Geo database replication (PREMIUM ONLY)

NOTE: Note: If your GitLab installation uses external (not managed by Omnibus) PostgreSQL instances, the Omnibus roles will not be able to perform all necessary configuration steps. In this case, follow the Geo with external PostgreSQL instances document instead.

NOTE: Note: The stages of the setup process must be completed in the documented order. Before attempting the steps in this stage, complete all prior stages.

This document describes the minimal steps you have to take in order to replicate your primary GitLab database to a secondary node's database. You may have to change some values according to your database setup, how big it is, etc.

You are encouraged to first read through all the steps before executing them in your testing/production environment.

PostgreSQL replication

The GitLab primary node where the write operations happen will connect to the primary database server, and secondary nodes will connect to their own database servers (which are also read-only).

We recommend using PostgreSQL replication slots to ensure that the primary node retains all the data necessary for the secondary nodes to recover. See below for more details.

The following guide assumes that:

You are using Omnibus and therefore you are using PostgreSQL 11 or later which includes the pg_basebackup tool and improved Foreign Data Wrapper support.
You have a primary node already set up (the GitLab server you are replicating from), running Omnibus' PostgreSQL (or equivalent version), and you have a new secondary server set up with the same versions of the OS, PostgreSQL, and GitLab on all nodes.

CAUTION: Warning: Geo works with streaming replication. Logical replication is not supported at this time. There is an issue where support is being discussed.

Step 1. Configure the primary server

SSH into your GitLab primary server and login as root:
```
sudo -i
```

Edit /etc/gitlab/gitlab.rb and add a unique name for your node:

# The unique identifier for the Geo node.
gitlab_rails['geo_node_name'] = '<node_name_here>'

Reconfigure the primary node for the change to take effect:
```
gitlab-ctl reconfigure
```
Execute the command below to define the node as primary node:
```
gitlab-ctl set-geo-primary-node
```
This command will use your defined external_url in /etc/gitlab/gitlab.rb.

GitLab 10.4 and up only: Do the following to make sure the gitlab database user has a password defined:

Generate a MD5 hash of the desired password:

gitlab-ctl pg-password-md5 gitlab
# Enter password: <your_password_here>
# Confirm password: <your_password_here>
# fca0b89a972d69f00eb3ec98a5838484

Edit /etc/gitlab/gitlab.rb:

# Fill with the hash generated by `gitlab-ctl pg-password-md5 gitlab`
postgresql['sql_user_password'] = '<md5_hash_of_your_password>'

# Every node that runs Puma or Sidekiq needs to have the database
# password specified as below. If you have a high-availability setup, this
# must be present in all application nodes.
gitlab_rails['db_password'] = '<your_password_here>'

Omnibus GitLab already has a replication user called gitlab_replicator. You must set the password for this user manually. You will be prompted to enter a password:
```
gitlab-ctl set-replication-password
```
This command will also read the postgresql['sql_replication_user'] Omnibus setting in case you have changed gitlab_replicator username to something else.

If you are using an external database not managed by Omnibus GitLab, you need to create the replicator user and define a password to it manually:
```
--- Create a new user 'replicator'
CREATE USER gitlab_replicator;

--- Set/change a password and grants replication privilege
ALTER USER gitlab_replicator WITH REPLICATION ENCRYPTED PASSWORD '<replication_password>';
```
Configure PostgreSQL to listen on network interfaces:

For security reasons, PostgreSQL does not listen on any network interfaces by default. However, Geo requires the secondary node to be able to connect to the primary node's database. For this reason, we need the address of each node.

NOTE: Note: For external PostgreSQL instances, see additional instructions.

If you are using a cloud provider, you can lookup the addresses for each Geo node through your cloud provider's management console.

To lookup the address of a Geo node, SSH in to the Geo node and execute:
```
##
## Private address
##
ip route get 255.255.255.255 | awk '{print "Private address:", $NF; exit}'

##
## Public address
##
echo "External address: $(curl --silent ipinfo.io/ip)"
```
In most cases, the following addresses will be used to configure GitLab Geo:

Configuration Address

postgresql['listen_address'] Primary node's public or VPC private address.

postgresql['md5_auth_cidr_addresses'] Secondary node's public or VPC private addresses.

If you are using Google Cloud Platform, SoftLayer, or any other vendor that provides a virtual private cloud (VPC) you can use the primary and secondary nodes private addresses (corresponds to "internal address" for Google Cloud Platform) for postgresql['md5_auth_cidr_addresses'] and postgresql['listen_address'].

The listen_address option opens PostgreSQL up to network connections with the interface corresponding to the given address. See the PostgreSQL documentation for more details.

Depending on your network configuration, the suggested addresses may not be correct. If your primary node and secondary nodes connect over a local area network, or a virtual network connecting availability zones like Amazon's VPC or Google's VPC you should use the secondary node's private address for postgresql['md5_auth_cidr_addresses'].

Edit /etc/gitlab/gitlab.rb and add the following, replacing the IP addresses with addresses appropriate to your network configuration:
```
##
## Geo Primary role
## - configure dependent flags automatically to enable Geo
##
roles ['geo_primary_role']

##
## Primary address
## - replace '<primary_node_ip>' with the public or VPC address of your Geo primary node
##
postgresql['listen_address'] = '<primary_node_ip>'

##
# Allow PostgreSQL client authentication from the primary and secondary IPs. These IPs may be
# public or VPC addresses in CIDR format, for example ['198.51.100.1/32', '198.51.100.2/32']
##
postgresql['md5_auth_cidr_addresses'] = ['<primary_node_ip>/32', '<secondary_node_ip>/32']

##
## Replication settings
## - set this to be the number of Geo secondary nodes you have
##
postgresql['max_replication_slots'] = 1
# postgresql['max_wal_senders'] = 10
# postgresql['wal_keep_segments'] = 10

##
## Disable automatic database migrations temporarily
## (until PostgreSQL is restarted and listening on the private address).
##
gitlab_rails['auto_migrate'] = false
```
Optional: If you want to add another secondary node, the relevant setting would look like:
```
postgresql['md5_auth_cidr_addresses'] = ['<primary_node_ip>/32', '<secondary_node_ip>/32', '<another_secondary_node_ip>/32']
```
You may also want to edit the wal_keep_segments and max_wal_senders to match your database replication requirements. Consult the PostgreSQL - Replication documentation for more information.
Save the file and reconfigure GitLab for the database listen changes and the replication slot changes to be applied:
```
gitlab-ctl reconfigure
```
Restart PostgreSQL for its changes to take effect:
```
gitlab-ctl restart postgresql
```
Re-enable migrations now that PostgreSQL is restarted and listening on the private address.

Edit /etc/gitlab/gitlab.rb and change the configuration to true:
```
gitlab_rails['auto_migrate'] = true
```
Save the file and reconfigure GitLab:
```
gitlab-ctl reconfigure
```
Now that the PostgreSQL server is set up to accept remote connections, run netstat -plnt | grep 5432 to make sure that PostgreSQL is listening on port 5432 to the primary server's private address.
A certificate was automatically generated when GitLab was reconfigured. This will be used automatically to protect your PostgreSQL traffic from eavesdroppers, but to protect against active ("man-in-the-middle") attackers, the secondary node needs a copy of the certificate. Make a copy of the PostgreSQL server.crt file on the primary node by running this command:
```
cat ~gitlab-psql/data/server.crt
```
Copy the output into a clipboard or into a local file. You will need it when setting up the secondary node! The certificate is not sensitive data.

Configuration	Address
`postgresql['listen_address']`	Primary node's public or VPC private address.
`postgresql['md5_auth_cidr_addresses']`	Secondary node's public or VPC private addresses.

Step 2. Configure the secondary server

SSH into your GitLab secondary server and login as root:
```
sudo -i
```
Stop application server and Sidekiq
```
gitlab-ctl stop puma
gitlab-ctl stop sidekiq
```
NOTE: Note: This step is important so we don't try to execute anything before the node is fully configured.
Check TCP connectivity to the primary node's PostgreSQL server:
```
gitlab-rake gitlab:tcp_check[<primary_node_ip>,5432]
```
NOTE: Note: If this step fails, you may be using the wrong IP address, or a firewall may be preventing access to the server. Check the IP address, paying close attention to the difference between public and private addresses and ensure that, if a firewall is present, the secondary node is permitted to connect to the primary node on port 5432.
Create a file server.crt in the secondary server, with the content you got on the last step of the primary node's setup:
```
editor server.crt
```
Set up PostgreSQL TLS verification on the secondary node:

Install the server.crt file:
```
install \
   -D \
   -o gitlab-psql \
   -g gitlab-psql \
   -m 0400 \
   -T server.crt ~gitlab-psql/.postgresql/root.crt
```
PostgreSQL will now only recognize that exact certificate when verifying TLS connections. The certificate can only be replicated by someone with access to the private key, which is only present on the primary node.
Test that the gitlab-psql user can connect to the primary node's database (the default Omnibus database name is gitlabhq_production):
```
sudo \
   -u gitlab-psql /opt/gitlab/embedded/bin/psql \
   --list \
   -U gitlab_replicator \
   -d "dbname=gitlabhq_production sslmode=verify-ca" \
   -W \
   -h <primary_node_ip>
```
When prompted enter the password you set in the first step for the gitlab_replicator user. If all worked correctly, you should see the list of primary node's databases.

A failure to connect here indicates that the TLS configuration is incorrect. Ensure that the contents of ~gitlab-psql/data/server.crt on the primary node match the contents of ~gitlab-psql/.postgresql/root.crt on the secondary node.

Configure PostgreSQL to enable FDW support:

This step is similar to how we configured the primary instance. We need to enable this, to enable FDW support, even if using a single node.

Edit /etc/gitlab/gitlab.rb and add the following, replacing the IP addresses with addresses appropriate to your network configuration:

##
## Geo Secondary role
## - configure dependent flags automatically to enable Geo
##
roles ['geo_secondary_role']

##
## Secondary address
## - replace '<secondary_node_ip>' with the public or VPC address of your Geo secondary node
##
postgresql['listen_address'] = '<secondary_node_ip>'
postgresql['md5_auth_cidr_addresses'] = ['<secondary_node_ip>/32']

##
## Database credentials password (defined previously in primary node)
## - replicate same values here as defined in primary node
##
postgresql['sql_user_password'] = '<md5_hash_of_your_password>'
gitlab_rails['db_password'] = '<your_password_here>'

##
## Enable FDW support for the Geo Tracking Database (improves performance)
##
geo_secondary['db_fdw'] = true

For external PostgreSQL instances, see additional instructions. If you bring a former primary node back online to serve as a secondary node, then you also need to remove roles ['geo_primary_role'] or geo_primary_role['enable'] = true.

Reconfigure GitLab for the changes to take effect:
```
gitlab-ctl reconfigure
```
Restart PostgreSQL for the IP change to take effect and reconfigure again:
```
gitlab-ctl restart postgresql
gitlab-ctl reconfigure
```
This last reconfigure will provision the FDW configuration and enable it.

Step 3. Initiate the replication process

Below we provide a script that connects the database on the secondary node to the database on the primary node, replicates the database, and creates the needed files for streaming replication.

The directories used are the defaults that are set up in Omnibus. If you have changed any defaults, configure it as you see fit replacing the directories and paths.

CAUTION: Warning: Make sure to run this on the secondary server as it removes all PostgreSQL's data before running pg_basebackup.

SSH into your GitLab secondary server and login as root:
```
sudo -i
```
Choose a database-friendly name to use for your secondary node to use as the replication slot name. For example, if your domain is secondary.geo.example.com, you may use secondary_example as the slot name as shown in the commands below.
Execute the command below to start a backup/restore and begin the replication

CAUTION: Warning: Each Geo secondary node must have its own unique replication slot name. Using the same slot name between two secondaries will break PostgreSQL replication.
```
gitlab-ctl replicate-geo-database \
   --slot-name=<secondary_node_name> \
   --host=<primary_node_ip>
```
NOTE: Note: Replication slot names must only contain lowercase letters, numbers, and the underscore character.

When prompted, enter the plaintext password you set up for the gitlab_replicator user in the first step.

This command also takes a number of additional options. You can use --help to list them all, but here are a couple of tips:
- If PostgreSQL is listening on a non-standard port, add --port= as well.
- If your database is too large to be transferred in 30 minutes, you will need to increase the timeout, e.g., --backup-timeout=3600 if you expect the initial replication to take under an hour.
- Pass --sslmode=disable to skip PostgreSQL TLS authentication altogether (e.g., you know the network path is secure, or you are using a site-to-site VPN). This is not safe over the public Internet!
- You can read more details about each sslmode in the PostgreSQL documentation; the instructions above are carefully written to ensure protection against both passive eavesdroppers and active "man-in-the-middle" attackers.
- Change the --slot-name to the name of the replication slot to be used on the primary database. The script will attempt to create the replication slot automatically if it does not exist.
- If you're repurposing an old server into a Geo secondary node, you'll need to add --force to the command line.
- When not in a production machine you can disable backup step if you really sure this is what you want by adding --skip-backup

The replication process is now complete.

PgBouncer support (optional)

PgBouncer may be used with GitLab Geo to pool PostgreSQL connections. We recommend using PgBouncer if you use GitLab in a high-availability configuration with a cluster of nodes supporting a Geo primary node and another cluster of nodes supporting a Geo secondary node. For more information, see High Availability with Omnibus GitLab.

For a Geo secondary node to work properly with PgBouncer in front of the database, it will need a separate read-only user to make PostgreSQL FDW queries work:

On the primary Geo database, enter the PostgreSQL on the console as an admin user. If you are using an Omnibus-managed database, log onto the primary node that is running the PostgreSQL database (the default Omnibus database name is gitlabhq_production):
```
 sudo \
    -u gitlab-psql /opt/gitlab/embedded/bin/psql \
    -h /var/opt/gitlab/postgresql gitlabhq_production
```

Then create the read-only user:

-- NOTE: Use the password defined earlier
CREATE USER gitlab_geo_fdw WITH password 'mypassword';
GRANT CONNECT ON DATABASE gitlabhq_production to gitlab_geo_fdw;
GRANT USAGE ON SCHEMA public TO gitlab_geo_fdw;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO gitlab_geo_fdw;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO gitlab_geo_fdw;

-- Tables created by "gitlab" should be made read-only for "gitlab_geo_fdw"
-- automatically.
ALTER DEFAULT PRIVILEGES FOR USER gitlab IN SCHEMA public GRANT SELECT ON TABLES TO gitlab_geo_fdw;
ALTER DEFAULT PRIVILEGES FOR USER gitlab IN SCHEMA public GRANT SELECT ON SEQUENCES TO gitlab_geo_fdw;

On the secondary nodes, change /etc/gitlab/gitlab.rb:

geo_postgresql['fdw_external_user'] = 'gitlab_geo_fdw'

Save the file and reconfigure GitLab for the changes to be applied:
```
gitlab-ctl reconfigure
```

Troubleshooting

Read the troubleshooting document.