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Configure Gitaly Cluster

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Configure Gitaly Cluster using either:

Smaller GitLab installations may need only Gitaly itself.

NOTE: Gitaly Cluster is not yet supported in Kubernetes, Amazon ECS, or similar container environments. For more information, see epic 6127.

Requirements

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)

NOTE: Disk requirements apply to Gitaly nodes.

You should configure an odd number of Gitaly nodes so that transactions have a tie-breaker in case one of the Gitaly nodes fails in a mutating RPC call.

See the design document for implementation details.

NOTE: If not set in GitLab, feature flags are read as false from the console and Praefect uses their default value. The default value depends on the GitLab version.

Network latency and connectivity

Network latency for Gitaly Cluster should ideally be measurable in single-digit milliseconds. Latency is particularly important for:

  • Gitaly node health checks. Nodes must be able to respond within 1 second.
  • Reference transactions that enforce strong consistency. Lower latencies mean Gitaly nodes can agree on changes faster.

Achieving acceptable latency between Gitaly nodes:

  • On physical networks generally means high bandwidth, single location connections.
  • On the cloud generally means in the same region, including allowing cross availability zone replication. These links are designed for this type of synchronization. Latency of less than 2 ms should be sufficient for Gitaly Cluster.

If you can't provide low network latencies for replication (for example, between distant locations), consider Geo. For more information, see Comparison to Geo.

Gitaly Cluster components communicate with each other over many routes. Your firewall rules must allow the following for Gitaly Cluster to function properly:

From To Default port TLS port
GitLab Praefect load balancer 2305 3305
Praefect load balancer Praefect 2305 3305
Praefect Gitaly 8075 9999
Praefect GitLab (internal API) 80 443
Gitaly GitLab (internal API) 80 443
Gitaly Praefect load balancer 2305 3305
Gitaly Praefect 2305 3305
Gitaly Gitaly 8075 9999

NOTE: Gitaly does not directly connect to Praefect. However, requests from Gitaly to the Praefect load balancer may still be blocked unless firewalls on the Praefect nodes allow traffic from the Gitaly nodes.

Praefect database storage

The requirements are relatively low because the database contains only metadata of:

  • Where repositories are located.
  • Some queued work.

It depends on the number of repositories, but a good minimum is 5-10 GB, similar to the main GitLab application database.

Setup Instructions

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

  1. Preparation
  2. Configuring the Praefect database
  3. Configuring the Praefect proxy/router
  4. Configuring each Gitaly node (once for each Gitaly node)
  5. Configure the load balancer
  6. Updating the GitLab server configuration
  7. Configure Grafana

Preparation

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

Provision a PostgreSQL server. You should use the PostgreSQL that is shipped with the Linux package and use it to configure the PostgreSQL database. You can use an external PostgreSQL server (version 11 or newer) but you must set it up manually.

Prepare all your new nodes by installing GitLab. You need:

  • 1 PostgreSQL node
  • 1 PgBouncer node (optional)
  • At least 1 Praefect node (minimal storage required)
  • 3 Gitaly nodes (high CPU, high memory, fast storage)
  • 1 GitLab server

You also need the IP/host address for each node:

  1. PRAEFECT_LOADBALANCER_HOST: the IP/host address of Praefect load balancer
  2. POSTGRESQL_HOST: the IP/host address of the PostgreSQL server
  3. PGBOUNCER_HOST: the IP/host address of the PostgreSQL server
  4. PRAEFECT_HOST: the IP/host address of the Praefect server
  5. GITALY_HOST_*: the IP or host address of each Gitaly server
  6. GITLAB_HOST: the IP/host address of the GitLab server

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 enables you to replace these placeholder tokens with secure tokens as you complete the setup process.

  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 token 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.
  4. PRAEFECT_SQL_PASSWORD: this password is used by Praefect to connect to PostgreSQL.
  5. PRAEFECT_SQL_PASSWORD_HASH: the hash of password of the Praefect user. Use gitlab-ctl pg-password-md5 praefect to generate the hash. The command asks for the password for praefect user. Enter PRAEFECT_SQL_PASSWORD plaintext password. By default, Praefect uses praefect user, but you can change it.
  6. PGBOUNCER_SQL_PASSWORD_HASH: the hash of password of the PgBouncer user. PgBouncer uses this password to connect to PostgreSQL. For more details see bundled PgBouncer documentation.

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

NOTE: Linux package installations can use gitlab-secrets.json for GITLAB_SHELL_SECRET_TOKEN.

Customize time server setting

By default, Gitaly and Praefect nodes use the time server at pool.ntp.org for time synchronization checks. You can customize this setting by adding the following to gitlab.rb on each node:

  • gitaly['env'] = { "NTP_HOST" => "ntp.example.com" }, for Gitaly nodes.
  • praefect['env'] = { "NTP_HOST" => "ntp.example.com" }, for Praefect nodes.

PostgreSQL

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.

These instructions help set up a single PostgreSQL database, which creates a single point of failure. To avoid this, you can configure your own clustered PostgreSQL. Support for PostgreSQL replication and failover using the Linux package is proposed in epic 7814. Clustered database support for other databases (for example, Praefect and Geo databases) is proposed in issue 7292.

The following options are available:

Setting up PostgreSQL creates empty Praefect tables. For more information, see the relevant troubleshooting section.

Running GitLab and Praefect databases on the same server

The GitLab application database and the Praefect database can be run on the same server. However, Praefect should have its own database server when using PostgreSQL from the Linux package. If there is a failover, Praefect isn't aware and starts to fail as the database it's trying to use would either:

  • Be unavailable.
  • In read-only mode.

Manual database setup

To complete this section you need:

  • One Praefect node
  • One PostgreSQL node (version 11 or newer)
    • A PostgreSQL user with permissions to manage the database server

In this section, we configure the PostgreSQL database. This can be used for both external and Linux package-provided PostgreSQL server.

To run the following instructions, you can use the Praefect node, where psql is installed by the Linux package (/opt/gitlab/embedded/bin/psql). If you are using the Linux package-provided PostgreSQL you can use gitlab-psql on the PostgreSQL node instead:

  1. Create a new user praefect to be used by Praefect:

    CREATE ROLE praefect WITH LOGIN PASSWORD 'PRAEFECT_SQL_PASSWORD';

    Replace PRAEFECT_SQL_PASSWORD with the strong password you generated in the preparation step.

  2. Create a new database praefect_production that is owned by praefect user.

    CREATE DATABASE praefect_production WITH OWNER praefect ENCODING UTF8;

When using the Linux package-provided PgBouncer, you need to take the following additional steps. We strongly recommend using the PostgreSQL that is shipped with the Linux package as the backend. The following instructions only work on the Linux package-provided PostgreSQL:

  1. For the Linux package-provided PgBouncer, you need to use the hash of praefect password instead the of the actual password:

    ALTER ROLE praefect WITH PASSWORD 'md5<PRAEFECT_SQL_PASSWORD_HASH>';

    Replace <PRAEFECT_SQL_PASSWORD_HASH> with the hash of the password you generated in the preparation step. It is prefixed with md5 literal.

  2. The PgBouncer that is shipped with the Linux package is configured to use auth_query and uses pg_shadow_lookup function. You need to create this function in praefect_production database:

    CREATE OR REPLACE FUNCTION public.pg_shadow_lookup(in i_username text, out username text, out password text) RETURNS record AS $$
BEGIN
    SELECT usename, passwd FROM pg_catalog.pg_shadow
    WHERE usename = i_username INTO username, password;
    RETURN;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

REVOKE ALL ON FUNCTION public.pg_shadow_lookup(text) FROM public, pgbouncer;
GRANT EXECUTE ON FUNCTION public.pg_shadow_lookup(text) TO pgbouncer;

The database used by Praefect is now configured.

You can now configure Praefect to use the database:

praefect['configuration'] = {
   # ...
   database: {
      # ...
      host: POSTGRESQL_HOST,
      user: 'praefect',
      port: 5432,
      password: PRAEFECT_SQL_PASSWORD,
      dbname: 'praefect_production',
   }
}

If you see Praefect database errors after configuring PostgreSQL, see troubleshooting steps.

Reads distribution caching

Praefect performance can be improved by additionally configuring the session_pooled settings:

praefect['configuration'] = {
   # ...
   database: {
      # ...
      session_pooled: {
         # ...
         host: POSTGRESQL_HOST,
         port: 5432

         # Use the following to override parameters of direct database connection.
         # Comment out where the parameters are the same for both connections.
         user: 'praefect',
         password: PRAEFECT_SQL_PASSWORD,
         dbname: 'praefect_production',
         # sslmode: '...',
         # sslcert: '...',
         # sslkey: '...',
         # sslrootcert: '...',
      }
   }
}

When configured, this connection is automatically used for the SQL LISTEN feature and allows Praefect to receive notifications from PostgreSQL for cache invalidation.

Verify this feature is working by looking for the following log entry in the Praefect log:

reads distribution caching is enabled by configuration

Use PgBouncer

To reduce PostgreSQL resource consumption, you should set up and configure PgBouncer in front of the PostgreSQL instance. However, PgBouncer isn't required because Praefect makes a low number of connections. If you choose to use PgBouncer, you can use the same PgBouncer instance for both the GitLab application database and the Praefect database.

To configure PgBouncer in front of the PostgreSQL instance, you must point Praefect to PgBouncer by setting database parameters on Praefect configuration:

praefect['configuration'] = {
   # ...
   database: {
      # ...
      host: PGBOUNCER_HOST,
      port: 6432,
      user: 'praefect',
      password: PRAEFECT_SQL_PASSWORD,
      dbname: 'praefect_production',
      # sslmode: '...',
      # sslcert: '...',
      # sslkey: '...',
      # sslrootcert: '...',
   }
}

Praefect requires an additional connection to the PostgreSQL that supports the LISTEN feature. With PgBouncer this feature is only available with session pool mode (pool_mode = session). It is not supported in transaction pool mode (pool_mode = transaction).

To configure the additional connection, you must either:

  • Configure a new PgBouncer database that uses to the same PostgreSQL database endpoint, but with different pool mode (pool_mode = session).
  • Connect Praefect directly to PostgreSQL and bypass PgBouncer.

Configure a new PgBouncer database with pool_mode = session

You should use PgBouncer with session pool mode. You can use the bundled PgBouncer or use an external PgBouncer and configure it manually.

The following example uses the bundled PgBouncer and sets up two separate connection pools on PostgreSQL host, one in session pool mode and the other in transaction pool mode. For this example to work, you need to prepare PostgreSQL server as documented in the setup instructions:

pgbouncer['databases'] = {
  # Other database configuration including gitlabhq_production
  ...

  praefect_production: {
    host: POSTGRESQL_HOST,
    # Use `pgbouncer` user to connect to database backend.
    user: 'pgbouncer',
    password: PGBOUNCER_SQL_PASSWORD_HASH,
    pool_mode: 'transaction'
  },
  praefect_production_direct: {
    host: POSTGRESQL_HOST,
    # Use `pgbouncer` user to connect to database backend.
    user: 'pgbouncer',
    password: PGBOUNCER_SQL_PASSWORD_HASH,
    dbname: 'praefect_production',
    pool_mode: 'session'
  },

  ...
}

# Allow the praefect user to connect to PgBouncer
pgbouncer['users'] = {
  'praefect': {
    'password': PRAEFECT_SQL_PASSWORD_HASH,
  }
}

Both praefect_production and praefect_production_direct use the same database endpoint (praefect_production), but with different pool modes. This translates to the following databases section of PgBouncer:

[databases]
praefect_production = host=POSTGRESQL_HOST auth_user=pgbouncer pool_mode=transaction
praefect_production_direct = host=POSTGRESQL_HOST auth_user=pgbouncer dbname=praefect_production pool_mode=session

Now you can configure Praefect to use PgBouncer for both connections:

praefect['configuration'] = {
   # ...
   database: {
      # ...
      host: PGBOUNCER_HOST,
      port: 6432,
      user: 'praefect',
      # `PRAEFECT_SQL_PASSWORD` is the plain-text password of
      # Praefect user. Not to be confused with `PRAEFECT_SQL_PASSWORD_HASH`.
      password: PRAEFECT_SQL_PASSWORD,
      dbname: 'praefect_production',
      session_pooled: {
         # ...
         dbname: 'praefect_production_direct',
         # There is no need to repeat the following. Parameters of direct
         # database connection will fall back to the values above.
         #
         # host: PGBOUNCER_HOST,
         # port: 6432,
         # user: 'praefect',
         # password: PRAEFECT_SQL_PASSWORD,
      },
   },
}

With this configuration, Praefect uses PgBouncer for both connection types.

NOTE: Linux package installations handle the authentication requirements (using auth_query), but if you are preparing your databases manually and configuring an external PgBouncer, you must include praefect user and its password in the file used by PgBouncer. For example, userlist.txt if the auth_file configuration option is set. For more details, consult the PgBouncer documentation.

Configure Praefect to connect directly to PostgreSQL

As an alternative to configuring PgBouncer with session pool mode, Praefect can be configured to use different connection parameters for direct access to PostgreSQL. This connection supports the LISTEN feature.

An example of Praefect configuration that bypasses PgBouncer and directly connects to PostgreSQL:

praefect['configuration'] = {
   # ...
   database: {
      # ...
      session_pooled: {
         # ...
         host: POSTGRESQL_HOST,
         port: 5432,

         # Use the following to override parameters of direct database connection.
         # Comment out where the parameters are the same for both connections.
         #
         user: 'praefect',
         password: PRAEFECT_SQL_PASSWORD,
         dbname: 'praefect_production',
         # sslmode: '...',
         # sslcert: '...',
         # sslkey: '...',
         # sslrootcert: '...',
      },
   },
}

Praefect

If there are multiple Praefect nodes:

  1. Designate one node as the deploy node, and configure it using the following steps.
  2. Complete the following steps for each additional node.

To complete this section you need a configured PostgreSQL server, including:

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

On the Praefect node:

  1. Disable all other services by editing /etc/gitlab/gitlab.rb:
# Avoid running unnecessary services on the Praefect server
gitaly['enable'] = false
postgresql['enable'] = false
redis['enable'] = false
nginx['enable'] = false
puma['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false
prometheus['enable'] = false
alertmanager['enable'] = false
grafana['enable'] = false
gitlab_exporter['enable'] = false
gitlab_kas['enable'] = false

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

# Prevent database migrations from running on upgrade automatically
praefect['auto_migrate'] = false
gitlab_rails['auto_migrate'] = false

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

    praefect['configuration'] = {
   # ...
   listen_addr: '0.0.0.0:2305',
}

  2. Configure Prometheus metrics by editing /etc/gitlab/gitlab.rb:

    praefect['configuration'] = {
   # ...
   #
   # Enable Prometheus metrics access to Praefect. You must use firewalls
   # to restrict access to this address/port.
   # The default metrics endpoint is /metrics
   prometheus_listen_addr: '0.0.0.0:9652',
   # Some metrics run queries against the database. Enabling separate database metrics allows
   # these metrics to be collected when the metrics are
   # scraped on a separate /db_metrics endpoint.
   prometheus_exclude_database_from_default_metrics: true,
}

  3. Configure a strong authentication token for Praefect by editing /etc/gitlab/gitlab.rb, which is needed by clients outside the cluster (like GitLab Shell) to communicate with the Praefect cluster:

    praefect['configuration'] = {
   # ...
   auth: {
      # ...
      token: 'PRAEFECT_EXTERNAL_TOKEN',
   },
}

  4. Configure Praefect to connect to the PostgreSQL database. We highly recommend using PgBouncer as well.

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

    praefect['configuration'] = {
   # ...
   database: {
      # ...
      #
      # Connect to PostgreSQL using a TLS client certificate
      # sslcert: '/path/to/client-cert',
      # sslkey: '/path/to/client-key',
      #
      # Trust a custom certificate authority
      # sslrootcert: '/path/to/rootcert',
   },
}

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

    praefect['configuration'] = {
   # ...
   database: {
      # ...
      # sslmode: 'disable',
   },
}

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

    The virtual storage's name must match the configured storage name in GitLab configuration. In a later step, we configure the storage name as default so we use default here as well. This cluster has three Gitaly nodes gitaly-1, gitaly-2, and gitaly-3, which are intended to be replicas of each other.

    WARNING: If you have data on an already existing storage called default, you should configure the virtual storage with another name and migrate the data to the Gitaly Cluster storage afterwards.

    Replace PRAEFECT_INTERNAL_TOKEN with a strong secret, which is 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 or 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: When adding additional Gitaly nodes to a virtual storage, all storage names in that virtual storage must be unique. Additionally, all Gitaly node addresses referenced in the Praefect configuration must be unique.

    # Name of storage hash must match storage name in git_data_dirs on GitLab
# server ('default') and in gitaly['configuration'][:storage][INDEX][:name] on Gitaly nodes ('gitaly-1')
praefect['configuration'] = {
   # ...
   virtual_storage: [
      {
         # ...
         name: 'default',
         node: [
            {
               storage: 'gitaly-1',
               address: 'tcp://GITALY_HOST_1:8075',
               token: 'PRAEFECT_INTERNAL_TOKEN'
            },
            {
               storage: 'gitaly-2',
               address: 'tcp://GITALY_HOST_2:8075',
               token: 'PRAEFECT_INTERNAL_TOKEN'
            },
            {
               storage: 'gitaly-3',
               address: 'tcp://GITALY_HOST_3:8075',
               token: 'PRAEFECT_INTERNAL_TOKEN'
            },
         ],
      },
   ],
}

  6. Save the changes to /etc/gitlab/gitlab.rb and reconfigure Praefect:

    gitlab-ctl reconfigure

  7. For:

    • The "deploy node":

      1. Enable Praefect database auto-migration again by setting praefect['auto_migrate'] = true in /etc/gitlab/gitlab.rb.

      2. To ensure database migrations are only run during reconfigure and not automatically on upgrade, run:

        sudo touch /etc/gitlab/skip-auto-reconfigure

    • The other nodes, you can leave the settings as they are. Though /etc/gitlab/skip-auto-reconfigure isn't required, you may want to set it to prevent GitLab running reconfigure automatically when running commands such as apt-get update. This way any additional configuration changes can be done and then reconfigure can be run manually.

  8. Save the changes to /etc/gitlab/gitlab.rb and reconfigure Praefect:

    gitlab-ctl reconfigure

  9. To ensure that Praefect has updated its Prometheus listen address, restart Praefect:

    gitlab-ctl restart praefect

  10. 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.

Enable TLS support

Praefect supports TLS encryption. To communicate with a Praefect instance that listens for secure connections, you must:

  • Ensure Gitaly is configured for TLS and use a tls:// URL scheme in the gitaly_address of the corresponding storage entry in the GitLab configuration.
  • Bring your own certificates because this isn't provided automatically. The certificate corresponding to each Praefect server must be installed on that Praefect server.

Additionally the certificate, or its certificate authority, must be installed on all Gitaly servers and on all Praefect clients that communicate with it following the procedure described in GitLab custom certificate configuration (and repeated below).

Note the following:

  • The certificate must specify the address you use to access the Praefect server. You must add the hostname or IP address as a Subject Alternative Name to the certificate.

  • When running Praefect sub-commands such as dial-nodes and list-untracked-repositories from the command line with Gitaly TLS enabled, you must set the SSL_CERT_DIR or SSL_CERT_FILE environment variable so that the Gitaly certificate is trusted. For example:

    sudo SSL_CERT_DIR=/etc/gitlab/trusted-certs /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dial-nodes

  • You can configure Praefect servers with both an unencrypted listening address listen_addr and an encrypted listening address tls_listen_addr at the same time. This allows you to do a gradual transition from unencrypted to encrypted traffic, if necessary.

    To disable the unencrypted listener, set:

    praefect['configuration'] = {
  # ...
  listen_addr: nil,
}

Configure Praefect with TLS.

For Linux package installations:

  1. Create certificates for Praefect servers.

  2. On the Praefect servers, create the /etc/gitlab/ssl directory and copy your key and certificate there:

    sudo mkdir -p /etc/gitlab/ssl
sudo chmod 755 /etc/gitlab/ssl
sudo cp key.pem cert.pem /etc/gitlab/ssl/
sudo chmod 644 key.pem cert.pem

  3. Edit /etc/gitlab/gitlab.rb and add:

    praefect['configuration'] = {
   # ...
   tls_listen_addr: '0.0.0.0:3305',
   tls: {
      # ...
      certificate_path: '/etc/gitlab/ssl/cert.pem',
      key_path: '/etc/gitlab/ssl/key.pem',
   },
}

  4. Save the file and reconfigure.

  5. On the Praefect clients (including each Gitaly server), copy the certificates, or their certificate authority, into /etc/gitlab/trusted-certs:

    sudo cp cert.pem /etc/gitlab/trusted-certs/

  6. On the Praefect clients (except Gitaly servers), edit git_data_dirs in /etc/gitlab/gitlab.rb as follows:

    git_data_dirs({
  "default" => {
    "gitaly_address" => 'tls://PRAEFECT_LOADBALANCER_HOST:3305',
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

  7. Save the file and reconfigure GitLab.

For self-compiled installations:

  1. Create certificates for Praefect servers.

  2. On the Praefect servers, create the /etc/gitlab/ssl directory and copy your key and certificate there:

    sudo mkdir -p /etc/gitlab/ssl
sudo chmod 755 /etc/gitlab/ssl
sudo cp key.pem cert.pem /etc/gitlab/ssl/
sudo chmod 644 key.pem cert.pem

  3. On the Praefect clients (including each Gitaly server), copy the certificates, or their certificate authority, into the system trusted certificates:

    sudo cp cert.pem /usr/local/share/ca-certificates/praefect.crt
sudo update-ca-certificates

  4. On the Praefect clients (except Gitaly servers), edit storages in /home/git/gitlab/config/gitlab.yml as follows:

    gitlab:
  repositories:
    storages:
      default:
        gitaly_address: tls://PRAEFECT_LOADBALANCER_HOST:3305

  5. Save the file and restart GitLab.

  6. Copy all Praefect server certificates, or their certificate authority, to the system trusted certificates on each Gitaly server so the Praefect server trusts the certificate when called by Gitaly servers:

    sudo cp cert.pem /usr/local/share/ca-certificates/praefect.crt
sudo update-ca-certificates

  7. Edit /home/git/praefect/config.toml and add:

    tls_listen_addr = '0.0.0.0:3305'

[tls]
certificate_path = '/etc/gitlab/ssl/cert.pem'
key_path = '/etc/gitlab/ssl/key.pem'

  8. Save the file and restart GitLab.

Service discovery

Prerequisites:

  • A DNS server.

GitLab uses service discovery to retrieve a list of Praefect hosts. Service discovery involves periodic checks of a DNS A or AAAA record, with the IPs retrieved from the record serving as the addresses of the target nodes. Praefect does not support service discovery by SRV record.

By default, the minimum time between checks is 5 minutes, regardless of the records' TTLs. Praefect does not support customizing this interval. When clients receive an update, they:

  • Establish new connections to the new IP addresses.
  • Keep existing connections to intact IP addresses.
  • Drop connections to removed IP addresses.

In-flight requests on to-be-removed connections are still handled until they finish. Workhorse has a 10-minute timeout, while other clients do not specify a graceful timeout.

The DNS server should return all IP addresses instead of load-balancing itself. Clients can distribute requests to IP addresses in a round-robin fashion.

Before updating client configuration, ensure that DNS service discovery works correctly. It should return the list of IP addresses correctly. dig is a good tool to use to verify.

❯ dig A praefect.service.consul @127.0.0.1

; <<>> DiG 9.10.6 <<>> A praefect.service.consul @127.0.0.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29210
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;praefect.service.consul.                     IN      A

;; ANSWER SECTION:
praefect.service.consul.              0       IN      A       10.0.0.3
praefect.service.consul.              0       IN      A       10.0.0.2
praefect.service.consul.              0       IN      A       10.0.0.1

;; Query time: 0 msec
;; SERVER: ::1#53(::1)
;; WHEN: Wed Dec 14 12:53:58 +07 2022
;; MSG SIZE  rcvd: 86
Configure service discovery

By default, Praefect delegates DNS resolution to the operating system. In such cases, the Gitaly address can be set in either of these formats:

  • dns:[host]:[port]
  • dns:///[host]:[port] (note the three slashes)

You can also appoint an authoritative name server by setting it in this format:

  • dns://[authority_host]:[authority_port]/[host]:[port]

::Tabs

:::TabTitle Linux package (Omnibus)

  1. Add the IP address for each Praefect node to the DNS service discovery address.

  2. On the Praefect clients (except Gitaly servers), edit git_data_dirs in /etc/gitlab/gitlab.rb as follows. Replace PRAEFECT_SERVICE_DISCOVERY_ADDRESS with Praefect service discovery address, such as praefect.service.consul.

    git_data_dirs({
  "default" => {
    "gitaly_address" => 'dns:PRAEFECT_SERVICE_DISCOVERY_ADDRESS:2305',
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

  3. Save the file and reconfigure GitLab.

:::TabTitle Self-compiled (source)

  1. Install a DNS service discovery service. Register all Praefect nodes with the service.

  2. On the Praefect clients (except Gitaly servers), edit storages in /home/git/gitlab/config/gitlab.yml as follows:

    gitlab:
  repositories:
    storages:
      default:
        gitaly_address: dns:PRAEFECT_SERVICE_DISCOVERY_ADDRESS:2305

  3. Save the file and restart GitLab.

::EndTabs

Configure service discovery with Consul

If you already have a Consul server in your architecture then you can add a Consul agent on each Praefect node and register the praefect service to it. This registers each node's IP address to praefect.service.consul so it can be found by service discovery.

Prerequisites:

  • One or more Consul servers to keep track of the Consul agents.

  1. On each Praefect server, add the following to your /etc/gitlab/gitlab.rb:

    consul['enable'] = true
praefect['consul_service_name'] = 'praefect'

# The following must also be added until this issue is addressed:
# https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/8321
consul['monitoring_service_discovery'] = true
praefect['configuration'] = {
  # ...
  #
  prometheus_listen_addr: '0.0.0.0:9652',
}

  2. Save the file and reconfigure GitLab.

  3. Repeat the above steps on each Praefect server to use with service discovery.

  4. On the Praefect clients (except Gitaly servers), edit git_data_dirs in /etc/gitlab/gitlab.rb as follows. Replace CONSUL_SERVER with the IP or address of a Consul server. The default Consul DNS port is 8600.

    git_data_dirs({
  "default" => {
    "gitaly_address" => 'dns://CONSUL_SERVER:8600/praefect.service.consul:2305',
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

  5. Use dig from the Praefect clients to confirm that each IP address has been registered to praefect.service.consul with dig A praefect.service.consul @CONSUL_SERVER -p 8600. Replace CONSUL_SERVER with the value configured above and all Praefect node IP addresses should be present in the output.

  6. Save the file and reconfigure GitLab.

Gitaly

NOTE: Complete these steps for each Gitaly node.

To complete this section you 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 standard 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['configuration'][:auth][:token] configured in this section must match the token value under praefect['configuration'][:virtual_storage][<index>][:node][<index>][:token] on the Praefect node. This value was set in the previous section. This document uses the placeholder PRAEFECT_INTERNAL_TOKEN throughout.
  • The physical storage names in gitaly['configuration'][:storage] configured in this section must match the physical storage names under praefect['configuration'][:virtual_storage] on the Praefect node. This was set in the previous section. This document uses gitaly-1, gitaly-2, and gitaly-3 as physical storage names.

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

  1. SSH into the Gitaly node and login as root:

    sudo -i

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

    # Disable all other services on the Gitaly 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
gitlab_kas['enable'] = false

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

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

# Disable database migrations to prevent database connections during 'gitlab-ctl reconfigure'
gitlab_rails['auto_migrate'] = false

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

    gitaly['configuration'] = {
   # ...
   #
   # Make Gitaly accept connections on all network interfaces.
   # Use firewalls to restrict access to this address/port.
   listen_addr: '0.0.0.0:8075',
   # Enable Prometheus metrics access to Gitaly. You must use firewalls
   # to restrict access to this address/port.
   prometheus_listen_addr: '0.0.0.0:9236',
}

  4. Configure a strong auth_token for Gitaly by editing /etc/gitlab/gitlab.rb, which is needed by clients to communicate with this Gitaly nodes. Typically, this token is the same for all Gitaly nodes.

    gitaly['configuration'] = {
   # ...
   auth: {
      # ...
      token: 'PRAEFECT_INTERNAL_TOKEN',
   },
}

  5. Configure the GitLab Shell secret token, which is needed for git push operations. Either:

    • Method 1:

      1. Copy /etc/gitlab/gitlab-secrets.json from the Gitaly client to same path on the Gitaly servers and any other Gitaly clients.
      2. Reconfigure GitLab on Gitaly servers.

    • Method 2:

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

      2. Replace GITLAB_SHELL_SECRET_TOKEN with the real secret.

        gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'

  6. Configure an internal_api_url, which is also needed for git push operations:

    # 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://gitlab.example.com', 'http://10.0.2.2'
gitlab_rails['internal_api_url'] = 'https://gitlab.example.com'

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

    gitaly['configuration'] = {
   # ...
   storage: [
     # Replace with appropriate name for each Gitaly nodes.
     {
       name: 'gitaly-1',
       path: '/var/opt/gitlab/git-data/repositories',
     },
   ],
}

  8. Save the changes to /etc/gitlab/gitlab.rb and reconfigure Gitaly:

    gitlab-ctl reconfigure

  9. 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, run the Praefect connection checker to verify Praefect can connect to all Gitaly servers in the Praefect configuration.

  1. SSH into each 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 fault-tolerant 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.

NOTE: The load balancer must be configured to accept traffic from the Gitaly nodes in addition to the GitLab nodes.

We hope that if you're managing fault-tolerant 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 outlines what ports and protocols you need configure.

NOTE: You should use the equivalent of HAProxy leastconn load-balancing strategy because long-running operations (for example, clones) keep some connections open for extended periods.

LB Port Backend Port Protocol
2305 2305 TCP

GitLab

To complete this section you need:

The Praefect cluster needs to be exposed as a storage location to the GitLab application, which 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['configuration'][:virtual_storage] on the Praefect nodes. This was set in the Praefect section of this guide. This document uses default as the Praefect storage name.

  1. SSH into the GitLab node and login as root:

    sudo -i

  2. Configure the external_url so that files could be served by GitLab by proper endpoint access by editing /etc/gitlab/gitlab.rb:

    You need to replace GITLAB_SERVER_URL with the real external facing URL on which current GitLab instance is serving:

    external_url 'GITLAB_SERVER_URL'

  3. Disable the default Gitaly service running on the GitLab host. It isn't needed because GitLab connects to the configured cluster.

    WARNING: If you have existing data stored on the default Gitaly storage, you should migrate the data to your Gitaly Cluster storage first.

    gitaly['enable'] = false

  4. Add the Praefect cluster as a storage location by editing /etc/gitlab/gitlab.rb.

    You need to replace:

    • PRAEFECT_LOADBALANCER_HOST with the IP address or hostname of the load balancer.
    • PRAEFECT_EXTERNAL_TOKEN with the real secret

    If you are using TLS:

    • The gitaly_address should begin with tls:// instead.
    • The port should be changed to 3305.
    git_data_dirs({
  "default" => {
    "gitaly_address" => "tcp://PRAEFECT_LOADBALANCER_HOST:2305",
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

  5. Configure the GitLab Shell secret token so that callbacks from Gitaly nodes during a git push are properly authenticated. Either:

    • Method 1:

      1. Copy /etc/gitlab/gitlab-secrets.json from the Gitaly client to same path on the Gitaly servers and any other Gitaly clients.
      2. Reconfigure GitLab on Gitaly servers.

    • Method 2:

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

      2. Replace GITLAB_SHELL_SECRET_TOKEN with the real secret.

        gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'

  6. Add Prometheus monitoring settings by editing /etc/gitlab/gitlab.rb. If Prometheus is enabled on a different node, make edits on that node instead.

    You 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_1:9236', # gitaly-1
        'GITALY_HOST_2:9236', # gitaly-2
        'GITALY_HOST_3:9236', # gitaly-3
      ]
    ]
  }
]

  7. Save the changes to /etc/gitlab/gitlab.rb and reconfigure GitLab:

    gitlab-ctl reconfigure

  8. Verify on each Gitaly node the Git Hooks can reach GitLab. On each Gitaly node run:

    • For GitLab 15.3 and later, run sudo /opt/gitlab/embedded/bin/gitaly check /var/opt/gitlab/gitaly/config.toml.
    • For GitLab 15.2 and earlier, run sudo /opt/gitlab/embedded/bin/gitaly-hooks check /var/opt/gitlab/gitaly/config.toml.

  9. Verify that GitLab can reach Praefect:

    gitlab-rake gitlab:gitaly:check

  10. Check that the Praefect storage is configured to store new repositories:

    1. On the left sidebar, at the bottom, select Admin Area.
    2. On the left sidebar, select Settings > Repository.
    3. Expand the Repository storage section.

    Following this guide, the default storage should have weight 100 to store all new repositories.

  11. Verify everything is 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!

Use TCP for existing GitLab instances

When adding Gitaly Cluster to an existing Gitaly instance, the existing Gitaly storage must be listening on TCP/TLS. If gitaly_address is not specified, then a Unix socket is used, which prevents the communication with the cluster.

For example:

git_data_dirs({
  'default' => { 'gitaly_address' => 'tcp://old-gitaly.internal:8075' },
  'cluster' => {
    'gitaly_address' => 'tls://<PRAEFECT_LOADBALANCER_HOST>:3305',
    'gitaly_token' => '<praefect_external_token>'
  }
})

See Mixed Configuration for further information on running multiple Gitaly storages.

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:

  1. SSH into the GitLab node (or whichever node has Grafana enabled) and login as root:

    sudo -i

  2. Enable the Grafana login form by editing /etc/gitlab/gitlab.rb.

    grafana['disable_login_form'] = false

  3. Save the changes to /etc/gitlab/gitlab.rb and reconfigure GitLab:

    gitlab-ctl reconfigure

  4. Set the Grafana administrator password. This command prompts you to enter a new password:

    gitlab-ctl set-grafana-password

  5. In your web browser, open /-/grafana (such as https://gitlab.example.com/-/grafana) on your GitLab server.

    Login using the password you set, and the username admin.

  6. 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 fault-tolerant Praefect cluster.

Configure replication factor

Praefect supports configuring a replication factor on a per-repository basis, by assigning specific storage nodes to host a repository.

WARNING: Configurable replication factors requires repository-specific primary nodes.

Praefect does not store the actual replication factor, but assigns enough storages to host the repository so the desired replication factor is met. If a storage node is later removed from the virtual storage, the replication factor of repositories assigned to the storage is decreased accordingly.

You can configure either:

  • A default replication factor for each virtual storage that is applied to newly created repositories.
  • A replication factor for an existing repository with the set-replication-factor subcommand.

Configure default replication factor

If default_replication_factor is unset, the repositories are always replicated on every storage node defined in virtual_storages. If a new storage node is introduced to the virtual storage, both new and existing repositories are replicated to the node automatically.

For large Gitaly Cluster deployments with many storage nodes, replicating a repository to every storage node is often not sensible and can cause problems. A replication factor of 3 is usually sufficient, which means replicate repositories to three storages even if more are available. Higher replication factors increase the pressure on the primary storage.

To configure a default replication factor, add configuration to the /etc/gitlab/gitlab.rb file:

praefect['configuration'] = {
   # ...
   virtual_storage: [
      {
         # ...
         name: 'default',
         default_replication_factor: 3,
      },
   ],
}

Configure replication factor for existing repositories

The set-replication-factor subcommand automatically assigns or unassigns random storage nodes as necessary to reach the desired replication factor. The repository's primary node is always assigned first and is never unassigned.

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml set-replication-factor -virtual-storage <virtual-storage> -repository <relative-path> -replication-factor <replication-factor>
  • -virtual-storage is the virtual storage the repository is located in.
  • -repository is the repository's relative path in the storage.
  • -replication-factor is the desired replication factor of the repository. The minimum value is 1, as the primary needs a copy of the repository. The maximum replication factor is the number of storages in the virtual storage.

On success, the assigned host storages are printed. For example:

$ sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml set-replication-factor -virtual-storage default -repository @hashed/3f/db/3fdba35f04dc8c462986c992bcf875546257113072a909c162f7e470e581e278.git -replication-factor 2

current assignments: gitaly-1, gitaly-2

Repository storage recommendations

The size of the required storage can vary between instances and depends on the set replication factor. You might want to include implementing repository storage redundancy.

For a replication factor:

  • Of 1: Gitaly and Gitaly Cluster have roughly the same storage requirements.
  • More than 1: The amount of required storage is used space * replication factor. used space should include any planned future growth.

Repository verification

Praefect stores metadata about the repositories in a database. If the repositories are modified on disk without going through Praefect, the metadata can become inaccurate. For example if a Gitaly node is rebuilt, rather than being replaced with a new node, repository verification ensures this is detected.

The metadata is used for replication and routing decisions, so any inaccuracies may cause problems. Praefect contains a background worker that periodically verifies the metadata against the actual state on the disks. The worker:

  1. Picks up a batch of replicas to verify on healthy storages. The replicas are either unverified or have exceeded the configured verification interval. Replicas that have never been verified are prioritized, followed by the other replicas ordered by longest time since the last successful verification.
  2. Checks whether the replicas exist on their respective storages. If the:
    • Replica exists, update its last successful verification time.
    • Replica doesn't exist, remove its metadata record.
    • Check failed, the replica is picked up for verification again when the next worker dequeues more work.

The worker acquires an exclusive verification lease on each of the replicas it is about to verify. This avoids multiple workers from verifying the same replica concurrently. The worker releases the leases when it has completed its check. If workers are terminated for some reason without releasing the lease, Praefect contains a background goroutine that releases stale leases every 10 seconds.

The worker logs each of the metadata removals prior to executing them. The perform_deletions key indicates whether the invalid metadata records are actually deleted or not. For example:

{
  "level": "info",
  "msg": "removing metadata records of non-existent replicas",
  "perform_deletions": false,
  "replicas": {
    "default": {
      "@hashed/6b/86/6b86b273ff34fce19d6b804eff5a3f5747ada4eaa22f1d49c01e52ddb7875b4b.git": [
        "praefect-internal-0"
      ]
    }
  }
}

Configure the verification worker

The worker is enabled by default and verifies the metadata records every seven days. The verification interval is configurable with any valid Go duration string.

To verify the metadata every three days:

praefect['configuration'] = {
   # ...
   background_verification: {
      # ...
      verification_interval: '72h',
   },
}

Values of 0 and below disable the background verifier.

praefect['configuration'] = {
   # ...
   background_verification: {
      # ...
      verification_interval: '0',
   },
}

Enable deletions

WARNING: Deletions were disabled by default prior to GitLab 15.9 due to a race condition with repository renames that can cause incorrect deletions, which is especially prominent in Geo instances as Geo performs more renames than instances without Geo. In GitLab 15.0 to 15.5, you should enable deletions only if the gitaly_praefect_generated_replica_paths feature flag is enabled. The feature flag was removed in GitLab 15.6 making deletions always safe to enable.

By default, the worker deletes invalid metadata records. It also logs the deleted records and outputs Prometheus metrics.

You can disable deleting invalid metadata records with:

praefect['configuration'] = {
   # ...
   background_verification: {
      # ...
      delete_invalid_records: false,
   },
}

Prioritize verification manually

You can prioritize verification of some replicas ahead of their next scheduled verification time. This might be needed after a disk failure, for example, when the administrator knows that the disk contents may have changed. Praefect would eventually verify the replicas again, but users may encounter errors in the meantime.

To manually prioritize reverification of some replicas, use the praefect verify subcommand. The subcommand marks replicas as unverified. Unverified replicas are prioritized by the background verification worker. The verification worker must be enabled for the replicas to be verified.

Prioritize verifying the replicas of a specific repository:

sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml verify -repository-id=<repository-id>

Prioritize verifying all replicas stored on a virtual storage:

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

Prioritize verifying all replicas stored on a storage:

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

The output includes the number of replicas that were marked unverified.

Automatic failover and primary election strategies

Praefect regularly checks the health of each Gitaly node, which is used to automatically fail over to a newly-elected primary Gitaly node if the current primary node is found to be unhealthy.

Repository-specific primary nodes is the only available election strategy.

Repository-specific primary nodes

Gitaly Cluster elects a primary Gitaly node separately for each repository. Combined with configurable replication factors, you can horizontally scale storage capacity and distribute write load across Gitaly nodes.

Primary elections are run lazily. Praefect doesn't immediately elect a new primary node if the current one is unhealthy. A new primary is elected if a request must be served while the current primary is unavailable.

A valid primary node candidate is a Gitaly node that:

  • Is healthy. A Gitaly node is considered healthy if >=50% Praefect nodes have successfully health checked the Gitaly node in the previous ten seconds.
  • Has a fully up to date copy of the repository.

If there are multiple primary node candidates, Praefect:

  • Picks one of them randomly.
  • Prioritizes promoting a Gitaly node that is assigned to host the repository. If there are no assigned Gitaly nodes to elect as the primary, Praefect may temporarily elect an unassigned one. The unassigned primary is demoted in favor of an assigned one when one becomes available.

If there are no valid primary candidates for a repository:

  • The unhealthy primary node is demoted and the repository is left without a primary node.
  • Operations that require a primary node fail until a primary is successfully elected.