PostgreSQL replication and failover with Omnibus GitLab

This document will focus only on configuration supported with GitLab Premium, using the Omnibus GitLab package. If you are a Community Edition or Starter user, consider using a cloud hosted solution. This document will not cover installations from source.

If a setup with replication and failover is not what you were looking for, see the database configuration document for the Omnibus GitLab packages.

It’s recommended to read this document fully before attempting to configure PostgreSQL with replication and failover for GitLab.

Architecture

The Omnibus GitLab recommended configuration for a PostgreSQL cluster with replication and failover requires:

  • A minimum of three database nodes.
  • A minimum of three Consul server nodes.
  • A minimum of one pgbouncer service node, but it’s recommended to have one per database node.
    • An internal load balancer (TCP) is required when there is more than one pgbouncer service node.

PostgreSQL HA Architecture

You also need to take into consideration the underlying network topology, making sure you have redundant connectivity between all Database and GitLab instances to avoid the network becoming a single point of failure.

Note: As of GitLab 13.3, PostgreSQL 12 is shipped with Omnibus GitLab. Clustering for PostgreSQL 12 is only supported with Patroni. See the Patroni section for further details. The support for repmgr will not be extended beyond PostgreSQL 11.

Database node

Each database node runs three services:

PostgreSQL - The database itself.

repmgrd - Communicates with other repmgrd services in the cluster and handles failover when issues with the master server occurs. The failover procedure consists of:

  • Selecting a new master for the cluster.
  • Promoting the new node to master.
  • Instructing remaining servers to follow the new master node.
  • The old master node is automatically evicted from the cluster and should be rejoined manually once recovered.

Consul agent - Monitors the status of each node in the database cluster and tracks its health in a service definition on the Consul cluster.

Consul server node

The Consul server node runs the Consul server service.

PgBouncer node

Each PgBouncer node runs two services:

PgBouncer - The database connection pooler itself.

Consul agent - Watches the status of the PostgreSQL service definition on the Consul cluster. If that status changes, Consul runs a script which updates the PgBouncer configuration to point to the new PostgreSQL master node and reloads the PgBouncer service.

Connection flow

Each service in the package comes with a set of default ports. You may need to make specific firewall rules for the connections listed below:

Setting it up

Required information

Before proceeding with configuration, you will need to collect all the necessary information.

Network information

PostgreSQL does not listen on any network interface by default. It needs to know which IP address to listen on in order to be accessible to other services. Similarly, PostgreSQL access is controlled based on the network source.

This is why you will need:

  • IP address of each nodes network interface. This can be set to 0.0.0.0 to listen on all interfaces. It cannot be set to the loopback address 127.0.0.1.
  • Network Address. This can be in subnet (i.e. 192.168.0.0/255.255.255.0) or CIDR (i.e. 192.168.0.0/24) form.

Consul information

When using default setup, minimum configuration requires:

  • CONSUL_USERNAME. The default user for Omnibus GitLab is gitlab-consul
  • CONSUL_DATABASE_PASSWORD. Password for the database user.
  • CONSUL_PASSWORD_HASH. This is a hash generated out of Consul username/password pair. Can be generated with:

     sudo gitlab-ctl pg-password-md5 CONSUL_USERNAME
    
  • CONSUL_SERVER_NODES. The IP addresses or DNS records of the Consul server nodes.

Few notes on the service itself:

  • The service runs under a system account, by default gitlab-consul.
    • If you are using a different username, you will have to specify it. We will refer to it with CONSUL_USERNAME,
  • There will be a database user created with read only access to the repmgr database
  • Passwords will be stored in the following locations:
    • /etc/gitlab/gitlab.rb: hashed
    • /var/opt/gitlab/pgbouncer/pg_auth: hashed
    • /var/opt/gitlab/consul/.pgpass: plaintext

PostgreSQL information

When configuring PostgreSQL, we will set max_wal_senders to one more than the number of database nodes in the cluster. This is used to prevent replication from using up all of the available database connections.

In this document we are assuming 3 database nodes, which makes this configuration:

postgresql['max_wal_senders'] = 4

As previously mentioned, you’ll have to prepare the network subnets that will be allowed to authenticate with the database. You’ll also need to supply the IP addresses or DNS records of Consul server nodes.

We will need the following password information for the application’s database user:

  • POSTGRESQL_USERNAME. The default user for Omnibus GitLab is gitlab
  • POSTGRESQL_USER_PASSWORD. The password for the database user
  • POSTGRESQL_PASSWORD_HASH. This is a hash generated out of the username/password pair. Can be generated with:

    sudo gitlab-ctl pg-password-md5 POSTGRESQL_USERNAME
    

PgBouncer information

When using default setup, minimum configuration requires:

  • PGBOUNCER_USERNAME. The default user for Omnibus GitLab is pgbouncer
  • PGBOUNCER_PASSWORD. This is a password for PgBouncer service.
  • PGBOUNCER_PASSWORD_HASH. This is a hash generated out of PgBouncer username/password pair. Can be generated with:

    sudo gitlab-ctl pg-password-md5 PGBOUNCER_USERNAME
    
  • PGBOUNCER_NODE, is the IP address or a FQDN of the node running PgBouncer.

Few notes on the service itself:

  • The service runs as the same system account as the database
    • In the package, this is by default gitlab-psql
  • If you use a non-default user account for PgBouncer service (by default pgbouncer), you will have to specify this username. We will refer to this requirement with PGBOUNCER_USERNAME.
  • The service will have a regular database user account generated for it
    • This defaults to repmgr
  • Passwords will be stored in the following locations:
    • /etc/gitlab/gitlab.rb: hashed, and in plain text
    • /var/opt/gitlab/pgbouncer/pg_auth: hashed

Repmgr information

When using default setup, you will only have to prepare the network subnets that will be allowed to authenticate with the service.

Few notes on the service itself:

  • The service runs under the same system account as the database
    • In the package, this is by default gitlab-psql
  • The service will have a superuser database user account generated for it
    • This defaults to gitlab_repmgr

Installing Omnibus GitLab

First, make sure to download/install Omnibus GitLab on each node.

Make sure you install the necessary dependencies from step 1, add GitLab package repository from step 2. When installing the GitLab package, do not supply EXTERNAL_URL value.

Configuring the Database nodes

  1. Make sure to configure the Consul nodes.
  2. Make sure you collect CONSUL_SERVER_NODES, PGBOUNCER_PASSWORD_HASH, POSTGRESQL_PASSWORD_HASH, the number of db nodes, and the network address before executing the next step.

  3. On the master database node, edit /etc/gitlab/gitlab.rb replacing values noted in the # START user configuration section:

    # Disable all components except PostgreSQL and Repmgr and Consul
    roles ['postgres_role']
    
    # PostgreSQL configuration
    postgresql['listen_address'] = '0.0.0.0'
    postgresql['hot_standby'] = 'on'
    postgresql['wal_level'] = 'replica'
    postgresql['shared_preload_libraries'] = 'repmgr_funcs'
    
    # Disable automatic database migrations
    gitlab_rails['auto_migrate'] = false
    
    # Configure the Consul agent
    consul['services'] = %w(postgresql)
    
    # START user configuration
    # Please set the real values as explained in Required Information section
    #
    # Replace PGBOUNCER_PASSWORD_HASH with a generated md5 value
    postgresql['pgbouncer_user_password'] = 'PGBOUNCER_PASSWORD_HASH'
    # Replace POSTGRESQL_PASSWORD_HASH with a generated md5 value
    postgresql['sql_user_password'] = 'POSTGRESQL_PASSWORD_HASH'
    # Replace X with value of number of db nodes + 1
    postgresql['max_wal_senders'] = X
    postgresql['max_replication_slots'] = X
    
    # Replace XXX.XXX.XXX.XXX/YY with Network Address
    postgresql['trust_auth_cidr_addresses'] = %w(XXX.XXX.XXX.XXX/YY)
    repmgr['trust_auth_cidr_addresses'] = %w(127.0.0.1/32 XXX.XXX.XXX.XXX/YY)
    
    # Replace placeholders:
    #
    # Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z
    # with the addresses gathered for CONSUL_SERVER_NODES
    consul['configuration'] = {
      retry_join: %w(Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z)
    }
    #
    # END user configuration
    

    postgres_role was introduced with GitLab 10.3

  4. On secondary nodes, add all the configuration specified above for primary node to /etc/gitlab/gitlab.rb. In addition, append the following configuration to inform gitlab-ctl that they are standby nodes initially and it need not attempt to register them as primary node

    # Specify if a node should attempt to be master on initialization
    repmgr['master_on_initialization'] = false
    
  5. Reconfigure GitLab for the changes to take effect.
  6. Enable Monitoring

Please note:

  • If you want your database to listen on a specific interface, change the configuration: postgresql['listen_address'] = '0.0.0.0'.
  • If your PgBouncer service runs under a different user account, you also need to specify: postgresql['pgbouncer_user'] = PGBOUNCER_USERNAME in your configuration.

Enable Monitoring

Introduced in GitLab 12.0.

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

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

    # Enable service discovery for Prometheus
    consul['monitoring_service_discovery'] = true
    
    # Set the network addresses that the exporters will listen on
    node_exporter['listen_address'] = '0.0.0.0:9100'
    postgres_exporter['listen_address'] = '0.0.0.0:9187'
    
  2. Run sudo gitlab-ctl reconfigure to compile the configuration.

Database nodes post-configuration

Primary node

Select one node as a primary node.

  1. Open a database prompt:

    gitlab-psql -d gitlabhq_production
    
  2. Enable the pg_trgm extension:

    CREATE EXTENSION pg_trgm;
    
  3. Enable the btree_gist extension:

    CREATE EXTENSION btree_gist;
    
  4. Exit the database prompt by typing \q and Enter.

  5. Verify the cluster is initialized with one node:

    gitlab-ctl repmgr cluster show
    

    The output should be similar to the following:

    Role      | Name     | Upstream | Connection String
    ----------+----------|----------|----------------------------------------
    * master  | HOSTNAME |          | host=HOSTNAME user=gitlab_repmgr dbname=gitlab_repmgr
    
  6. Note down the hostname or IP address in the connection string: host=HOSTNAME. We will refer to the hostname in the next section as MASTER_NODE_NAME. If the value is not an IP address, it will need to be a resolvable name (via DNS or /etc/hosts)

Secondary nodes
  1. Set up the repmgr standby:

    gitlab-ctl repmgr standby setup MASTER_NODE_NAME
    

    Do note that this will remove the existing data on the node. The command has a wait time.

    The output should be similar to the following:

    # gitlab-ctl repmgr standby setup MASTER_NODE_NAME
    Doing this will delete the entire contents of /var/opt/gitlab/postgresql/data
    If this is not what you want, hit Ctrl-C now to exit
    To skip waiting, rerun with the -w option
    Sleeping for 30 seconds
    Stopping the database
    Removing the data
    Cloning the data
    Starting the database
    Registering the node with the cluster
    ok: run: repmgrd: (pid 19068) 0s
    
  2. Verify the node now appears in the cluster:

    gitlab-ctl repmgr cluster show
    

    The output should be similar to the following:

    Role      | Name    | Upstream  | Connection String
    ----------+---------|-----------|------------------------------------------------
    * master  | MASTER  |           | host=MASTER_NODE_NAME user=gitlab_repmgr dbname=gitlab_repmgr
      standby | STANDBY | MASTER    | host=STANDBY_HOSTNAME user=gitlab_repmgr dbname=gitlab_repmgr
    

Repeat the above steps on all secondary nodes.

Database checkpoint

Before moving on, make sure the databases are configured correctly. Run the following command on the primary node to verify that replication is working properly:

gitlab-ctl repmgr cluster show

The output should be similar to:

Role      | Name         | Upstream     | Connection String
----------+--------------|--------------|--------------------------------------------------------------------
* master  | MASTER  |        | host=MASTER port=5432 user=gitlab_repmgr dbname=gitlab_repmgr
  standby | STANDBY | MASTER | host=STANDBY port=5432 user=gitlab_repmgr dbname=gitlab_repmgr

If the ‘Role’ column for any node says “FAILED”, check the Troubleshooting section before proceeding.

Also, check that the check master command works successfully on each node:

su - gitlab-consul
gitlab-ctl repmgr-check-master || echo 'This node is a standby repmgr node'

This command relies on exit codes to tell Consul whether a particular node is a master or secondary. The most important thing here is that this command does not produce errors. If there are errors it’s most likely due to incorrect gitlab-consul database user permissions. Check the Troubleshooting section before proceeding.

Configuring the PgBouncer node

  1. Make sure you collect CONSUL_SERVER_NODES, CONSUL_PASSWORD_HASH, and PGBOUNCER_PASSWORD_HASH before executing the next step.

  2. One each node, edit the /etc/gitlab/gitlab.rb config file and replace values noted in the # START user configuration section as below:

    # Disable all components except PgBouncer and Consul agent
    roles ['pgbouncer_role']
    
    # Configure PgBouncer
    pgbouncer['admin_users'] = %w(pgbouncer gitlab-consul)
    
    # Configure Consul agent
    consul['watchers'] = %w(postgresql)
    
    # START user configuration
    # Please set the real values as explained in Required Information section
    # Replace CONSUL_PASSWORD_HASH with with a generated md5 value
    # Replace PGBOUNCER_PASSWORD_HASH with with a generated md5 value
    pgbouncer['users'] = {
      'gitlab-consul': {
        password: 'CONSUL_PASSWORD_HASH'
      },
      'pgbouncer': {
        password: 'PGBOUNCER_PASSWORD_HASH'
      }
    }
    # Replace placeholders:
    #
    # Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z
    # with the addresses gathered for CONSUL_SERVER_NODES
    consul['configuration'] = {
      retry_join: %w(Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z)
    }
    #
    # END user configuration
    
    Note: pgbouncer_role was introduced with GitLab 10.3.
  3. Run gitlab-ctl reconfigure

  4. Create a .pgpass file so Consul is able to reload PgBouncer. Enter the PGBOUNCER_PASSWORD twice when asked:

    gitlab-ctl write-pgpass --host 127.0.0.1 --database pgbouncer --user pgbouncer --hostuser gitlab-consul
    
  5. Enable monitoring

PgBouncer Checkpoint

  1. Ensure each node is talking to the current master:

    gitlab-ctl pgb-console # You will be prompted for PGBOUNCER_PASSWORD
    

    If there is an error psql: ERROR: Auth failed after typing in the password, ensure you previously generated the MD5 password hashes with the correct format. The correct format is to concatenate the password and the username: PASSWORDUSERNAME. For example, Sup3rS3cr3tpgbouncer would be the text needed to generate an MD5 password hash for the pgbouncer user.

  2. Once the console prompt is available, run the following queries:

    show databases ; show clients ;
    

    The output should be similar to the following:

            name         |  host       | port |      database       | force_user | pool_size | reserve_pool | pool_mode | max_connections | current_connections
    ---------------------+-------------+------+---------------------+------------+-----------+--------------+-----------+-----------------+---------------------
     gitlabhq_production | MASTER_HOST | 5432 | gitlabhq_production |            |        20 |            0 |           |               0 |                   0
     pgbouncer           |             | 6432 | pgbouncer           | pgbouncer  |         2 |            0 | statement |               0 |                   0
    (2 rows)
    
     type |   user    |      database       |  state  |   addr         | port  | local_addr | local_port |    connect_time     |    request_time     |    ptr    | link | remote_pid | tls
    ------+-----------+---------------------+---------+----------------+-------+------------+------------+---------------------+---------------------+-----------+------+------------+-----
     C    | pgbouncer | pgbouncer           | active  | 127.0.0.1      | 56846 | 127.0.0.1  |       6432 | 2017-08-21 18:09:59 | 2017-08-21 18:10:48 | 0x22b3880 |      |          0 |
    (2 rows)
    

Configure the internal load balancer

If you’re running more than one PgBouncer node as recommended, then at this time you’ll need to set up a TCP internal load balancer to serve each correctly. This can be done with any reputable TCP load balancer.

As an example here’s how you could do it with HAProxy:

global
    log /dev/log local0
    log localhost local1 notice
    log stdout format raw local0

defaults
    log global
    default-server inter 10s fall 3 rise 2
    balance leastconn

frontend internal-pgbouncer-tcp-in
    bind *:6432
    mode tcp
    option tcplog

    default_backend pgbouncer

backend pgbouncer
    mode tcp
    option tcp-check

    server pgbouncer1 <ip>:6432 check
    server pgbouncer2 <ip>:6432 check
    server pgbouncer3 <ip>:6432 check

Refer to your preferred Load Balancer’s documentation for further guidance.

Configuring the Application nodes

These will be the nodes running the gitlab-rails service. You may have other attributes set, but the following need to be set.

  1. Edit /etc/gitlab/gitlab.rb:

    # Disable PostgreSQL on the application node
    postgresql['enable'] = false
    
    gitlab_rails['db_host'] = 'PGBOUNCER_NODE' or 'INTERNAL_LOAD_BALANCER'
    gitlab_rails['db_port'] = 6432
    gitlab_rails['db_password'] = 'POSTGRESQL_USER_PASSWORD'
    gitlab_rails['auto_migrate'] = false
    
  2. Reconfigure GitLab for the changes to take effect.

Application node post-configuration

Ensure that all migrations ran:

gitlab-rake gitlab:db:configure

Note: If you encounter a rake aborted! error stating that PgBouncer is failing to connect to PostgreSQL it may be that your PgBouncer node’s IP address is missing from PostgreSQL’s trust_auth_cidr_addresses in gitlab.rb on your database nodes. See PgBouncer error ERROR: pgbouncer cannot connect to server in the Troubleshooting section before proceeding.

Ensure GitLab is running

At this point, your GitLab instance should be up and running. Verify you are able to login, and create issues and merge requests. If you have troubles check the Troubleshooting section.

Example configuration

Here we’ll show you some fully expanded example configurations.

This example uses 3 Consul servers, 3 PgBouncer servers (with associated internal load balancer), 3 PostgreSQL servers, and 1 application node.

We start with all servers on the same 10.6.0.0/16 private network range, they can connect to each freely other on those addresses.

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

  • 10.6.0.11: Consul 1
  • 10.6.0.12: Consul 2
  • 10.6.0.13: Consul 3
  • 10.6.0.20: Internal Load Balancer
  • 10.6.0.21: PgBouncer 1
  • 10.6.0.22: PgBouncer 2
  • 10.6.0.23: PgBouncer 3
  • 10.6.0.31: PostgreSQL master
  • 10.6.0.32: PostgreSQL secondary
  • 10.6.0.33: PostgreSQL secondary
  • 10.6.0.41: GitLab application

All passwords are set to toomanysecrets, please do not use this password or derived hashes and the external_url for GitLab is http://gitlab.example.com.

Please note that after the initial configuration, if a failover occurs, the PostgresSQL master will change to one of the available secondaries until it is failed back.

On each server edit /etc/gitlab/gitlab.rb:

# Disable all components except Consul
roles ['consul_role']

consul['configuration'] = {
  server: true,
  retry_join: %w(10.6.0.11 10.6.0.12 10.6.0.13)
}
consul['monitoring_service_discovery'] =  true

Reconfigure Omnibus GitLab for the changes to take effect.

On each server edit /etc/gitlab/gitlab.rb:

# Disable all components except Pgbouncer and Consul agent
roles ['pgbouncer_role']

# Configure PgBouncer
pgbouncer['admin_users'] = %w(pgbouncer gitlab-consul)

pgbouncer['users'] = {
  'gitlab-consul': {
    password: '5e0e3263571e3704ad655076301d6ebe'
  },
  'pgbouncer': {
    password: '771a8625958a529132abe6f1a4acb19c'
  }
}

consul['watchers'] = %w(postgresql)
consul['enable'] = true
consul['configuration'] = {
  retry_join: %w(10.6.0.11 10.6.0.12 10.6.0.13)
}
consul['monitoring_service_discovery'] =  true

Reconfigure Omnibus GitLab for the changes to take effect.

Internal load balancer setup

An internal load balancer (TCP) is then required to be setup to serve each PgBouncer node (in this example on the IP of 10.6.0.20). An example of how to do this can be found in the PgBouncer Configure Internal Load Balancer section.

Primary node

On primary node edit /etc/gitlab/gitlab.rb:

# Disable all components except PostgreSQL and Repmgr and Consul
roles ['postgres_role']

# PostgreSQL configuration
postgresql['listen_address'] = '0.0.0.0'
postgresql['hot_standby'] = 'on'
postgresql['wal_level'] = 'replica'
postgresql['shared_preload_libraries'] = 'repmgr_funcs'

# Disable automatic database migrations
gitlab_rails['auto_migrate'] = false

postgresql['pgbouncer_user_password'] = '771a8625958a529132abe6f1a4acb19c'
postgresql['sql_user_password'] = '450409b85a0223a214b5fb1484f34d0f'
postgresql['max_wal_senders'] = 4

postgresql['trust_auth_cidr_addresses'] = %w(10.6.0.0/16)
repmgr['trust_auth_cidr_addresses'] = %w(10.6.0.0/16)

# Configure the Consul agent
consul['services'] = %w(postgresql)
consul['enable'] = true
consul['configuration'] = {
  retry_join: %w(10.6.0.11 10.6.0.12 10.6.0.13)
}
consul['monitoring_service_discovery'] =  true

Reconfigure Omnibus GitLab for the changes to take effect.

Secondary nodes

On secondary nodes, edit /etc/gitlab/gitlab.rb and add all the configuration added to primary node, noted above. In addition, append the following configuration:

# Specify if a node should attempt to be master on initialization
repmgr['master_on_initialization'] = false

Reconfigure Omnibus GitLab for the changes to take effect.

On the server edit /etc/gitlab/gitlab.rb:

external_url 'http://gitlab.example.com'

gitlab_rails['db_host'] = '10.6.0.20' # Internal Load Balancer for PgBouncer nodes
gitlab_rails['db_port'] = 6432
gitlab_rails['db_password'] = 'toomanysecrets'
gitlab_rails['auto_migrate'] = false

postgresql['enable'] = false
pgbouncer['enable'] = false
consul['enable'] = true

# Configure Consul agent
consul['watchers'] = %w(postgresql)

pgbouncer['users'] = {
  'gitlab-consul': {
    password: '5e0e3263571e3704ad655076301d6ebe'
  },
  'pgbouncer': {
    password: '771a8625958a529132abe6f1a4acb19c'
  }
}

consul['configuration'] = {
  retry_join: %w(10.6.0.11 10.6.0.12 10.6.0.13)
}

Reconfigure Omnibus GitLab for the changes to take effect.

After deploying the configuration follow these steps:

  1. On 10.6.0.31, our primary database:

    Enable the pg_trgm and btree_gist extensions:

    gitlab-psql -d gitlabhq_production
    
    CREATE EXTENSION pg_trgm;
    CREATE EXTENSION btree_gist;
    
  2. On 10.6.0.32, our first standby database:

    Make this node a standby of the primary:

    gitlab-ctl repmgr standby setup 10.6.0.21
    
  3. On 10.6.0.33, our second standby database:

    Make this node a standby of the primary:

    gitlab-ctl repmgr standby setup 10.6.0.21
    
  4. On 10.6.0.41, our application server:

    Set gitlab-consul user’s PgBouncer password to toomanysecrets:

    gitlab-ctl write-pgpass --host 127.0.0.1 --database pgbouncer --user pgbouncer --hostuser gitlab-consul
    

    Run database migrations:

    gitlab-rake gitlab:db:configure
    

Example minimal setup

This example uses 3 PostgreSQL servers, and 1 application node (with PgBouncer setup alongside).

It differs from the recommended setup by moving the Consul servers into the same servers we use for PostgreSQL. The trade-off is between reducing server counts, against the increased operational complexity of needing to deal with PostgreSQL failover and restore procedures in addition to Consul outage recovery on the same set of machines.

In this example we start with all servers on the same 10.6.0.0/16 private network range, they can connect to each freely other on those addresses.

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

  • 10.6.0.21: PostgreSQL master
  • 10.6.0.22: PostgreSQL secondary
  • 10.6.0.23: PostgreSQL secondary
  • 10.6.0.31: GitLab application

All passwords are set to toomanysecrets, please do not use this password or derived hashes.

The external_url for GitLab is http://gitlab.example.com

Please note that after the initial configuration, if a failover occurs, the PostgresSQL master will change to one of the available secondaries until it is failed back.

Example minimal configuration for database servers

Primary node

On primary database node edit /etc/gitlab/gitlab.rb:

# Disable all components except PostgreSQL, Repmgr, and Consul
roles ['postgres_role']

# PostgreSQL configuration
postgresql['listen_address'] = '0.0.0.0'
postgresql['hot_standby'] = 'on'
postgresql['wal_level'] = 'replica'
postgresql['shared_preload_libraries'] = 'repmgr_funcs'

# Disable automatic database migrations
gitlab_rails['auto_migrate'] = false

# Configure the Consul agent
consul['services'] = %w(postgresql)

postgresql['pgbouncer_user_password'] = '771a8625958a529132abe6f1a4acb19c'
postgresql['sql_user_password'] = '450409b85a0223a214b5fb1484f34d0f'
postgresql['max_wal_senders'] = 4

postgresql['trust_auth_cidr_addresses'] = %w(10.6.0.0/16)
repmgr['trust_auth_cidr_addresses'] = %w(10.6.0.0/16)

consul['configuration'] = {
  server: true,
  retry_join: %w(10.6.0.21 10.6.0.22 10.6.0.23)
}

Reconfigure Omnibus GitLab for the changes to take effect.

Secondary nodes

On secondary nodes, edit /etc/gitlab/gitlab.rb and add all the information added to primary node, noted above. In addition, append the following configuration

# Specify if a node should attempt to be master on initialization
repmgr['master_on_initialization'] = false

Example minimal configuration for application server

On the server edit /etc/gitlab/gitlab.rb:

external_url 'http://gitlab.example.com'

gitlab_rails['db_host'] = '127.0.0.1'
gitlab_rails['db_port'] = 6432
gitlab_rails['db_password'] = 'toomanysecrets'
gitlab_rails['auto_migrate'] = false

postgresql['enable'] = false
pgbouncer['enable'] = true
consul['enable'] = true

# Configure PgBouncer
pgbouncer['admin_users'] = %w(pgbouncer gitlab-consul)

# Configure Consul agent
consul['watchers'] = %w(postgresql)

pgbouncer['users'] = {
  'gitlab-consul': {
    password: '5e0e3263571e3704ad655076301d6ebe'
  },
  'pgbouncer': {
    password: '771a8625958a529132abe6f1a4acb19c'
  }
}

consul['configuration'] = {
  retry_join: %w(10.6.0.21 10.6.0.22 10.6.0.23)
}

Reconfigure Omnibus GitLab for the changes to take effect.

Example minimal setup manual steps

The manual steps for this configuration are the same as for the example recommended setup.

Failover procedure

By default, if the master database fails, repmgrd should promote one of the standby nodes to master automatically, and Consul will update PgBouncer with the new master.

If you need to failover manually, you have two options:

Shutdown the current master database

Run:

gitlab-ctl stop postgresql

The automated failover process will see this and failover to one of the standby nodes.

Or perform a manual failover

  1. Ensure the old master node is not still active.
  2. Login to the server that should become the new master and run:

    gitlab-ctl repmgr standby promote
    
  3. If there are any other standby servers in the cluster, have them follow the new master server:

    gitlab-ctl repmgr standby follow NEW_MASTER
    

Restore procedure

If a node fails, it can be removed from the cluster, or added back as a standby after it has been restored to service.

Remove a standby from the cluster

From any other node in the cluster, run:

  gitlab-ctl repmgr standby unregister --node=X

where X is the value of node in repmgr.conf on the old server.

To find this, you can use:

  awk -F = '$1 == "node" { print $2 }' /var/opt/gitlab/postgresql/repmgr.conf

It will output something like:

  959789412

Then you will use this ID to unregister the node:

  gitlab-ctl repmgr standby unregister --node=959789412

Add a node as a standby server

From the standby node, run:

  gitlab-ctl repmgr standby follow NEW_MASTER
  gitlab-ctl restart repmgrd
Warning: When the server is brought back online, and before you switch it to a standby node, repmgr will report that there are two masters. If there are any clients that are still attempting to write to the old master, this will cause a split, and the old master will need to be resynced from scratch by performing a gitlab-ctl repmgr standby setup NEW_MASTER.

Add a failed master back into the cluster as a standby node

Once repmgrd and PostgreSQL are running, the node will need to follow the new as a standby node.

  gitlab-ctl repmgr standby follow NEW_MASTER

Once the node is following the new master as a standby, the node needs to be unregistered from the cluster on the new master node.

Once the old master node has been unregistered from the cluster, it will need to be setup as a new standby:

  gitlab-ctl repmgr standby setup NEW_MASTER

Failure to unregister and read the old master node can lead to subsequent failovers not working.

Alternate configurations

Database authorization

By default, we give any host on the database network the permission to perform repmgr operations using PostgreSQL’s trust method. If you do not want this level of trust, there are alternatives.

You can trust only the specific nodes that will be database clusters, or you can require md5 authentication.

Trust specific addresses

If you know the IP address, or FQDN of all database and PgBouncer nodes in the cluster, you can trust only those nodes.

In /etc/gitlab/gitlab.rb on all of the database nodes, set repmgr['trust_auth_cidr_addresses'] to an array of strings containing all of the addresses.

If setting to a node’s FQDN, they must have a corresponding PTR record in DNS. If setting to a node’s IP address, specify it as XXX.XXX.XXX.XXX/32.

For example:

repmgr['trust_auth_cidr_addresses'] = %w(192.168.1.44/32 db2.example.com)

MD5 Authentication

If you are running on an untrusted network, repmgr can use md5 authentication with a .pgpass file to authenticate.

You can specify by IP address, FQDN, or by subnet, using the same format as in the previous section:

  1. On the current master node, create a password for the gitlab and gitlab_repmgr user:

    gitlab-psql -d template1
    template1=# \password gitlab_repmgr
    Enter password: ****
    Confirm password: ****
    template1=# \password gitlab
    
  2. On each database node:

    1. Edit /etc/gitlab/gitlab.rb:
      1. Ensure repmgr['trust_auth_cidr_addresses'] is not set
      2. Set postgresql['md5_auth_cidr_addresses'] to the desired value
      3. Set postgresql['sql_replication_user'] = 'gitlab_repmgr'
      4. Reconfigure with gitlab-ctl reconfigure
      5. Restart PostgreSQL with gitlab-ctl restart postgresql
    2. Create a .pgpass file. Enter the gitlab_repmgr password twice to when asked:

      gitlab-ctl write-pgpass --user gitlab_repmgr --hostuser gitlab-psql --database '*'
      
  3. On each PgBouncer node, edit /etc/gitlab/gitlab.rb:

    1. Ensure gitlab_rails['db_password'] is set to the plaintext password for the gitlab database user
    2. Reconfigure GitLab for the changes to take effect

Troubleshooting

Consul and PostgreSQL changes not taking effect

Due to the potential impacts, gitlab-ctl reconfigure only reloads Consul and PostgreSQL, it will not restart the services. However, not all changes can be activated by reloading.

To restart either service, run gitlab-ctl restart SERVICE

For PostgreSQL, it is usually safe to restart the master node by default. Automatic failover defaults to a 1 minute timeout. Provided the database returns before then, nothing else needs to be done. To be safe, you can stop repmgrd on the standby nodes first with gitlab-ctl stop repmgrd, then start afterwards with gitlab-ctl start repmgrd.

On the Consul server nodes, it is important to restart the Consul service in a controlled manner.

gitlab-ctl repmgr-check-master command produces errors

If this command displays errors about database permissions it is likely that something failed during install, resulting in the gitlab-consul database user getting incorrect permissions. Follow these steps to fix the problem:

  1. On the master database node, connect to the database prompt - gitlab-psql -d template1
  2. Delete the gitlab-consul user - DROP USER "gitlab-consul";
  3. Exit the database prompt - \q
  4. Reconfigure GitLab and the user will be re-added with the proper permissions.
  5. Change to the gitlab-consul user - su - gitlab-consul
  6. Try the check command again - gitlab-ctl repmgr-check-master.

Now there should not be errors. If errors still occur then there is another problem.

PgBouncer error ERROR: pgbouncer cannot connect to server

You may get this error when running gitlab-rake gitlab:db:configure or you may see the error in the PgBouncer log file.

PG::ConnectionBad: ERROR:  pgbouncer cannot connect to server

The problem may be that your PgBouncer node’s IP address is not included in the trust_auth_cidr_addresses setting in /etc/gitlab/gitlab.rb on the database nodes.

You can confirm that this is the issue by checking the PostgreSQL log on the master database node. If you see the following error then trust_auth_cidr_addresses is the problem.

2018-03-29_13:59:12.11776 FATAL:  no pg_hba.conf entry for host "123.123.123.123", user "pgbouncer", database "gitlabhq_production", SSL off

To fix the problem, add the IP address to /etc/gitlab/gitlab.rb.

postgresql['trust_auth_cidr_addresses'] = %w(123.123.123.123/32 <other_cidrs>)

Reconfigure GitLab for the changes to take effect.

Issues with other components

If you’re running into an issue with a component not outlined here, be sure to check the troubleshooting section of their specific documentation page:

Patroni

Note: Starting from GitLab 13.1, Patroni is available for experimental use to replace repmgr. Due to its experimental nature, Patroni support is subject to change without notice.

Patroni is an opinionated solution for PostgreSQL high-availability. It takes the control of PostgreSQL, overrides its configuration and manages its lifecycle (start, stop, restart). This is a more active approach when compared to repmgr. Both repmgr and Patroni are both supported and available. But Patroni will be the default (and perhaps the only) option for PostgreSQL 12 clustering and cascading replication for Geo deployments.

The architecture (that was mentioned above) does not change for Patroni. You do not need any special consideration for Patroni while provisioning your database nodes. Patroni heavily relies on Consul to store the state of the cluster and elect a leader. Any failure in Consul cluster and its leader election will propagate to Patroni cluster as well.

Similar to repmgr, Patroni monitors the cluster and handles failover. When the primary node fails it works with Consul to notify PgBouncer. However, as opposed to repmgr, on failure, Patroni handles the transitioning of the old primary to a replica and rejoins it to the cluster automatically. So you do not need any manual operation for recovering the cluster as you do with repmgr.

With Patroni the connection flow is slightly different. Patroni on each node connects to Consul agent to join the cluster. Only after this point it decides if the node is the primary or a replica. Based on this decision, it configures and starts PostgreSQL which it communicates with directly over a Unix socket. This implies that if Consul cluster is not functional or does not have a leader, Patroni and by extension PostgreSQL will not start. Patroni also exposes a REST API which can be accessed via its default port on each node.

Configuring Patroni cluster

You must enable Patroni explicitly to be able to use it (with patroni['enable'] = true). When Patroni is enabled repmgr will be disabled automatically.

Any PostgreSQL configuration item that controls replication, for example wal_level, max_wal_senders, etc, are strictly controlled by Patroni and will override the original settings that you make with the postgresql[...] configuration key. Hence, they are all separated and placed under patroni['postgresql'][...]. This behavior is limited to replication. Patroni honours any other PostgreSQL configuration that was made with the postgresql[...] configuration key. For example, max_wal_senders by default is set to 5. If you wish to change this you must set it with the patroni['postgresql']['max_wal_senders'] configuration key.

The configuration of Patroni node is very similar to a repmgr but shorter. When Patroni is enabled, first you can ignore any replication setting of PostgreSQL (it will be overwritten anyway). Then you can remove any repmgr[...] or repmgr-specific configuration as well. Especially, make sure that you remove postgresql['shared_preload_libraries'] = 'repmgr_funcs'.

Here is an example similar to the one that was done with repmgr:

# Disable all components except PostgreSQL and Repmgr and Consul
roles['postgres_role']

# Enable Patroni
patroni['enable'] = true

# PostgreSQL configuration
postgresql['listen_address'] = '0.0.0.0'

# Disable automatic database migrations
gitlab_rails['auto_migrate'] = false

# Configure the Consul agent
consul['services'] = %w(postgresql)

# START user configuration
# Please set the real values as explained in Required Information section
#
# Replace PGBOUNCER_PASSWORD_HASH with a generated md5 value
postgresql['pgbouncer_user_password'] = 'PGBOUNCER_PASSWORD_HASH'
# Replace POSTGRESQL_PASSWORD_HASH with a generated md5 value
postgresql['sql_user_password'] = 'POSTGRESQL_PASSWORD_HASH'

# Replace X with value of number of db nodes + 1 (OPTIONAL the default value is 5)
patroni['postgresql']['max_wal_senders'] = X
patroni['postgresql']['max_replication_slots'] = X

# Replace XXX.XXX.XXX.XXX/YY with Network Address
postgresql['trust_auth_cidr_addresses'] = %w(XXX.XXX.XXX.XXX/YY)

# Replace placeholders:
#
# Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z
# with the addresses gathered for CONSUL_SERVER_NODES
consul['configuration'] = {
  retry_join: %w(Y.Y.Y.Y consul1.gitlab.example.com Z.Z.Z.Z)
}
#
# END user configuration

You do not need an additional or different configuration for replica nodes. As a matter of fact, you don’t have to have a predetermined primary node. Therefore all database nodes use the same configuration.

Once the configuration of a node is done, you must reconfigure Omnibus GitLab on each node for the changes to take effect.

Generally, when Consul cluster is ready, the first node that reconfigures becomes the leader. You do not need to sequence the nodes reconfiguration. You can run them in parallel or in any order. If you choose an arbitrary order you do not have any predetermined master.

As opposed to repmgr, once the nodes are reconfigured you do not need any further action or additional command to join the replicas.

Database authorization for Patroni

Patroni uses Unix socket to manage PostgreSQL instance. Therefore, the connection from the local socket must be trusted.

Also, replicas use the replication user (gitlab_replicator by default) to communicate with the leader. For this user, you can choose between trust and md5 authentication. If you set postgresql['sql_replication_password'], Patroni will use md5 authentication, otherwise it falls back to trust. You must to specify the cluster CIDR in postgresql['md5_auth_cidr_addresses'] or postgresql['trust_auth_cidr_addresses'] respectively.

Interacting with Patroni cluster

You can use gitlab-ctl patroni members to check the status of the cluster members. To check the status of each node gitlab-ctl patroni provides two additional sub-commands, check-leader and check-replica which indicate if a node is the primary or a replica.

When Patroni is enabled, you don’t have direct control over postgresql service. Patroni will signal PostgreSQL’s startup, shutdown, and restart. For example, for shutting down PostgreSQL on a node, you must shutdown Patroni on the same node with:

sudo gitlab-ctl stop patroni

Manual failover procedure for Patroni

While Patroni supports automatic failover, you also have the ability to perform a manual one, where you have two slightly different options:

  • Failover: allows you to perform a manual failover when there are no healthy nodes. You can perform this action in any PostgreSQL node:

    sudo gitlab-ctl patroni failover
    
  • Switchover: only works when the cluster is healthy and allows you to schedule a switchover (it can happen immediately). You can perform this action in any PostgreSQL node:

    sudo gitlab-ctl patroni switchover
    

For further details on this subject, see the Patroni documentation.

Recovering the Patroni cluster

To recover the old primary and rejoin it to the cluster as a replica, you can simply start Patroni with:

sudo gitlab-ctl start patroni

No further configuration or intervention is needed.

Maintenance procedure for Patroni

With Patroni enabled, you can run a planned maintenance. If you want to do some maintenance work on one node and you don’t want Patroni to manage it, you can use put it into maintenance mode:

sudo gitlab-ctl patroni pause

When Patroni runs in a paused mode, it does not change the state of PostgreSQL. Once you are done you can resume Patroni:

sudo gitlab-ctl patroni resume

For further details, see Patroni documentation on this subject.

Switching from repmgr to Patroni

Warning: Although switching from repmgr to Patroni is fairly straightforward the other way around is not. Rolling back from Patroni to repmgr can be complicated and may involve deletion of data directory. If you need to do that, please contact GitLab support.

You can switch an exiting database cluster to use Patroni instead of repmgr with the following steps:

  1. Stop repmgr on all replica nodes and lastly with the primary node:

    sudo gitlab-ctl stop repmgrd
    
  2. Stop PostgreSQL on all replica nodes:

    sudo gitlab-ctl stop postgresql
    
    Note: Ensure that there is no walsender process running on the primary node. ps aux | grep walsender must not show any running process.
  3. On the primary node, configure Patroni. Remove repmgr and any other repmgr-specific configuration. Also remove any configuration that is related to PostgreSQL replication.
  4. Reconfigure Omnibus GitLab on the primary node. It will become the leader. You can check this with:

    sudo gitlab-ctl tail patroni
    
  5. Repeat the last two steps for all replica nodes. gitlab.rb should look the same on all nodes.
  6. Optional: You can remove gitlab_repmgr database and role on the primary.