Geo database replication (source)

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

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 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.

The following guide assumes that:

You are using PostgreSQL 9.6 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 PostgreSQL 9.6 or later, and you have a new secondary server set up with the same versions of the OS, PostgreSQL, and GitLab 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.

Step 1. Configure the primary server

SSH into your GitLab primary server and login as root:
```
sudo -i
```
Add this node as the Geo primary by running:
```
bundle exec rake geo:set_primary_node
```

Create a replication user named gitlab_replicator:

--- 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 'replicationpasswordhere';

Make sure your the gitlab database user has a password defined

sudo -u postgres psql -d template1 -c "ALTER USER gitlab WITH ENCRYPTED PASSWORD 'mydatabasepassword';"

Edit the content of database.yml in production: and add the password like the exemple below:

#
# PRODUCTION
#
production:
  adapter: postgresql
  encoding: unicode
  database: gitlabhq_production
  pool: 10
  username: gitlab
  password: mydatabasepassword
  host: /var/opt/gitlab/geo-postgresql

Set up TLS support for the PostgreSQL primary server

Warning: Only skip this step if you know that PostgreSQL traffic between the primary and secondary will be secured through some other means, e.g., a known-safe physical network path or a site-to-site VPN that you have configured.

If you are replicating your database across the open Internet, it is essential that the connection is TLS-secured. Correctly configured, this provides protection against both passive eavesdroppers and active "man-in-the-middle" attackers.

To generate a self-signed certificate and key, run this command:
```
openssl req -nodes -batch -x509 -newkey rsa:4096 -keyout server.key -out server.crt -days 3650
```
This will create two files - server.key and server.crt - that you can use for authentication.

Copy them to the correct location for your PostgreSQL installation:
```
# Copying a self-signed certificate and key
install -o postgres -g postgres -m 0400 -T server.crt ~postgres/9.x/main/data/server.crt
install -o postgres -g postgres -m 0400 -T server.key ~postgres/9.x/main/data/server.key
```
Add this configuration to postgresql.conf, removing any existing configuration for ssl_cert_file or ssl_key_file:
```
ssl = on
ssl_cert_file='server.crt'
ssl_key_file='server.key'
```
Edit postgresql.conf to configure the primary server for streaming replication (for Debian/Ubuntu that would be /etc/postgresql/9.x/main/postgresql.conf):
```
listen_address = '1.2.3.4'
wal_level = hot_standby
max_wal_senders = 5
min_wal_size = 80MB
max_wal_size = 1GB
max_replicaton_slots = 1 # Number of Geo secondary nodes
wal_keep_segments = 10
hot_standby = on
```
Be sure to set max_replication_slots to the number of Geo secondary nodes that you may potentially have (at least 1).

For security reasons, PostgreSQL by default only listens on the local interface (e.g. 127.0.0.1). However, Geo needs to communicate between the primary and secondary nodes over a common network, such as a corporate LAN or the public Internet. For this reason, we need to configure PostgreSQL to listen on more interfaces.

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

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.
Set the access control on the primary to allow TCP connections using the server's public IP and set the connection from the secondary to require a password. Edit pg_hba.conf (for Debian/Ubuntu that would be /etc/postgresql/9.x/main/pg_hba.conf):
```
host    all             all                      1.2.3.4/32      md5
host    replication     gitlab_replicator        5.6.7.8/32      md5
```
Where 1.2.3.4 is the public IP address of the primary server, and 5.6.7.8 the public IP address of the secondary one. If you want to add another secondary, add one more row like the replication one and change the IP address:
```
host    all             all                      1.2.3.4/32      md5
host    replication     gitlab_replicator        5.6.7.8/32      md5
host    replication     gitlab_replicator        11.22.33.44/32  md5
```
Restart PostgreSQL for the changes to take effect.
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.

Create the replication slot on the primary:

$ sudo -u postgres psql -c "SELECT * FROM pg_create_physical_replication_slot('secondary_example');"
  slot_name         | xlog_position
  ------------------+---------------
  secondary_example |
  (1 row)

Now that the PostgreSQL server is set up to accept remote connections, run netstat -plnt to make sure that PostgreSQL is listening to the server's public IP.

Step 2. Configure the secondary server

Follow the first steps in "configure the secondary server", but note that since you are installing from source, the username and group listed as gitlab-psql in those steps should be replaced by postgres instead. After completing the "Test that the gitlab-psql user can connect to the primary's database" step, continue here:

Edit postgresql.conf to configure the secondary for streaming replication (for Debian/Ubuntu that would be /etc/postgresql/9.*/main/postgresql.conf):
```
wal_level = hot_standby
max_wal_senders = 5
checkpoint_segments = 10
wal_keep_segments = 10
hot_standby = on
```
Restart PostgreSQL for the changes to take effect.

Enable tracking database on the secondary server

Geo secondary nodes use a tracking database to keep track of replication status and recover automatically from some replication issues. Follow the steps below to create the tracking database.

On the secondary node, run the following command to create database_geo.yml with the information of your secondary PostgreSQL instance:
```
sudo cp /home/git/gitlab/config/database_geo.yml.postgresql /home/git/gitlab/config/database_geo.yml
```

Edit the content of database_geo.yml in production: as in the example below:

#
# PRODUCTION
#
production:
  adapter: postgresql
  encoding: unicode
  database: gitlabhq_geo_production
  pool: 10
  username: gitlab_geo
  # password:
  host: /var/opt/gitlab/geo-postgresql

Create the database gitlabhq_geo_production on the PostgreSQL instance of the secondary node.
Set up the Geo tracking database:
```
bundle exec rake geo:db:migrate
```

Configure the PostgreSQL FDW connection and credentials:

Save the script below in a file, ex. /tmp/geo_fdw.sh and modify the connection params to match your environment. Execute it to setup the FDW connection.

#!/bin/bash

# Secondary Database connection params:
DB_HOST="/var/opt/gitlab/postgresql" # change to the public IP or VPC private IP if its an external server
DB_NAME="gitlabhq_production"
DB_USER="gitlab"
DB_PORT="5432"

# Tracking Database connection params:
GEO_DB_HOST="/var/opt/gitlab/geo-postgresql" # change to the public IP or VPC private IP if its an external server
GEO_DB_NAME="gitlabhq_geo_production"
GEO_DB_USER="gitlab_geo"
GEO_DB_PORT="5432"

query_exec () {
  gitlab-psql -h $GEO_DB_HOST -d $GEO_DB_NAME -p $GEO_DB_PORT -c "${1}"
}

query_exec "CREATE EXTENSION postgres_fdw;"
query_exec "CREATE SERVER gitlab_secondary FOREIGN DATA WRAPPER postgres_fdw OPTIONS (host '${DB_HOST}', dbname '${DB_NAME}', port '${DB_PORT}');"
query_exec "CREATE USER MAPPING FOR ${GEO_DB_USER} SERVER gitlab_secondary OPTIONS (user '${DB_USER}');"
query_exec "CREATE SCHEMA gitlab_secondary;"
query_exec "GRANT USAGE ON FOREIGN SERVER gitlab_secondary TO ${GEO_DB_USER};"

And edit the content of database_geo.yml and to add fdw: true to the production: block.

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 for Debian/Ubuntu. If you have changed any defaults, 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
```

Save the snippet below in a file, let's say /tmp/replica.sh. Modify the embedded paths if necessary:

#!/bin/bash

PORT="5432"
USER="gitlab_replicator"
echo ---------------------------------------------------------------
echo WARNING: Make sure this script is run from the secondary server
echo ---------------------------------------------------------------
echo
echo Enter the IP or FQDN of the primary PostgreSQL server
read HOST
echo Enter the password for $USER@$HOST
read -s PASSWORD
echo Enter the required sslmode
read SSLMODE

echo Stopping PostgreSQL and all GitLab services
sudo service gitlab stop
sudo service postgresql stop

echo Backing up postgresql.conf
sudo -u postgres mv /var/opt/gitlab/postgresql/data/postgresql.conf /var/opt/gitlab/postgresql/

echo Cleaning up old cluster directory
sudo -u postgres rm -rf /var/opt/gitlab/postgresql/data

echo Starting base backup as the replicator user
echo Enter the password for $USER@$HOST
sudo -u postgres /opt/gitlab/embedded/bin/pg_basebackup -h $HOST -D /var/opt/gitlab/postgresql/data -U gitlab_replicator -v -x -P

echo Writing recovery.conf file
sudo -u postgres bash -c "cat > /var/opt/gitlab/postgresql/data/recovery.conf <<- _EOF1_
  standby_mode = 'on'
  primary_conninfo = 'host=$HOST port=$PORT user=$USER password=$PASSWORD sslmode=$SSLMODE'
_EOF1_
"

echo Restoring postgresql.conf
sudo -u postgres mv /var/opt/gitlab/postgresql/postgresql.conf /var/opt/gitlab/postgresql/data/

echo Starting PostgreSQL
sudo service postgresql start

Run it with:
```
bash /tmp/replica.sh
```
When prompted, enter the IP/FQDN of the primary, and the password you set up for the gitlab_replicator user in the first step.

You should use verify-ca for the sslmode. You can use disable if you are happy 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.

The replication process is now over.

MySQL replication

MySQL replication is not supported for Geo.

Troubleshooting

Read the troubleshooting document.