GitLab Geo database replication

Note: This is the documentation for the Omnibus GitLab packages. For installations from source, follow the database replication for installations from source guide.

Note: 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 GitLab database into another server. 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 primary database server, and the secondary ones which are read-only will connect to secondary database servers (which are read-only too).

Note: In many databases documentation you will see "primary" being referenced as "master" and "secondary" as either "slave" or "standby" server (read-only).

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

Prerequisites

The following guide assumes that:

You are using PostgreSQL 9.6 or later which includes the pg_basebackup tool. If you are using Omnibus it includes the required PostgreSQL version for Geo.
You have a primary server 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 on the same OS and PostgreSQL version. Also make sure the GitLab version is the same on all nodes.
The IP of the primary server for our examples will be 1.2.3.4, whereas the secondary's IP will be 5.6.7.8. Note that the primary and secondary servers must be able to communicate over these addresses. These IP addresses can either be public or private.

If your GitLab installation is using external PostgreSQL, the Omnibus roles will not be able to perform all necessary configuration steps. Refer to External PostreSQL for additional instructions.

Step 1. Configure the primary server

SSH into your GitLab primary server and login as root:
```
sudo -i
```
Execute the command below to define the node as primary Geo node:
```
gitlab-ctl set-geo-primary-node
```
This command will use your defined external_url in /etc/gitlab/gitlab.rb.
Omnibus GitLab already has a replication user called gitlab_replicator. You must set its password manually. You will be prompted to enter a password:
```
gitlab-ctl set-replication-password
```
This command will also read postgresql['sql_replication_user'] Omnibus setting in case you have changed gitlab_replicator username to something else.

Configure PostgreSQL to listen on network interfaces

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

If you are using a cloud provider, you can lookup the addresses for each Geo node through their management console. A table of terminology is provided below because terminology varies between vendors.

GitLab Terminology	Amazon Web Services	Google Cloud Platform
Private address	Private address	Internal address
Public address	Public address	External address

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 ipinfo.io/ip)"

In most cases, the following addresses will be used to configure GitLab Geo:

Configuration	Address
`postgresql['listen_address']`	Primary's private address
`postgresql['trust_auth_cidr_addresses']`	Primary's private address
`postgresql['md5_auth_cidr_addresses']`	Secondary's public addresses

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 and secondary connect over a local area network, or a virtual network connecting availability zones like Amazon's VPC of Google's VPC you should use the secondary'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['enable'] = true

##
## Primary address
## - replace '1.2.3.4' with the primary private address
##
postgresql['listen_address'] = '1.2.3.4'
postgresql['trust_auth_cidr_addresses'] = ['127.0.0.1/32','1.2.3.4/32']

##
# Secondary addresses
# - replace '5.6.7.8' with the secondary public address
##
postgresql['md5_auth_cidr_addresses'] = ['5.6.7.8/32']

##
## 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

For external PostgreSQL instances, see additional instructions.

Optional: If you want to add another secondary, the relevant setting would look like:
```
postgresql['md5_auth_cidr_addresses'] = ['5.6.7.8/32','9.10.11.12/32']
```
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 to make sure that PostgreSQL is listening on port 5432 to the primary server's private address.
Make a copy of the PostgreSQL server.crt file 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 needs a copy of the certificate.

Run this command:

   cat ~gitlab-psql/data/server.crt

Copy the output into a file on your local computer called server.crt. You will need it when setting up the secondary! The certificate is not sensitive data.

Verify that clock synchronization is enabled.

Important: For Geo to work correctly, all nodes must have their clocks synchronized. It is not required for all nodes to be set to the same time zone, but when the respective times are converted to UTC time, the clocks must be synchronized to within 60 seconds of each other.

If you are using Ubuntu, verify NTP sync is enabled:
```
timedatectl status | grep 'NTP synchronized'
```
Refer to your Linux distribution documentation to setup clock synchronization. This can easily be done using any NTP-compatible daemon.

Step 2. Add the secondary GitLab node

To prevent the secondary geo node trying to act as the primary once the database is replicated, the secondary geo node must be configured on the primary before the database is replicated.

Visit the primary node's Admin Area ➔ Geo Nodes (/admin/geo_nodes) in your browser.
Add the secondary node by providing its full URL. Do NOT check the box 'This is a primary node'.
Optionally, choose which namespaces should be replicated by the secondary node. Leave blank to replicate all. Read more in selective replication.
Click the Add node button.

The new secondary geo node will have the status Unhealthy. This is expected because we have not yet configured the secondary server. This is the next step.

Step 3. Configure the secondary server

From your local machine, copy server.crt to the secondary:
```
scp server.crt secondary.geo.example.com:
```
SSH into your GitLab secondary server and login as root:
```
sudo -i
```
Set up PostgreSQL TLS verification on the secondary

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 remote connection to the primary server works (as the gitlab-psql user):
```
sudo -u gitlab-psql /opt/gitlab/embedded/bin/psql --list -U gitlab_replicator -d "dbname=gitlabhq_production sslmode=verify-ca" -W -h 1.2.3.4
```
When prompted enter the password you set in the first step for the gitlab_replicator user. If all worked correctly, you should see the database prompt.

A failure to connect here indicates that the TLS or networking configuration is incorrect. Ensure that you've used the correct certificates and IP addresses throughout. If you have a firewall, ensure that the secondary is permitted to access the primary on port 5432.
Edit /etc/gitlab/gitlab.rb and add the following:
```
geo_secondary_role['enable'] = true
```
For external PostgreSQL instances, see additional instructions.
[Reconfigure GitLab][] for the changes to take effect.
Verify that clock synchronization is enabled.

Important: For Geo to work correctly, all nodes must have their clocks synchronized. It is not required for all nodes to be set to the same time zone, but when the respective times are converted to UTC time, the clocks must be synchronized to within 60 seconds of each other.

If you are using Ubuntu, verify NTP sync is enabled:
```
timedatectl status | grep 'NTP synchronized'
```
Refer to your Linux distribution documentation to setup clock synchronization. This can easily be done using any NTP-compatible daemon.

Step 4. Initiate the replication process

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

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

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 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:
```
gitlab-ctl replicate-geo-database --slot-name=secondary_example --host=1.2.3.4
```
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.

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

New for 9.4: 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.

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 you're setting up replication on a brand-new secondary that has no data, you may want to pass --no-wait --skip-backup to speed up the process - but be certain that you're running it against the right GitLab installation first! It will cause data loss otherwise.

If you're repurposing an old server into a Geo secondary, you'll need to add --force to the command line.

The replication process is now over.

External PostgreSQL instances

For installations using external PostgreSQL instances, the geo_primary_role and geo_secondary_role includes configuration changes that must be applied manually.

The geo_primary_role makes configuration changes to pg_hba.conf and postgresql.conf on the primary:

##
## GitLab Geo Primary
## - pg_hba.conf
##
host    replication gitlab_replicator <trusted secondary IP>/32     md5

##
## Geo Primary Role
## - postgresql.conf
##
sql_replication_user = gitlab_replicator
wal_level = hot_standby
max_wal_senders = 10
wal_keep_segments = 50
max_replication_slots = 1 # number of secondary instances
hot_standby = on

Th geo_secondary_role makes configuration changes to postgresql.conf and enables the Geo Log Cursor (geo_logcursor) and secondary tracking database on the secondary. The PostgreSQL settings for this database it adds to the default settings:

##
## Geo Secondary Role
## - postgresql.conf
##
wal_level = hot_standby
max_wal_senders = 10
wal_keep_segments = 10
hot_standby = on

Geo secondary nodes use a tracking database to keep track of replication status and recover automatically from some replication issues. Follow the instructions for enabling tracking database on the secondary server.

MySQL replication

We don't support MySQL replication for GitLab Geo.

Troubleshooting

Read the troubleshooting document.