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# Praefect: High Availability
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NOTE: **Note:** Praefect is an experimental service, and data loss is likely.
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Praefect is an optional reverse-proxy for [Gitaly ](../index.md ) to manage a
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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.
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The first minimal version will support:
- Eventual consistency of the secondary replicas.
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- Automatic fail over from the primary to the secondary.
- Reporting of possible data loss if replication queue is non empty.
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Follow the [HA Gitaly epic ](https://gitlab.com/groups/gitlab-org/-/epics/1489 )
for updates and roadmap.
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## Requirements for configuring Gitaly for High Availability
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NOTE: **Note:** this reference architecture is not highly available because
Praefect is a single point of failure.
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The minimal [alpha ](https://about.gitlab.com/handbook/product/#alpha-beta-ga )
reference architecture additionally requires:
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- 1 Praefect node
- 1 PostgreSQL server (PostgreSQL 9.6 or newer)
- 3 Gitaly nodes (1 primary, 2 secondary)
![Alpha architecture diagram ](img/praefect_architecture_v12_9.png )
See the [design
document](https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/design_ha.md)
for implementation details.
## Setup Instructions
If you [installed ](https://about.gitlab.com/install/ ) GitLab using the Omnibus
package (highly recommended), follow the steps below:
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1. [Preparation ](#preparation )
1. [Configuring the Praefect database ](#postgresql )
1. [Configuring the Praefect proxy/router ](#praefect )
1. [Configuring each Gitaly node ](#gitaly ) (once for each Gitaly node)
1. [Updating the GitLab server configuration ](#gitlab )
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### Preparation
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Before beginning, you should already have a working GitLab instance. [Learn how
to install GitLab](https://about.gitlab.com/install/).
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Provision a PostgreSQL server (PostgreSQL 9.6 or newer). Configuration through
the GitLab Omnibus distribution is not yet supported. Follow this
[issue ](https://gitlab.com/gitlab-org/gitaly/issues/2476 ) for updates.
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Prepare all your new nodes by [installing
GitLab](https://about.gitlab.com/install/).
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- 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.
1. `POSTGRESQL_SERVER_ADDRESS` : the IP/host address of the PostgreSQL server
1. `PRAEFECT_SERVER_ADDRESS` : the IP/host address of the Praefect server
1. `GITALY_SERVER_ADDRESS` : the IP/host address of each Gitaly node
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#### Secrets
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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.
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.
1. `PRAEFECT_EXTERNAL_TOKEN` : repositories hosted on your Praefect cluster can
only be accessed by Gitaly clients that carry this token.
1. `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.
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1. `PRAEFECT_SQL_PASSWORD` : this password is used by Praefect to connect to
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PostgreSQL.
1. `GRAFANA_PASSWORD` : this password is used to access the `admin`
account in the Grafana dashboards.
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We will note in the instructions below where these secrets are required.
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### PostgreSQL
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NOTE: **Note:** don't reuse the GitLab application database for the Praefect
database.
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To complete this section you will need:
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- 1 Praefect node
- 1 PostgreSQL server (PostgreSQL 9.6 or newer)
- An SQL user with permissions to create databases
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During this section, we will configure the PostgreSQL server, from the Praefect
node, using `psql` which is installed by GitLab Omnibus.
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1. SSH into the **Praefect** node and login as root:
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```shell
sudo -i
```
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1. 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.
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```shell
/opt/gitlab/embedded/bin/psql -U postgres -d template1 -h POSTGRESQL_SERVER_ADDRESS
```
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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.
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```sql
CREATE ROLE praefect WITH LOGIN CREATEDB PASSWORD 'PRAEFECT_SQL_PASSWORD';
```
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1. Reconnect to the PostgreSQL server, this time as the `praefect` user:
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```shell
/opt/gitlab/embedded/bin/psql -U praefect -d template1 -h POSTGRESQL_SERVER_ADDRESS
```
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Create a new database `praefect_production` . By creating the database while
connected as the `praefect` user, we are confident they have access.
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```sql
CREATE DATABASE praefect_production WITH ENCODING=UTF8;
```
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The database used by Praefect is now configured.
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### Praefect
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To complete this section you will need:
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- [Configured PostgreSQL server ](#postgresql ), including:
- IP/host address (`POSTGRESQL_SERVER_ADDRESS`)
- password (`PRAEFECT_SQL_PASSWORD`)
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Praefect should be run on a dedicated node. Do not run Praefect on the
application server, or a Gitaly node.
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1. SSH into the **Praefect** node and login as root:
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```shell
sudo -i
```
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1. Disable all other services by editing `/etc/gitlab/gitlab.rb` :
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```ruby
# 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
```
1. Configure **Praefect** to listen on network interfaces by editing
`/etc/gitlab/gitlab.rb` :
```ruby
# 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'
```
1. 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 :
```ruby
praefect['auth_token'] = 'PRAEFECT_EXTERNAL_TOKEN'
```
1. 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.
```ruby
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:
```ruby
# 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:
```ruby
# praefect['database_sslmode'] = 'disable'
```
1. 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.
```ruby
# 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'
}
}
}
```
1. Save the changes to `/etc/gitlab/gitlab.rb` and [reconfigure Praefect ](../restart_gitlab.md#omnibus-gitlab-reconfigure ):
```shell
gitlab-ctl reconfigure
```
1. Verify that Praefect can reach PostgreSQL:
```shell
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 ](#praefect )
- 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 ](../index.md ),
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 ](#praefect ). 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 ](#praefect ). 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](index.md#3-gitaly-server-configuration).
1. SSH into the **Gitaly** node and login as root:
```shell
sudo -i
```
1. Disable all other services by editing `/etc/gitlab/gitlab.rb` :
```ruby
# 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
```
1. Configure **Gitaly** to listen on network interfaces by editing
`/etc/gitlab/gitlab.rb` :
```ruby
# 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'
```
1. 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.
```ruby
gitaly['auth_token'] = 'PRAEFECT_INTERNAL_TOKEN'
```
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1. 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 ](../index.md )
```ruby
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'
```
1. 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.
```ruby
# 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"
}
})
```
1. Save the changes to `/etc/gitlab/gitlab.rb` and [reconfigure Gitaly ](../restart_gitlab.md#omnibus-gitlab-reconfigure ):
```shell
gitlab-ctl reconfigure
```
1. To ensure that Gitaly [has updated its Prometheus listen address ](https://gitlab.com/gitlab-org/gitaly/-/issues/2521 ), [restart Gitaly ](../restart_gitlab.md#omnibus-gitlab-restart ):
```shell
gitlab-ctl restart gitaly
```
**Complete these steps for each Gitaly node!**
After all Gitaly nodes are configured, you can run the Praefect connection
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checker to verify Praefect can connect to all Gitaly servers in the Praefect
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config.
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1. SSH into the **Praefect** node and run the Praefect connection checker:
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```shell
sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml dial-nodes
```
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### GitLab
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To complete this section you will need:
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- [Configured Praefect node ](#praefect )
- [Configured Gitaly nodes ](#gitaly )
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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 ](#praefect ) section of this guide. This document uses
`praefect` as the Praefect storage name.
1. SSH into the **GitLab** node and login as root:
```shell
sudo -i
```
1. 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
```ruby
git_data_dirs({
"default" => {
"path" => "/var/opt/gitlab/git-data"
},
"praefect" => {
"gitaly_address" => "tcp://PRAEFECT_HOST:2305",
"gitaly_token" => 'PRAEFECT_EXTERNAL_TOKEN'
}
})
```
1. 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.
```ruby
gitlab_shell['secret_token'] = 'GITLAB_SHELL_SECRET_TOKEN'
```
1. 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:
```ruby
external_url 'GITLAB_SERVER_URL'
```
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1. Add Prometheus monitoring settings by editing `/etc/gitlab/gitlab.rb` .
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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
```ruby
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
]
]
}
]
grafana['disable_login_form'] = false
```
1. Save the changes to `/etc/gitlab/gitlab.rb` and [reconfigure GitLab ](../restart_gitlab.md#omnibus-gitlab-reconfigure ):
```shell
gitlab-ctl reconfigure
```
1. Verify that GitLab can reach Praefect:
```shell
gitlab-rake gitlab:gitaly:check
```
1. Set the Grafana admin password. This command will prompt you to enter a new password:
```shell
gitlab-ctl set-grafana-password
```
1. 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
1. 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!
1. Inspect metrics by browsing to `/-/grafana` on your GitLab server.
Log in with `admin` / `GRAFANA_PASSWORD` . Go to 'Explore' and query
`gitlab_build_info` to verify that you are getting metrics from all your
machines.
Congratulations! You have configured a highly available Praefect cluster.
## 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](../../api/projects.html#edit-project):
```shell
curl --request PUT \
--header "PRIVATE-TOKEN: < your_access_token > " \
--data "repository_storage=praefect" \
https://example.gitlab.com/api/v4/projects/123
```
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## Debugging Praefect
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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...)**
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- Praefect cannot reach one or more of its child Gitaly nodes. Try running
the Praefect connection checker to diagnose.