kotovalexarian-likes-gitlab/gitlab-org--gitlab-foss

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Praefect: High Availability

NOTE: Note: Praefect is an experimental service, and data loss is likely.

Praefect is an optional reverse-proxy for Gitaly to manage a cluster of Gitaly nodes for high availability. Initially, high availability be implemented through asynchronous 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.
Automatic fail over from the primary to the secondary.
Reporting of possible data loss if replication queue is non empty.

Follow the HA Gitaly epic for updates and roadmap.

Requirements for configuring Gitaly for High Availability

NOTE: Note: this reference architecture is not highly available because Praefect is a single point of failure.

The minimal alpha reference architecture additionally requires:

1 Praefect node
1 PostgreSQL server (PostgreSQL 9.6 or newer)
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)
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 9.6 or newer). Configuration through the GitLab Omnibus 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)

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

POSTGRESQL_SERVER_ADDRESS: the IP/host address of the PostgreSQL server
PRAEFECT_SERVER_ADDRESS: the IP/host address of the Praefect server
GITALY_SERVER_ADDRESS: the IP/host address of each Gitaly node

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: don't reuse the GitLab application database for the Praefect database.

To complete this section you will need:

1 Praefect node
1 PostgreSQL server (PostgreSQL 9.6 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 GitLab Omnibus.

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
unicorn['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:

# Make Praefect accept connections on all network interfaces.
# Use firewalls to restrict access to this address/port.
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 cluster named praefect. 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 to allow for automatic failover.
```
# 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'] = {
  'praefect' => {
    '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
```
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.

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
prometheus['enable'] = false
grafana['enable'] = false
unicorn['enable'] = false
sidekiq['enable'] = false
gitlab_workhorse['enable'] = false
prometheus_monitoring['enable'] = false

# Enable only the Praefect service
gitaly['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'] = 'GITLAB_SERVER_URL'

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 (eg 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 (eg 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
```

Complete these steps 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

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 praefect as the Praefect storage name.

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

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

You will need to replace:

PRAEFECT_HOST with the IP address or hostname of the Praefect node
PRAEFECT_EXTERNAL_TOKEN with the real secret

git_data_dirs({
  "default" => {
    "path" => "/var/opt/gitlab/git-data"
  },
  "praefect" => {
    "gitaly_address" => "tcp://PRAEFECT_HOST:2305",
    "gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
  }
})

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'
```
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 URL on which current GitLab instance is serving:
```
external_url 'GITLAB_SERVER_URL'
```

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
      ]
    ]
  },
  {
    '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
```

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.
- Deselect the default storage location
- Select the praefect storage location
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!

Congratulations! You have configured a highly available Praefect cluster.

Failover

There are two ways to do a failover from one internal Gitaly node to another as the primary. Manually, or automatically.

As an example, in this config.toml we have one virtual storage named "default" with two internal Gitaly nodes behind it. One is deemed the "primary". This means that read and write traffic will go to internal_storage_0, and writes will get replicated to internal_storage_1:

socket_path = "/path/to/Praefect.socket"

# failover_enabled will enable automatic failover
failover_enabled = false

[logging]
format = "json"
level = "info"

[[virtual_storage]]
name = "default"

[[virtual_storage.node]]
  name = "internal_storage_0"
  address = "tcp://localhost:9999"
  primary = true
  token = "supersecret"

[[virtual_storage.node]]
  name = "internal_storage_1"
  address = "tcp://localhost:9998"
  token = "supersecret"

Manual failover

In order to failover from using one internal Gitaly node to using another, a manual failover step can be used. Unless failover_enabled is set to true in the config.toml, the only way to fail over from one primary to using another node as the primary is to do a manual failover.

Move primary = true from the current [[virtual_storage.node]] to another node in /etc/gitlab/gitlab.rb:

praefect['virtual_storages'] = {
  'praefect' => {
    'gitaly-1' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN',
      # no longer the primary
    },
    'gitaly-2' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN',
      # this is the new primary
      'primary' => true
    },
    'gitaly-3' => {
      'address' => 'tcp://GITALY_HOST:8075',
      'token'   => 'PRAEFECT_INTERNAL_TOKEN',
    }
  }
}

Save the file and reconfigure GitLab.

On a restart, Praefect will send write traffic to internal_storage_1. internal_storage_0 is the new secondary now, and replication jobs will be created to replicate repository data to internal_storage_0 from internal_storage_1

Automatic failover

When automatic failover is enabled, Praefect will do automatic detection of the health of internal Gitaly nodes. If the primary has a certain amount of health checks fail, it will decide to promote one of the secondaries to be primary, and demote the primary to be a secondary.

To enable automatic failover, edit /etc/gitlab/gitlab.rb:

# failover_enabled turns on automatic failover
praefect['failover_enabled'] = true
praefect['virtual_storages'] = {
  'praefect' => {
    '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 file and reconfigure GitLab.

Below is the picture when Praefect starts up with the config.toml above:

graph TD
  A[Praefect] -->|Mutator RPC| B(internal_storage_0)
  B --> |Replication|C[internal_storage_1]

Let's say suddenly internal_storage_0 goes down. Praefect will detect this and automatically switch over to internal_storage_1, and internal_storage_0 will serve as a secondary:

graph TD
  A[Praefect] -->|Mutator RPC| B(internal_storage_1)
  B --> |Replication|C[internal_storage_0]

NOTE: Note:: Currently this feature is supported for setups that only have 1 Praefect instance. Praefect instances running, for example behind a load balancer, failover_enabled should be disabled. The reason is The reason is because there is no coordination that currently happens across different Praefect instances, so there could be a situation where two Praefect instances think two different Gitaly nodes are the primary.

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 subcommand 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.

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.

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.

26 KiB Raw Blame History

Praefect: High Availability

Requirements for configuring Gitaly for High Availability

Setup Instructions

Preparation

Secrets

PostgreSQL

Praefect

Gitaly

GitLab

Failover

Manual failover

Automatic failover

Backend Node Recovery

Grafana

Migrating existing repositories to Praefect

Debugging Praefect

26 KiB

Raw Blame History