linux pacakage 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 to apply the changes.

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 to apply the changes.

Connecting to the bundled PostgreSQL database

If you need to connect to the bundled PostgreSQL database and are using the default Linux package database configuration, you can connect as the PostgreSQL superuser:

sudo gitlab-psql -d mattermost_production

Back up GitLab Mattermost

GitLab Mattermost is not included in the regular Linux package backup Rake task.

The general Mattermost backup and disaster recovery documentation can be used as a guide on what needs to be backed up.

Back up the bundled PostgreSQL database

If you need to back up the bundled PostgreSQL database and are using the default Linux package database configuration, you can back up using this command:

sudo -i -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

Back up the `data` directory and `config.json`

Mattermost has a data directory and config.json file that need to be backed up as well:

sudo tar -zcvf mattermost_data_$(date --rfc-3339=date).gz -C /var/opt/gitlab/mattermost data config.json

Restore GitLab Mattermost

If you have previously created a backup of GitLab Mattermost, you can run the following commands to restore it:

# Stop Mattermost so we don't have any open database connections
sudo gitlab-ctl stop mattermost

# Drop the Mattermost database
sudo -u gitlab-psql /opt/gitlab/embedded/bin/dropdb -U gitlab-psql -h /var/opt/gitlab/postgresql -p 5432 mattermost_production

# Create the Mattermost database
sudo -u gitlab-psql /opt/gitlab/embedded/bin/createdb -U gitlab-psql -h /var/opt/gitlab/postgresql -p 5432 mattermost_production

# Perform the database restore
# Replace /tmp/mattermost_dbdump_2021-08-05.sql.gz with your backup
sudo -u mattermost sh -c "zcat /tmp/mattermost_dbdump_2021-08-05.sql.gz | /opt/gitlab/embedded/bin/psql -U gitlab_mattermost -h /var/opt/gitlab/postgresql -p 5432 mattermost_production"

# Restore the data directory and config.json
# Replace /tmp/mattermost_data_2021-08-09.gz with your backup
sudo tar -xzvf /tmp/mattermost_data_2021-08-09.gz -C /var/opt/gitlab/mattermost

# Fix permissions if required
sudo chown -R mattermost:mattermost /var/opt/gitlab/mattermost/data
sudo chown mattermost:mattermost /var/opt/gitlab/mattermost/config.json

# Start Mattermost
sudo gitlab-ctl start mattermost

Mattermost Command Line Tools (CLI)

mmctl is a CLI tool for the Mattermost server which is installed locally and uses the Mattermost API, but may also be used remotely. You must configure Mattermost either for local connections or authenticate as an administrator with local login credentials (not through GitLab SSO). The executable is located at /opt/gitlab/embedded/bin/mmctl.

Use `mmctl` through a local connection

For local connections, the mmctl binary and Mattermost must be run from the same server. To enable the local socket:

Edit /var/opt/gitlab/mattermost/config.json, and add the following lines:

{
    "ServiceSettings": {
       ...
        "EnableLocalMode": true,
        "LocalModeSocketLocation": "/var/tmp/mattermost_local.socket",
        ...
    }
}

Restart Mattermost:
```
sudo gitlab-ctl restart mattermost
```

You can then use sudo /opt/gitlab/embedded/bin/mmctl --local to run mmctl commands on your Mattermost instance.

For example, to show the list of users:

$ sudo /opt/gitlab/embedded/bin/mmctl --local user list

13dzo5bmg7fu8rdox347hbfxde: appsbot (appsbot@localhost)
tbnkwjdug3dejcoddboo4yuomr: boards (boards@localhost)
wd3g5zpepjgbfjgpdjaas7yj6a: feedbackbot (feedbackbot@localhost)
8d3zzgpurp85zgf1q88pef73eo: playbooks (playbooks@localhost)
There are 4 users on local instance

Use `mmctl` through a remote connection

For remote connections or local connections where the socket cannot be used, create a non-SSO user and give that user administrator privileges. Those credentials can then be used to authenticate mmctl:

$ /opt/gitlab/embedded/bin/mmctl auth login http://mattermost.example.com

Connection name: test
Username: local-user
Password:
 credentials for "test": "local-user@http://mattermost.example.com" stored

Configuring GitLab and Mattermost integrations

You can use the plugin to subscribe Mattermost to receive notifications about issues, merge requests, and pull requests as well as personal notifications regarding merge request reviews, unread messages, and task assignments. If you want to use slash commands to perform actions such as creating and viewing issues, or to trigger deployments use GitLab Mattermost slash commands.

The plugin and slash commands can be used together or individually.

Email Notifications

Setting up SMTP for GitLab Mattermost

These settings are configured through the Mattermost System Console by the System Administrator. On the Environment > SMTP tab of the System Console, you can enter the SMTP credentials given by your SMTP provider, or 127.0.0.1 and port 25 to use sendmail. More information on the specific settings that are needed is available in the Mattermost documentation.

These settings can also be configured in /var/opt/gitlab/mattermost/config.json.

Email batching

Enabling this feature allows users to control how often they receive email notifications.

Email batching can be enabled in the Mattermost System Console by navigating to the Environment > SMTP tab, and setting the Enable Email Batching setting to True.

This setting can also be configured in /var/opt/gitlab/mattermost/config.json.

Upgrading GitLab Mattermost

Below is a list of Mattermost versions for GitLab 14.0 and later:

GitLab version	Mattermost version
16.2	7.10
16.1	7.10
16.0	7.10
15.11	7.9
15.10	7.8
15.9	7.7
15.8	7.5
15.7	7.5
15.6	7.4
15.5	7.3
15.4	7.2
15.3	7.1
15.2	7.0
15.1	6.7
15.0	6.6
14.10	6.5
14.9	6.4
14.8	6.3
14.7	6.2
14.6	6.1
14.5	5.39
14.4	5.39
14.3	5.38
14.2	5.37
14.1	5.36
14.0	5.35

GitLab 14.5 remained on Mattermost 5.39.
GitLab 14.6 updates to Mattermost 6.1 instead of 6.0.
GitLab 15.8 remained on Mattermost 7.5.
GitLab 16.1 and 16.2 remained on Mattermost 7.10.

NOTE: When upgrading the Mattermost version, it is essential to check the Important Upgrade Notes for Mattermost to address any changes or migrations that need to be performed.

GitLab Mattermost can be upgraded through the regular Linux package update process. When upgrading previous versions of GitLab, the update process can only be used if Mattermost configuration settings have not been changed outside of GitLab. That is, no changes to the Mattermost config.json file have been made - either directly or via the Mattermost System Console, which saves changes to config.json.

If you have only configured Mattermost using gitlab.rb, you can upgrade GitLab using the Linux package and then run gitlab-ctl reconfigure to upgrade GitLab Mattermost to the latest version.

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

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, the Linux package should be able to upgrade GitLab Mattermost from one version to the next.
Migrate Mattermost outside of the directory controlled by the Linux package so it can be administered and upgraded independently. Follow the Mattermost Migration Guide to move your Mattermost configuration settings and data to another directory or server independent from the Linux package.

For a complete list of upgrade notices and special considerations for older versions, see the Mattermost documentation.

Upgrading GitLab Mattermost to 14.6

GitLab 14.6 ships with Mattermost 6.1 including potentially long running database migrations for Mattermost 6.0. For information about upgrading and for ways to reduce the downtime caused by those migrations, read the Important Upgrade Notes for both versions. If you need to perform any manual migrations, connect to the bundled PostgreSQL database.

NOTE: The Mattermost upgrade notes refer to different impacts when used with a PostgreSQL versus a MySQL database. The GitLab Mattermost included with the Linux package uses a PostgreSQL database.

OAuth 2.0 sequence diagram

The following image is a sequence diagram for how GitLab works as an OAuth 2.0 provider for Mattermost. You can use this to troubleshoot errors in getting the integration to work:

sequenceDiagram
    User->>Mattermost: GET https://mm.domain.com
    Note over Mattermost, GitLab: Obtain access code
    Mattermost->>GitLab: GET https://gitlab.domain.com/oauth/authorize
    Note over User, GitLab: GitLab user signs in (if necessary)
    Note over GitLab: GitLab verifies client_id matches an OAuth application
    GitLab->>User: GitLab asks user to authorize Mattermost OAuth app
    User->>GitLab: User selects 'Allow'
    Note over GitLab: GitLab verifies redirect_uri matches list of valid URLs
    GitLab->>User: 302 redirect: https://mm.domain.com/signup/gitlab/complete
    User->>Mattermost: GET https://mm.domain.com/signup/gitlab/complete
    Note over Mattermost, GitLab: Exchange access code for access token
    Mattermost->>GitLab: POST http://gitlab.domain.com/oauth/token
    GitLab->>GitLab: Doorkeeper::TokensController#35;create
    GitLab->>Mattermost: Access token
    Note over Mattermost, GitLab: Mattermost looks up GitLab user
    Mattermost->>GitLab: GET https://gitlab.domain.com/api/v4/user
    GitLab->>Mattermost: User details
    Mattermost->>User: Mattermost/GitLab user ready

Community support resources

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

Troubleshooting Mattermost issues.
Mattermost GitLab Issues Support Handbook.
GitLab Mattermost issue tracker for verified bugs with repro steps.