gitlab-org--gitlab-foss/doc/administration/gitaly/praefect.md

Praefect

NOTE: Note: Praefect is an experimental service, and for testing purposes only at this time.

Praefect is an optional reverse-proxy for Gitaly to manage a cluster of Gitaly nodes for high availability through replication. If a Gitaly node becomes unavailable, it will be possible to fail over to a warm Gitaly replica.

The first minimal version will support:

• Eventual consistency of the secondary replicas.
• Manual fail over from the primary to the secondary.

Follow the HA Gitaly epic for updates and roadmap.

Omnibus

Architecture

The most common architecture for Praefect is simplified in the diagram below:

graph TB
  GitLab --> Praefect;
  Praefect --> Gitaly-1;
  Praefect --> Gitaly-2;
  Praefect --> Gitaly-3;

Where GitLab is the collection of clients that can request Git operations. The Praefect node has threestorage nodes attached. Praefect itself doesn't store data, but connects to three Gitaly nodes, Gitaly-1, Gitaly-2, and Gitaly-3.

Praefect may be enabled on its own node or can be run on the GitLab server. In the example below we will use a separate server, but the optimal configuration for Praefect is still being determined.

Praefect will handle all Gitaly RPC requests to its child nodes. However, the child nodes will still need to communicate with the GitLab server via its internal API for authentication purposes.

Setup

In this setup guide we will start by configuring Praefect, then its child Gitaly nodes, and lastly the GitLab server configuration.

Secrets

We need to manage the following secrets and make them match across hosts:

1. 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.
2. PRAEFECT_EXTERNAL_TOKEN: repositories hosted on your Praefect cluster can only be accessed by Gitaly clients that carry this token.
3. 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

On the Praefect node we disable all other services, including Gitaly. We list each Gitaly node that will be connected to Praefect under praefect['storage_nodes'].

In the example below, the Gitaly nodes are named gitaly-N. Note that one node is designated as primary by setting the primary to true.

# /etc/gitlab/gitlab.rb on praefect server

# Avoid running unnecessary services on the Gitaly server
postgresql['enable'] = false
redis['enable'] = false
nginx['enable'] = false
prometheus['enable'] = false
unicorn['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false
gitaly['enable'] = false

Set up Praefect and its Gitaly nodes

In the example below, the Gitaly nodes are named gitaly-X. Note that one node is designated as primary, by setting the primary to true:

# /etc/gitlab/gitlab.rb on praefect server

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

praefect['enable'] = true

# Make Praefect accept connections on all network interfaces. You must use
# firewalls to restrict access to this address/port.
praefect['listen_addr'] = '0.0.0.0:2305'

# virtual_storage_name must match the same storage name given to praefect in git_data_dirs
praefect['virtual_storage_name'] = 'praefect'

# Replace PRAEFECT_EXTERNAL_TOKEN with a real secret
praefect['auth_token'] = 'PRAEFECT_EXTERNAL_TOKEN'

# Replace each instance of PRAEFECT_INTERNAL_TOKEN below with a real
# secret, distinct from PRAEFECT_EXTERNAL_TOKEN.
praefect['storage_nodes'] = {
  'gitaly-1' => {
    'address' => 'tcp://gitaly-1.internal:8075',
    'token'   => 'PRAEFECT_INTERNAL_TOKEN',
    'primary' => true
  },
  'gitaly-2' => {
    'address' => 'tcp://gitaly-2.internal:8075',
    'token'   => 'PRAEFECT_INTERNAL_TOKEN'
  },
  'gitaly-3' => {
    'address' => 'tcp://gitaly-3.internal:8075',
    'token'   => 'PRAEFECT_INTERNAL_TOKEN'
  }
}

Save the file and reconfigure Praefect.

Gitaly

Next we will configure each Gitaly server assigned to Praefect. Configuration for these is the same as a normal standalone Gitaly server, except that we use storage names and auth tokens from Praefect instead of GitLab.

Below is an example configuration for gitaly-1, the only difference for the other Gitaly nodes is the storage name under git_data_dirs.

Note that gitaly['auth_token'] matches the token value listed under praefect['storage_nodes'] on the Praefect node.

# /etc/gitlab/gitlab.rb on gitaly node inside praefect cluster

# Avoid running unnecessary services on the Gitaly server
postgresql['enable'] = false
redis['enable'] = false
nginx['enable'] = false
prometheus['enable'] = false
unicorn['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false

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

# Replace GITLAB_SHELL_SECRET_TOKEN below with real secret
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.
gitlab_rails['internal_api_url'] = 'https://gitlab.example.com'

# Replace PRAEFECT_INTERNAL_TOKEN below with a real secret.
gitaly['auth_token'] = 'PRAEFECT_INTERNAL_TOKEN'

# Make Gitaly accept connections on all network interfaces. You must use
# firewalls to restrict access to this address/port.
# Comment out following line if you only want to support TLS connections
gitaly['listen_addr'] = "0.0.0.0:8075"

git_data_dirs({
  "gitaly-1" => {
    "path" => "/var/opt/gitlab/git-data"
  }
})

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

GitLab

When Praefect is running, it should be exposed as a storage to GitLab. This is done through setting the git_data_dirs. Assuming the default storage is present, there should be two storages available to GitLab:

# /etc/gitlab/gitlab.rb on gitlab server

# Replace PRAEFECT_EXTERNAL_TOKEN below with real secret.
git_data_dirs({
  "default" => {
    "gitaly_address" => "tcp://gitaly.internal"
  },
  "praefect" => {
    "gitaly_address" => "tcp://praefect.internal:2305",
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

# Replace GITLAB_SHELL_SECRET_TOKEN below with real secret
gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'

Note that the storage name used is the same as the praefect['virtual_storage_name'] set on the Praefect node.

Restart GitLab using gitlab-ctl restart on the GitLab node.

Testing Praefect

To test Praefect, first set it as the default storage node for new projects using Admin Area > Settings > Repository > Repository storage. Next, create a new project and check the "Initialize repository with a README" box.

If you receive a 503 error, check /var/log/gitlab/gitlab-rails/production.log. A GRPC::Unavailable (14:failed to connect to all addresses) error indicates that GitLab was unable to connect to Praefect.