debian-mirror-gitlab/doc/administration/redis/replication_and_failover.md

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Redis replication and failover with Omnibus GitLab (PREMIUM ONLY)

NOTE: Note: This is the documentation for the Omnibus GitLab packages. For using your own non-bundled Redis, follow the relevant documentation.

NOTE: Note: In Redis lingo, primary is called master. In this document, primary is used instead of master, except the settings where master is required.

Using Redis in scalable environment is possible using a Primary x Replica topology with a Redis Sentinel service to watch and automatically start the failover procedure.

Redis requires authentication if used with Sentinel. See Redis Security documentation for more information. We recommend using a combination of a Redis password and tight firewall rules to secure your Redis service. You are highly encouraged to read the Redis Sentinel documentation before configuring Redis with GitLab to fully understand the topology and architecture.

Before diving into the details of setting up Redis and Redis Sentinel for a replicated topology, make sure you read this document once as a whole to better understand how the components are tied together.

You need at least 3 independent machines: physical, or VMs running into distinct physical machines. It is essential that all primary and replica Redis instances run in different machines. If you fail to provision the machines in that specific way, any issue with the shared environment can bring your entire setup down.

It is OK to run a Sentinel alongside of a primary or replica Redis instance. There should be no more than one Sentinel on the same machine though.

You also need to take into consideration the underlying network topology, making sure you have redundant connectivity between Redis / Sentinel and GitLab instances, otherwise the networks will become a single point of failure.

Running Redis in a scaled environment requires a few things:

• Multiple Redis instances
• Run Redis in a Primary x Replica topology
• Multiple Sentinel instances
• Application support and visibility to all Sentinel and Redis instances

Redis Sentinel can handle the most important tasks in an HA environment and that's to help keep servers online with minimal to no downtime. Redis Sentinel:

• Monitors Primary and Replicas instances to see if they are available
• Promotes a Replica to Primary when the Primary fails
• Demotes a Primary to Replica when the failed Primary comes back online (to prevent data-partitioning)
• Can be queried by the application to always connect to the current Primary server

When a Primary fails to respond, it's the application's responsibility (in our case GitLab) to handle timeout and reconnect (querying a Sentinel for a new Primary).

To get a better understanding on how to correctly set up Sentinel, please read the Redis Sentinel documentation first, as failing to configure it correctly can lead to data loss or can bring your whole cluster down, invalidating the failover effort.

Recommended setup

For a minimal setup, you will install the Omnibus GitLab package in 3 independent machines, both with Redis and Sentinel:

• Redis Primary + Sentinel
• Redis Replica + Sentinel
• Redis Replica + Sentinel

If you are not sure or don't understand why and where the amount of nodes come from, read Redis setup overview and Sentinel setup overview.

For a recommended setup that can resist more failures, you will install the Omnibus GitLab package in 5 independent machines, both with Redis and Sentinel:

• Redis Primary + Sentinel
• Redis Replica + Sentinel
• Redis Replica + Sentinel
• Redis Replica + Sentinel
• Redis Replica + Sentinel

Redis setup overview

You must have at least 3 Redis servers: 1 primary, 2 Replicas, and they need to each be on independent machines (see explanation above).

You can have additional Redis nodes, that will help survive a situation where more nodes goes down. Whenever there is only 2 nodes online, a failover will not be initiated.

As an example, if you have 6 Redis nodes, a maximum of 3 can be simultaneously down.

Please note that there are different requirements for Sentinel nodes. If you host them in the same Redis machines, you may need to take that restrictions into consideration when calculating the amount of nodes to be provisioned. See Sentinel setup overview documentation for more information.

All Redis nodes should be configured the same way and with similar server specs, as in a failover situation, any Replica can be promoted as the new Primary by the Sentinel servers.

The replication requires authentication, so you need to define a password to protect all Redis nodes and the Sentinels. They will all share the same password, and all instances must be able to talk to each other over the network.

Sentinel setup overview

Sentinels watch both other Sentinels and Redis nodes. Whenever a Sentinel detects that a Redis node is not responding, it will announce that to the other Sentinels. They have to reach the quorum, that is the minimum amount of Sentinels that agrees a node is down, in order to be able to start a failover.

Whenever the quorum is met, the majority of all known Sentinel nodes need to be available and reachable, so that they can elect the Sentinel leader who will take all the decisions to restore the service availability by:

• Promoting a new Primary
• Reconfiguring the other Replicas and make them point to the new Primary
• Announce the new Primary to every other Sentinel peer
• Reconfigure the old Primary and demote to Replica when it comes back online

You must have at least 3 Redis Sentinel servers, and they need to be each in an independent machine (that are believed to fail independently), ideally in different geographical areas.

You can configure them in the same machines where you've configured the other Redis servers, but understand that if a whole node goes down, you loose both a Sentinel and a Redis instance.

The number of sentinels should ideally always be an odd number, for the consensus algorithm to be effective in the case of a failure.

In a 3 nodes topology, you can only afford 1 Sentinel node going down. Whenever the majority of the Sentinels goes down, the network partition protection prevents destructive actions and a failover will not be started.

Here are some examples:

• With 5 or 6 sentinels, a maximum of 2 can go down for a failover begin.
• With 7 sentinels, a maximum of 3 nodes can go down.

The Leader election can sometimes fail the voting round when consensus is not achieved (see the odd number of nodes requirement above). In that case, a new attempt will be made after the amount of time defined in sentinel['failover_timeout'] (in milliseconds).

NOTE: Note: We will see where sentinel['failover_timeout'] is defined later.

The failover_timeout variable has a lot of different use cases. According to the official documentation:

• The time needed to re-start a failover after a previous failover was already tried against the same primary by a given Sentinel, is two times the failover timeout.

• The time needed for a replica replicating to a wrong primary according to a Sentinel current configuration, to be forced to replicate with the right primary, is exactly the failover timeout (counting since the moment a Sentinel detected the misconfiguration).

• The time needed to cancel a failover that is already in progress but did not produced any configuration change (REPLICAOF NO ONE yet not acknowledged by the promoted replica).

• The maximum time a failover in progress waits for all the replicas to be reconfigured as replicas of the new primary. However even after this time the replicas will be reconfigured by the Sentinels anyway, but not with the exact parallel-syncs progression as specified.

Configuring Redis

This is the section where we install and set up the new Redis instances.

It is assumed that you have installed GitLab and all its components from scratch. If you already have Redis installed and running, read how to switch from a single-machine installation.

NOTE: Note: Redis nodes (both primary and replica) will need the same password defined in redis['password']. At any time during a failover the Sentinels can reconfigure a node and change its status from primary to replica and vice versa.

Requirements

The requirements for a Redis setup are the following:

1. Provision the minimum required number of instances as specified in the recommended setup section.
2. We Do not recommend installing Redis or Redis Sentinel in the same machines your GitLab application is running on as this weakens your HA configuration. You can however opt in to install Redis and Sentinel in the same machine.
3. All Redis nodes must be able to talk to each other and accept incoming connections over Redis (6379) and Sentinel (26379) ports (unless you change the default ones).
4. The server that hosts the GitLab application must be able to access the Redis nodes.
5. Protect the nodes from access from external networks (Internet), using firewall.

Switching from an existing single-machine installation

If you already have a single-machine GitLab install running, you will need to replicate from this machine first, before de-activating the Redis instance inside it.

Your single-machine install will be the initial Primary, and the 3 others should be configured as Replica pointing to this machine.

After replication catches up, you will need to stop services in the single-machine install, to rotate the Primary to one of the new nodes.

Make the required changes in configuration and restart the new nodes again.

To disable Redis in the single install, edit /etc/gitlab/gitlab.rb:

redis['enable'] = false

If you fail to replicate first, you may loose data (unprocessed background jobs).

Step 1. Configuring the primary Redis instance

1. SSH into the Primary Redis server.

2. Download/install the Omnibus GitLab package you want using steps 1 and 2 from the GitLab downloads page.

   • Make sure you select the correct Omnibus package, with the same version and type (Community, Enterprise editions) of your current install.
   • Do not complete any other steps on the download page.

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

   # Specify server role as 'redis_master_role'
   roles ['redis_master_role']
   
   # IP address pointing to a local IP that the other machines can reach to.
   # You can also set bind to '0.0.0.0' which listen in all interfaces.
   # If you really need to bind to an external accessible IP, make
   # sure you add extra firewall rules to prevent unauthorized access.
   redis['bind'] = '10.0.0.1'
   
   # Define a port so Redis can listen for TCP requests which will allow other
   # machines to connect to it.
   redis['port'] = 6379
   
   # Set up password authentication for Redis (use the same password in all nodes).
   redis['password'] = 'redis-password-goes-here'
   

4. Only the primary GitLab application server should handle migrations. To prevent database migrations from running on upgrade, add the following configuration to your /etc/gitlab/gitlab.rb file:

   gitlab_rails['auto_migrate'] = false
   

5. Reconfigure Omnibus GitLab for the changes to take effect.

NOTE: Note: You can specify multiple roles like sentinel and Redis as: roles ['redis_sentinel_role', 'redis_master_role']. Read more about roles.

Step 2. Configuring the replica Redis instances

1. SSH into the replica Redis server.

2. Download/install the Omnibus GitLab package you want using steps 1 and 2 from the GitLab downloads page.

   • Make sure you select the correct Omnibus package, with the same version and type (Community, Enterprise editions) of your current install.
   • Do not complete any other steps on the download page.

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

   # Specify server role as 'redis_replica_role'
   roles ['redis_replica_role']
   
   # IP address pointing to a local IP that the other machines can reach to.
   # You can also set bind to '0.0.0.0' which listen in all interfaces.
   # If you really need to bind to an external accessible IP, make
   # sure you add extra firewall rules to prevent unauthorized access.
   redis['bind'] = '10.0.0.2'
   
   # Define a port so Redis can listen for TCP requests which will allow other
   # machines to connect to it.
   redis['port'] = 6379
   
   # The same password for Redis authentication you set up for the primary node.
   redis['password'] = 'redis-password-goes-here'
   
   # The IP of the primary Redis node.
   redis['master_ip'] = '10.0.0.1'
   
   # Port of primary Redis server, uncomment to change to non default. Defaults
   # to `6379`.
   #redis['master_port'] = 6379
   

4. To prevent reconfigure from running automatically on upgrade, run:

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

5. Reconfigure Omnibus GitLab for the changes to take effect.

6. Go through the steps again for all the other replica nodes.

NOTE: Note: You can specify multiple roles like sentinel and Redis as: roles ['redis_sentinel_role', 'redis_master_role']. Read more about roles.

These values don't have to be changed again in /etc/gitlab/gitlab.rb after a failover, as the nodes will be managed by the Sentinels, and even after a gitlab-ctl reconfigure, they will get their configuration restored by the same Sentinels.

Step 3. Configuring the Redis Sentinel instances

NOTE: Note: If you are using an external Redis Sentinel instance, be sure to exclude the requirepass parameter from the Sentinel configuration. This parameter will cause clients to report NOAUTH Authentication required.. Redis Sentinel 3.2.x does not support password authentication.

Now that the Redis servers are all set up, let's configure the Sentinel servers.

If you are not sure if your Redis servers are working and replicating correctly, please read the Troubleshooting Replication and fix it before proceeding with Sentinel setup.

You must have at least 3 Redis Sentinel servers, and they need to be each in an independent machine. You can configure them in the same machines where you've configured the other Redis servers.

With GitLab Enterprise Edition, you can use the Omnibus package to set up multiple machines with the Sentinel daemon.

---

1. SSH into the server that will host Redis Sentinel.

2. You can omit this step if the Sentinels will be hosted in the same node as the other Redis instances.

   Download/install the Omnibus GitLab Enterprise Edition package using steps 1 and 2 from the GitLab downloads page.

   • Make sure you select the correct Omnibus package, with the same version the GitLab application is running.
   • Do not complete any other steps on the download page.

3. Edit /etc/gitlab/gitlab.rb and add the contents (if you are installing the Sentinels in the same node as the other Redis instances, some values might be duplicate below):

   roles ['redis_sentinel_role']
   
   # Must be the same in every sentinel node
   redis['master_name'] = 'gitlab-redis'
   
   # The same password for Redis authentication you set up for the primary node.
   redis['master_password'] = 'redis-password-goes-here'
   
   # The IP of the primary Redis node.
   redis['master_ip'] = '10.0.0.1'
   
   # Define a port so Redis can listen for TCP requests which will allow other
   # machines to connect to it.
   redis['port'] = 6379
   
   # Port of primary Redis server, uncomment to change to non default. Defaults
   # to `6379`.
   #redis['master_port'] = 6379
   
   ## Configure Sentinel
   sentinel['bind'] = '10.0.0.1'
   
   # Port that Sentinel listens on, uncomment to change to non default. Defaults
   # to `26379`.
   # sentinel['port'] = 26379
   
   ## Quorum must reflect the amount of voting sentinels it take to start a failover.
   ## Value must NOT be greater then the amount of sentinels.
   ##
   ## The quorum can be used to tune Sentinel in two ways:
   ## 1. If a the quorum is set to a value smaller than the majority of Sentinels
   ##    we deploy, we are basically making Sentinel more sensible to primary failures,
   ##    triggering a failover as soon as even just a minority of Sentinels is no longer
   ##    able to talk with the primary.
   ## 1. If a quorum is set to a value greater than the majority of Sentinels, we are
   ##    making Sentinel able to failover only when there are a very large number (larger
   ##    than majority) of well connected Sentinels which agree about the primary being down.s
   sentinel['quorum'] = 2
   
   ## Consider unresponsive server down after x amount of ms.
   # sentinel['down_after_milliseconds'] = 10000
   
   ## Specifies the failover timeout in milliseconds. It is used in many ways:
   ##
   ## - The time needed to re-start a failover after a previous failover was
   ##   already tried against the same primary by a given Sentinel, is two
   ##   times the failover timeout.
   ##
   ## - The time needed for a replica replicating to a wrong primary according
   ##   to a Sentinel current configuration, to be forced to replicate
   ##   with the right primary, is exactly the failover timeout (counting since
   ##   the moment a Sentinel detected the misconfiguration).
   ##
   ## - The time needed to cancel a failover that is already in progress but
   ##   did not produced any configuration change (REPLICAOF NO ONE yet not
   ##   acknowledged by the promoted replica).
   ##
   ## - The maximum time a failover in progress waits for all the replica to be
   ##   reconfigured as replicas of the new primary. However even after this time
   ##   the replicas will be reconfigured by the Sentinels anyway, but not with
   ##   the exact parallel-syncs progression as specified.
   # sentinel['failover_timeout'] = 60000
   

4. To prevent database migrations from running on upgrade, run:

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

   Only the primary GitLab application server should handle migrations.

5. Reconfigure Omnibus GitLab for the changes to take effect.

6. Go through the steps again for all the other Sentinel nodes.

Step 4. Configuring the GitLab application

The final part is to inform the main GitLab application server of the Redis Sentinels servers and authentication credentials.

You can enable or disable Sentinel support at any time in new or existing installations. From the GitLab application perspective, all it requires is the correct credentials for the Sentinel nodes.

While it doesn't require a list of all Sentinel nodes, in case of a failure, it needs to access at least one of the listed.

NOTE: Note: The following steps should be performed in the GitLab application server which ideally should not have Redis or Sentinels on it for a HA setup.

1. SSH into the server where the GitLab application is installed.

2. Edit /etc/gitlab/gitlab.rb and add/change the following lines:

   ## Must be the same in every sentinel node
   redis['master_name'] = 'gitlab-redis'
   
   ## The same password for Redis authentication you set up for the primary node.
   redis['master_password'] = 'redis-password-goes-here'
   
   ## A list of sentinels with `host` and `port`
   gitlab_rails['redis_sentinels'] = [
     {'host' => '10.0.0.1', 'port' => 26379},
     {'host' => '10.0.0.2', 'port' => 26379},
     {'host' => '10.0.0.3', 'port' => 26379}
   ]
   

3. Reconfigure Omnibus GitLab for the changes to take effect.

Step 5. Enable Monitoring

Introduced in GitLab 12.0.

If you enable Monitoring, it must be enabled on all Redis servers.

1. Make sure to collect CONSUL_SERVER_NODES, which are the IP addresses or DNS records of the Consul server nodes, for the next step. Note they are presented as Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z

2. Create/edit /etc/gitlab/gitlab.rb and add the following configuration:

   # Enable service discovery for Prometheus
   consul['enable'] = true
   consul['monitoring_service_discovery'] =  true
   
   # Replace placeholders
   # Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z
   # with the addresses of the Consul server nodes
   consul['configuration'] = {
      retry_join: %w(Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z),
   }
   
   # Set the network addresses that the exporters will listen on
   node_exporter['listen_address'] = '0.0.0.0:9100'
   redis_exporter['listen_address'] = '0.0.0.0:9121'
   

3. Run sudo gitlab-ctl reconfigure to compile the configuration.

Example of a minimal configuration with 1 primary, 2 replicas and 3 Sentinels

In this example we consider that all servers have an internal network interface with IPs in the 10.0.0.x range, and that they can connect to each other using these IPs.

In a real world usage, you would also set up firewall rules to prevent unauthorized access from other machines and block traffic from the outside (Internet).

We will use the same 3 nodes with Redis + Sentinel topology discussed in Redis setup overview and Sentinel setup overview documentation.

Here is a list and description of each machine and the assigned IP:

• 10.0.0.1: Redis primary + Sentinel 1
• 10.0.0.2: Redis Replica 1 + Sentinel 2
• 10.0.0.3: Redis Replica 2 + Sentinel 3
• 10.0.0.4: GitLab application

Please note that after the initial configuration, if a failover is initiated by the Sentinel nodes, the Redis nodes will be reconfigured and the Primary will change permanently (including in redis.conf) from one node to the other, until a new failover is initiated again.

The same thing will happen with sentinel.conf that will be overridden after the initial execution, after any new sentinel node starts watching the Primary, or a failover promotes a different Primary node.

Example configuration for Redis primary and Sentinel 1

In /etc/gitlab/gitlab.rb:

roles ['redis_sentinel_role', 'redis_master_role']
redis['bind'] = '10.0.0.1'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
redis['master_password'] = 'redis-password-goes-here' # the same value defined in redis['password'] in the primary instance
redis['master_ip'] = '10.0.0.1' # ip of the initial primary redis instance
#redis['master_port'] = 6379 # port of the initial primary redis instance, uncomment to change to non default
sentinel['bind'] = '10.0.0.1'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000

Reconfigure Omnibus GitLab for the changes to take effect.

Example configuration for Redis replica 1 and Sentinel 2

In /etc/gitlab/gitlab.rb:

roles ['redis_sentinel_role', 'redis_replica_role']
redis['bind'] = '10.0.0.2'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'
redis['master_ip'] = '10.0.0.1' # IP of primary Redis server
#redis['master_port'] = 6379 # Port of primary Redis server, uncomment to change to non default
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
sentinel['bind'] = '10.0.0.2'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000

Reconfigure Omnibus GitLab for the changes to take effect.

Example configuration for Redis replica 2 and Sentinel 3

In /etc/gitlab/gitlab.rb:

roles ['redis_sentinel_role', 'redis_replica_role']
redis['bind'] = '10.0.0.3'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'
redis['master_ip'] = '10.0.0.1' # IP of primary Redis server
#redis['master_port'] = 6379 # Port of primary Redis server, uncomment to change to non default
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
sentinel['bind'] = '10.0.0.3'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000

Reconfigure Omnibus GitLab for the changes to take effect.

Example configuration for the GitLab application

In /etc/gitlab/gitlab.rb:

redis['master_name'] = 'gitlab-redis'
redis['master_password'] = 'redis-password-goes-here'
gitlab_rails['redis_sentinels'] = [
  {'host' => '10.0.0.1', 'port' => 26379},
  {'host' => '10.0.0.2', 'port' => 26379},
  {'host' => '10.0.0.3', 'port' => 26379}
]

Reconfigure Omnibus GitLab for the changes to take effect.

Advanced configuration

Omnibus GitLab configures some things behind the curtains to make the sysadmins' lives easier. If you want to know what happens underneath keep reading.

Running multiple Redis clusters

GitLab supports running separate Redis clusters for different persistent classes: cache, queues, and shared_state. To make this work with Sentinel:

1. Set the appropriate variable in /etc/gitlab/gitlab.rb for each instance you are using:

   gitlab_rails['redis_cache_instance'] = REDIS_CACHE_URL
   gitlab_rails['redis_queues_instance'] = REDIS_QUEUES_URL
   gitlab_rails['redis_shared_state_instance'] = REDIS_SHARED_STATE_URL
   

   Note: Redis URLs should be in the format: redis://:PASSWORD@SENTINEL_PRIMARY_NAME

   1. PASSWORD is the plaintext password for the Redis instance
   2. SENTINEL_PRIMARY_NAME is the Sentinel primary name (e.g. gitlab-redis-cache)

2. Include an array of hashes with host/port combinations, such as the following:

   gitlab_rails['redis_cache_sentinels'] = [
     { host: REDIS_CACHE_SENTINEL_HOST, port: PORT1 },
     { host: REDIS_CACHE_SENTINEL_HOST2, port: PORT2 }
   ]
   gitlab_rails['redis_queues_sentinels'] = [
     { host: REDIS_QUEUES_SENTINEL_HOST, port: PORT1 },
     { host: REDIS_QUEUES_SENTINEL_HOST2, port: PORT2 }
   ]
   gitlab_rails['redis_shared_state_sentinels'] = [
     { host: SHARED_STATE_SENTINEL_HOST, port: PORT1 },
     { host: SHARED_STATE_SENTINEL_HOST2, port: PORT2 }
   ]
   

3. Note that for each persistence class, GitLab will default to using the configuration specified in gitlab_rails['redis_sentinels'] unless overridden by the settings above.

4. Be sure to include BOTH configuration options for each persistent classes. For example, if you choose to configure a cache instance, you must specify both gitlab_rails['redis_cache_instance'] and gitlab_rails['redis_cache_sentinels'] for GitLab to generate the proper configuration files.

5. Run gitlab-ctl reconfigure

Control running services

In the previous example, we've used redis_sentinel_role and redis_master_role which simplifies the amount of configuration changes.

If you want more control, here is what each one sets for you automatically when enabled:

## Redis Sentinel Role
redis_sentinel_role['enable'] = true

# When Sentinel Role is enabled, the following services are also enabled
sentinel['enable'] = true

# The following services are disabled
redis['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false

-------

## Redis primary/replica Role
redis_master_role['enable'] = true # enable only one of them
redis_replica_role['enable'] = true # enable only one of them

# When Redis primary or Replica role are enabled, the following services are
# enabled/disabled. Note that if Redis and Sentinel roles are combined, both
# services will be enabled.

# The following services are disabled
sentinel['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false

# For Redis Replica role, also change this setting from default 'true' to 'false':
redis['master'] = false

You can find the relevant attributes defined in gitlab_rails.rb.

Troubleshooting

See the Redis troubleshooting guide.

Further reading

Read more:

1. Reference architectures
2. Configure the database
3. Configure NFS
4. Configure the GitLab application servers
5. Configure the load balancers