Gitaly Cluster

Gitaly, the service that provides storage for Git repositories, can be run in a clustered configuration to increase fault tolerance. In this configuration, every Git repository is stored on every Gitaly node in the cluster. Multiple clusters (or shards), can be configured.

NOTE: Note: Gitaly Clusters can be created using GitLab Core and higher tiers. However, technical support is limited to GitLab Premium and Ultimate customers only. Not available in GitLab.com.

Praefect is a router and transaction manager for Gitaly, and a required component for running a Gitaly Cluster.

Using a Gitaly Cluster increase fault tolerance by:

Replicating write operations to warm standby Gitaly nodes.
Detecting Gitaly node failures.
Automatically routing Git requests to an available Gitaly node.

The availability objectives for Gitaly clusters are:

Recovery Point Objective (RPO): Less than 1 minute.

Writes are replicated asynchronously. Any writes that have not been replicated to the newly promoted primary are lost.

Strong Consistency is planned to improve this to "no loss".
Recovery Time Objective (RTO): Less than 10 seconds.

Outages are detected by a health checks run by each Praefect node every second. Failover requires ten consecutive failed health checks on each Praefect node.

Faster outage detection is planned to improve this to less than 1 second.

The current version supports:

Eventual consistency of the secondary replicas.
Automatic failover from the primary to the secondary.
Reporting of possible data loss if replication queue is non empty.
Marking the newly promoted primary read only if possible data loss is detected.

Follow the HA Gitaly epic for improvements including horizontally distributing reads.

Requirements for configuring a Gitaly Cluster

The minimum recommended configuration for a Gitaly Cluster requires:

1 load balancer
1 PostgreSQL server (PostgreSQL 11 or newer)
3 Praefect nodes
3 Gitaly nodes (1 primary, 2 secondary)

See the design document for implementation details.

Setup Instructions

If you installed GitLab using the Omnibus package (highly recommended), follow the steps below:

Preparation
Configuring the Praefect database
Configuring the Praefect proxy/router
Configuring each Gitaly node (once for each Gitaly node)
Configure the load balancer
Updating the GitLab server configuration
Configure Grafana

Preparation

Before beginning, you should already have a working GitLab instance. Learn how to install GitLab.

Provision a PostgreSQL server (PostgreSQL 11 or newer). Configuration through the Omnibus GitLab distribution is not yet supported. Follow this issue for updates.

Prepare all your new nodes by installing GitLab.

1 Praefect node (minimal storage required)
3 Gitaly nodes (high CPU, high memory, fast storage)
1 GitLab server

You will need the IP/host address for each node.

LOAD_BALANCER_SERVER_ADDRESS: the IP/hots address of the load balancer
POSTGRESQL_SERVER_ADDRESS: the IP/host address of the PostgreSQL server
PRAEFECT_HOST: the IP/host address of the Praefect server
GITALY_HOST: the IP/host address of each Gitaly server
GITLAB_HOST: the IP/host address of the GitLab server

If you are using a cloud provider, you can look up the addresses for each server through your cloud provider's management console.

If you are using Google Cloud Platform, SoftLayer, or any other vendor that provides a virtual private cloud (VPC) you can use the private addresses for each cloud instance (corresponds to “internal address” for Google Cloud Platform) for PRAEFECT_HOST, GITALY_HOST, and GITLAB_HOST.

Secrets

The communication between components is secured with different secrets, which are described below. Before you begin, generate a unique secret for each, and make note of it. This will make it easy to replace these placeholder tokens with secure tokens as you complete the setup process.

GITLAB_SHELL_SECRET_TOKEN: this is used by Git hooks to make callback HTTP API requests to GitLab when accepting a Git push. This secret is shared with GitLab Shell for legacy reasons.
PRAEFECT_EXTERNAL_TOKEN: repositories hosted on your Praefect cluster can only be accessed by Gitaly clients that carry this token.
PRAEFECT_INTERNAL_TOKEN: this token is used for replication traffic inside your Praefect cluster. This is distinct from PRAEFECT_EXTERNAL_TOKEN because Gitaly clients must not be able to access internal nodes of the Praefect cluster directly; that could lead to data loss.
PRAEFECT_SQL_PASSWORD: this password is used by Praefect to connect to PostgreSQL.
GRAFANA_PASSWORD: this password is used to access the admin account in the Grafana dashboards.

We will note in the instructions below where these secrets are required.

PostgreSQL

NOTE: Note: do not store the GitLab application database and the Praefect database on the same PostgreSQL server if using Geo. The replication state is internal to each instance of GitLab and should not be replicated.

To complete this section you will need:

1 Praefect node
1 PostgreSQL server (PostgreSQL 11 or newer)
- An SQL user with permissions to create databases

During this section, we will configure the PostgreSQL server, from the Praefect node, using psql which is installed by Omnibus GitLab.

SSH into the Praefect node and login as root:
```
sudo -i
```
Connect to the PostgreSQL server with administrative access. This is likely the postgres user. The database template1 is used because it is created by default on all PostgreSQL servers.
```
/opt/gitlab/embedded/bin/psql -U postgres -d template1 -h POSTGRESQL_SERVER_ADDRESS
```
Create a new user praefect which will be used by Praefect. Replace PRAEFECT_SQL_PASSWORD with the strong password you generated in the preparation step.
```
CREATE ROLE praefect WITH LOGIN CREATEDB PASSWORD 'PRAEFECT_SQL_PASSWORD';
```
Reconnect to the PostgreSQL server, this time as the praefect user:
```
/opt/gitlab/embedded/bin/psql -U praefect -d template1 -h POSTGRESQL_SERVER_ADDRESS
```
Create a new database praefect_production. By creating the database while connected as the praefect user, we are confident they have access.
```
CREATE DATABASE praefect_production WITH ENCODING=UTF8;
```

The database used by Praefect is now configured.

Praefect

To complete this section you will need:

Configured PostgreSQL server, including:
- IP/host address (POSTGRESQL_SERVER_ADDRESS)
- password (PRAEFECT_SQL_PASSWORD)

Praefect should be run on a dedicated node. Do not run Praefect on the application server, or a Gitaly node.

SSH into the Praefect node and login as root:
```
sudo -i
```

Disable all other services by editing /etc/gitlab/gitlab.rb:

# Disable all other services on the Praefect node
postgresql['enable'] = false
redis['enable'] = false
nginx['enable'] = false
prometheus['enable'] = false
grafana['enable'] = false
puma['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false
gitaly['enable'] = false

# Enable only the Praefect service
praefect['enable'] = true

# Prevent database connections during 'gitlab-ctl reconfigure'
gitlab_rails['rake_cache_clear'] = false
gitlab_rails['auto_migrate'] = false

Configure Praefect to listen on network interfaces by editing /etc/gitlab/gitlab.rb:

praefect['listen_addr'] = '0.0.0.0:2305'

# Enable Prometheus metrics access to Praefect. You must use firewalls
# to restrict access to this address/port.
praefect['prometheus_listen_addr'] = '0.0.0.0:9652'

Configure a strong auth_token for Praefect by editing /etc/gitlab/gitlab.rb. This will be needed by clients outside the cluster (like GitLab Shell) to communicate with the Praefect cluster :
```
praefect['auth_token'] = 'PRAEFECT_EXTERNAL_TOKEN'
```

Configure Praefect to connect to the PostgreSQL database by editing /etc/gitlab/gitlab.rb.

You will need to replace POSTGRESQL_SERVER_ADDRESS with the IP/host address of the database, and PRAEFECT_SQL_PASSWORD with the strong password set above.

praefect['database_host'] = 'POSTGRESQL_SERVER_ADDRESS'
praefect['database_port'] = 5432
praefect['database_user'] = 'praefect'
praefect['database_password'] = 'PRAEFECT_SQL_PASSWORD'
praefect['database_dbname'] = 'praefect_production'

If you want to use a TLS client certificate, the options below can be used:

# Connect to PostreSQL using a TLS client certificate
# praefect['database_sslcert'] = '/path/to/client-cert'
# praefect['database_sslkey'] = '/path/to/client-key'

# Trust a custom certificate authority
# praefect['database_sslrootcert'] = '/path/to/rootcert'

By default Praefect will refuse to make an unencrypted connection to PostgreSQL. You can override this by uncommenting the following line:

# praefect['database_sslmode'] = 'disable'

Configure the Praefect cluster to connect to each Gitaly node in the cluster by editing /etc/gitlab/gitlab.rb.

In the example below we have configured one virtual storage (or shard) named storage-1. This cluster has three Gitaly nodes gitaly-1, gitaly-2, and gitaly-3, which will be replicas of each other.

Replace PRAEFECT_INTERNAL_TOKEN with a strong secret, which will be used by Praefect when communicating with Gitaly nodes in the cluster. This token is distinct from the PRAEFECT_EXTERNAL_TOKEN.

Replace GITALY_HOST with the IP/host address of the each Gitaly node.

More Gitaly nodes can be added to the cluster to increase the number of replicas. More clusters can also be added for very large GitLab instances.

NOTE: Note: The gitaly-1 node is currently denoted the primary. This can be used to manually fail from one node to another. This will be removed in the future.
```
# Name of storage hash must match storage name in git_data_dirs on GitLab
# server ('praefect') and in git_data_dirs on Gitaly nodes ('gitaly-1')
praefect['virtual_storages'] = {
  'storage-1' => {
    'gitaly-1' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN',
      'primary' => true
    },
    'gitaly-2' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN'
    },
    'gitaly-3' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN'
    }
  }
}
```
Save the changes to /etc/gitlab/gitlab.rb and reconfigure Praefect:
```
gitlab-ctl reconfigure
```
To ensure that Praefect has updated its Prometheus listen address, restart Gitaly:
```
gitlab-ctl restart praefect
```
Verify that Praefect can reach PostgreSQL:
```
sudo -u git /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml sql-ping
```
If the check fails, make sure you have followed the steps correctly. If you edit /etc/gitlab/gitlab.rb, remember to run sudo gitlab-ctl reconfigure again before trying the sql-ping command.

The steps above must be completed for each Praefect node!

Gitaly

NOTE: Note: Complete these steps for each Gitaly node.

To complete this section you will need:

Configured Praefect node
3 (or more) servers, with GitLab installed, to be configured as Gitaly nodes. These should be dedicated nodes, do not run other services on these nodes.

Every Gitaly server assigned to the Praefect cluster needs to be configured. The configuration is the same as a normal standalone Gitaly server, except:

the storage names are exposed to Praefect, not GitLab
the secret token is shared with Praefect, not GitLab

The configuration of all Gitaly nodes in the Praefect cluster can be identical, because we rely on Praefect to route operations correctly.

Particular attention should be shown to:

the gitaly['auth_token'] configured in this section must match the token value under praefect['virtual_storages'] on the Praefect node. This was set in the previous section. This document uses the placeholder PRAEFECT_INTERNAL_TOKEN throughout.
the storage names in git_data_dirs configured in this section must match the storage names under praefect['virtual_storages'] on the Praefect node. This was set in the previous section. This document uses gitaly-1, gitaly-2, and gitaly-3 as Gitaly storage names.

For more information on Gitaly server configuration, see our Gitaly documentation.

SSH into the Gitaly node and login as root:
```
sudo -i
```

Disable all other services by editing /etc/gitlab/gitlab.rb:

# Disable all other services on the Praefect node
postgresql['enable'] = false
redis['enable'] = false
nginx['enable'] = false
grafana['enable'] = false
puma['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false
prometheus_monitoring['enable'] = false

# Enable only the Gitaly service
gitaly['enable'] = true

# Enable Prometheus if needed
prometheus['enable'] = true

# Prevent database connections during 'gitlab-ctl reconfigure'
gitlab_rails['rake_cache_clear'] = false
gitlab_rails['auto_migrate'] = false

Configure Gitaly to listen on network interfaces by editing /etc/gitlab/gitlab.rb:

# Make Gitaly accept connections on all network interfaces.
# Use firewalls to restrict access to this address/port.
gitaly['listen_addr'] = '0.0.0.0:8075'

# Enable Prometheus metrics access to Gitaly. You must use firewalls
# to restrict access to this address/port.
gitaly['prometheus_listen_addr'] = '0.0.0.0:9236'

Configure a strong auth_token for Gitaly by editing /etc/gitlab/gitlab.rb. This will be needed by clients to communicate with this Gitaly nodes. Typically, this token will be the same for all Gitaly nodes.
```
gitaly['auth_token'] = 'PRAEFECT_INTERNAL_TOKEN'
```

Configure the GitLab Shell secret_token, and internal_api_url which are needed for git push operations.

If you have already configured Gitaly on its own server

gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'

# Configure the gitlab-shell API callback URL. Without this, `git push` will
# fail. This can be your front door GitLab URL or an internal load balancer.
# Examples: 'https://example.gitlab.com', 'http://1.2.3.4'
gitlab_rails['internal_api_url'] = 'http://GITLAB_HOST'

Configure the storage location for Git data by setting git_data_dirs in /etc/gitlab/gitlab.rb. Each Gitaly node should have a unique storage name (such as gitaly-1).

Instead of configuring git_data_dirs uniquely for each Gitaly node, it is often easier to have include the configuration for all Gitaly nodes on every Gitaly node. This is supported because the Praefect virtual_storages configuration maps each storage name (such as gitaly-1) to a specific node, and requests are routed accordingly. This means every Gitaly node in your fleet can share the same configuration.
```
# You can include the data dirs for all nodes in the same config, because
# Praefect will only route requests according to the addresses provided in the
# prior step.
git_data_dirs({
  "gitaly-1" => {
    "path" => "/var/opt/gitlab/git-data"
  },
  "gitaly-2" => {
    "path" => "/var/opt/gitlab/git-data"
  },
  "gitaly-3" => {
    "path" => "/var/opt/gitlab/git-data"
  }
})
```
Save the changes to /etc/gitlab/gitlab.rb and reconfigure Gitaly:
```
gitlab-ctl reconfigure
```
To ensure that Gitaly has updated its Prometheus listen address, restart Gitaly:
```
gitlab-ctl restart gitaly
```

The steps above must be completed for each Gitaly node!

After all Gitaly nodes are configured, you can run the Praefect connection checker to verify Praefect can connect to all Gitaly servers in the Praefect config.

SSH into the Praefect node and run the Praefect connection checker:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dial-nodes

Load Balancer

In a highly available Gitaly configuration, a load balancer is needed to route internal traffic from the GitLab application to the Praefect nodes. The specifics on which load balancer to use or the exact configuration is beyond the scope of the GitLab documentation.

We hope that if you’re managing HA systems like GitLab, you have a load balancer of choice already. Some examples include HAProxy (open-source), Google Internal Load Balancer, AWS Elastic Load Balancer, F5 Big-IP LTM, and Citrix Net Scaler. This documentation will outline what ports and protocols you need configure.

LB Port	Backend Port	Protocol
2305	2305	TCP

GitLab

To complete this section you will need:

Configured Praefect node
Configured Gitaly nodes

The Praefect cluster needs to be exposed as a storage location to the GitLab application. This is done by updating the git_data_dirs.

Particular attention should be shown to:

the storage name added to git_data_dirs in this section must match the storage name under praefect['virtual_storages'] on the Praefect node. This was set in the Praefect section of this guide. This document uses storage-1 as the Praefect storage name.

SSH into the GitLab node and login as root:
```
sudo -i
```
Configure the external_url so that files could be served by GitLab by proper endpoint access by editing /etc/gitlab/gitlab.rb:

You will need to replace GITLAB_SERVER_URL with the real external facing URL on which current GitLab instance is serving:
```
external_url 'GITLAB_SERVER_URL'
```
Add the Praefect cluster as a storage location by editing /etc/gitlab/gitlab.rb.

You will need to replace:
- LOAD_BALANCER_SERVER_ADDRESS with the IP address or hostname of the load balancer.
- GITLAB_HOST with the IP address or hostname of the GitLab server
- PRAEFECT_EXTERNAL_TOKEN with the real secret
```
git_data_dirs({
  "default" => {
    "gitaly_address" => "tcp://GITLAB_HOST:8075"
  },
  "storage-1" => {
    "gitaly_address" => "tcp://LOAD_BALANCER_SERVER_ADDRESS:2305",
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})
```
Allow Gitaly to listen on a TCP port by editing /etc/gitlab/gitlab.rb
```
gitaly['listen_addr'] = '0.0.0.0:8075'
```
Configure the gitlab_shell['secret_token'] so that callbacks from Gitaly nodes during a git push are properly authenticated by editing /etc/gitlab/gitlab.rb:

You will need to replace GITLAB_SHELL_SECRET_TOKEN with the real secret.
```
gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'
```

Add Prometheus monitoring settings by editing /etc/gitlab/gitlab.rb.

You will need to replace:

PRAEFECT_HOST with the IP address or hostname of the Praefect node
GITALY_HOST with the IP address or hostname of each Gitaly node

prometheus['scrape_configs'] = [
  {
    'job_name' => 'praefect',
    'static_configs' => [
      'targets' => [
        'PRAEFECT_HOST:9652', # praefect-1
        'PRAEFECT_HOST:9652', # praefect-2
        'PRAEFECT_HOST:9652', # praefect-3
      ]
    ]
  },
  {
    'job_name' => 'praefect-gitaly',
    'static_configs' => [
      'targets' => [
        'GITALY_HOST:9236', # gitaly-1
        'GITALY_HOST:9236', # gitaly-2
        'GITALY_HOST:9236', # gitaly-3
      ]
    ]
  }
]

Save the changes to /etc/gitlab/gitlab.rb and reconfigure GitLab:
```
gitlab-ctl reconfigure
```
To ensure that Gitaly has updated its Prometheus listen address, restart Gitaly:
```
gitlab-ctl restart gitaly
```

Verify each gitlab-shell on each Gitaly instance can reach GitLab. On each Gitaly instance run:

/opt/gitlab/embedded/service/gitlab-shell/bin/check -config /opt/gitlab/embedded/service/gitlab-shell/config.yml

Verify that GitLab can reach Praefect:
```
gitlab-rake gitlab:gitaly:check
```
Update the Repository storage settings from Admin Area > Settings > Repository > Repository storage to make the newly configured Praefect cluster the storage location for new Git repositories.
- The default option is unchecked.
- The Praefect option is checked.
Verify everything is still working by creating a new project. Check the "Initialize repository with a README" box so that there is content in the repository that viewed. If the project is created, and you can see the README file, it works!

Grafana

Grafana is included with GitLab, and can be used to monitor your Praefect cluster. See Grafana Dashboard Service for detailed documentation.

To get started quickly:

SSH into the GitLab node and login as root:
```
sudo -i
```
Enable the Grafana login form by editing /etc/gitlab/gitlab.rb.
```
grafana['disable_login_form'] = false
```
Save the changes to /etc/gitlab/gitlab.rb and reconfigure GitLab:
```
gitlab-ctl reconfigure
```
Set the Grafana admin password. This command will prompt you to enter a new password:
```
gitlab-ctl set-grafana-password
```
In your web browser, open /-/grafana (e.g. https://gitlab.example.com/-/grafana) on your GitLab server.

Login using the password you set, and the username admin.
Go to Explore and query gitlab_build_info to verify that you are getting metrics from all your machines.

Congratulations! You've configured an observable highly available Praefect cluster.

Automatic failover and leader election

Praefect regularly checks the health of each backend Gitaly node. This information can be used to automatically failover to a new primary node if the current primary node is found to be unhealthy.

PostgreSQL (recommended): Enabled by default, and equivalent to: praefect['failover_election_strategy'] = sql. This configuration option will allow multiple Praefect nodes to coordinate via the PostgreSQL database to elect a primary Gitaly node. This configuration will cause Praefect nodes to elect a new primary, monitor its health, and elect a new primary if the current one has not been reachable in 10 seconds by a majority of the Praefect nodes.
Manual: Automatic failover is disabled. The primary node can be reconfigured in /etc/gitlab/gitlab.rb on the Praefect node. Modify the praefect['virtual_storages'] field by moving the primary = true to promote a different Gitaly node to primary. In the steps above, gitaly-1 was set to the primary. Requires praefect['failover_enabled'] = false in the configuration.
Memory: Enabled by setting praefect['failover_election_strategy'] = 'local' in /etc/gitlab/gitlab.rb on the Praefect node. If a sufficient number of health checks fail for the current primary backend Gitaly node, and new primary will be elected. Do not use with multiple Praefect nodes! Using with multiple Praefect nodes is likely to result in a split brain.

It is likely that we will implement support for Consul, and a cloud native strategy in the future.

Identifying Impact of a Primary Node Failure

When a primary Gitaly node fails, there is a chance of data loss. Data loss can occur if there were outstanding replication jobs the secondaries did not manage to process before the failure. The dataloss Praefect sub-command helps identify these cases by counting the number of dead replication jobs for each repository. This command must be executed on a Praefect node.

A time frame to search can be specified with -from and -to:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dataloss -from <rfc3339-time> -to <rfc3339-time>

If the time frame is not specified, dead replication jobs from the last six hours are counted:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dataloss

Failed replication jobs between [2020-01-02 00:00:00 +0000 UTC, 2020-01-02 06:00:00 +0000 UTC):
@hashed/fa/53/fa539965395b8382145f8370b34eab249cf610d2d6f2943c95b9b9d08a63d4a3.git: 2 jobs

To specify a time frame in UTC, run:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dataloss -from 2020-01-02T00:00:00+00:00 -to 2020-01-02T00:02:00+00:00

Checking repository checksums

To check a project's repository checksums across on all Gitaly nodes, the replicas Rake task can be run on the main GitLab node:

sudo gitlab-rake "gitlab:praefect:replicas[project_id]"

Backend Node Recovery

When a Praefect backend node fails and is no longer able to replicate changes, the backend node will start to drift from the primary. If that node eventually recovers, it will need to be reconciled with the current primary. The primary node is considered the single source of truth for the state of a shard. The Praefect reconcile sub-command allows for the manual reconciliation between a backend node and the current primary.

Run the following command on the Praefect server after all placeholders (<virtual-storage> and <target-storage>) have been replaced:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml reconcile -virtual <virtual-storage> -target <target-storage>

Replace the placeholder <virtual-storage> with the virtual storage containing the backend node storage to be checked.
Replace the placeholder <target-storage> with the backend storage name.

The command will return a list of repositories that were found to be inconsistent against the current primary. Each of these inconsistencies will also be logged with an accompanying replication job ID.

Migrating existing repositories to Praefect

If your GitLab instance already has repositories, these won't be migrated automatically.

Repositories may be moved from one storage location using the Repository API:

curl --request PUT --header "PRIVATE-TOKEN: <your_access_token>" --data "repository_storage=praefect" https://example.gitlab.com/api/v4/projects/123

Debugging Praefect

If you receive an error, check /var/log/gitlab/gitlab-rails/production.log.

Here are common errors and potential causes:

500 response code
- ActionView::Template::Error (7:permission denied)
  - praefect['auth_token'] and gitlab_rails['gitaly_token'] do not match on the GitLab server.
- Unable to save project. Error: 7:permission denied
  - Secret token in praefect['storage_nodes'] on GitLab server does not match the value in gitaly['auth_token'] on one or more Gitaly servers.
503 response code
- GRPC::Unavailable (14:failed to connect to all addresses)
  - GitLab was unable to reach Praefect.
- GRPC::Unavailable (14:all SubCons are in TransientFailure...)
  - Praefect cannot reach one or more of its child Gitaly nodes. Try running the Praefect connection checker to diagnose.