Backing up PostgreSQL databases with Barman

Barman is an open-source administration tool designed for PostgreSQL server disaster recovery. Developed in Python, Barman offers the capability to efficiently conduct remote backups across multiple servers in diverse business environments.

Setting itself apart with its unique methodology, Barman uses PostgreSQL logs for backup creation, offering a sophisticated alternative to traditional SQL dump processes.

Before you start

To complete the actions presented below, you must have:

• A Scaleway account logged into the console
• Owner status or IAM permissions allowing you to perform actions in the intended Organization
• An SSH key
• Two Instances running a PostgreSQL database on Ubuntu Bionic or a later version
• sudo privileges or access to the root user

Installing Barman

As you will back up your databases with Barman, it is recommended to host the application on a different instance than your databases. Ideally in a geographically distant data center. In this tutorial, we install Barman on a second server to migrate the database from one to the other server for backup and redundancy purposes.

Barman is available in the official APT repositories of Ubuntu. Connect to the second server, called pgsql-backup and install the tool:

1. Update the APT package cache and upgrade the already installed packages to their latest version:
   sudo apt-get update && sudo apt-get upgrade -y

2. Install Barman:
   sudo apt-get install barman

Configuring Barman

For Barman to copy data between the two servers, some pre-work is required:

Creating a dedicated PostgreSQL user on pgsql

As Barman has been installed on the second server (pgsql-backup), it is required to create a database user for the tool on the first server (pgsql).

1. Connect on the server pgsql and log into the postgres account:

   sudo -i -u postgres

2. Create the user and enter twice the desired password. When asked if the account should have superuser privileges, type y and press Enter:

   createuser --interactive -P barman

3. Enable the connection to the server from pgsql-backup by editing the file /etc/postgresql/9.5/postgresql.conf. Change the value of listen_addresses to the new server, or use an asterisk to enable the connection from any IP.

   listen_addresses = 'localhost, pgsql-backup'

   Note

   Note that the path to the postgresql.conf depends on your PostgreSQL version. Edit 9.5 to the corresponding version number of your PostgreSQL installation.

4. Restart the service

   sudo service postgresql restart

   Test the connection from pgsql-backup by running an SQL query:

   psql -c 'SELECT version()' -U barman -h pgsql postgres

Creating the .pgpass file on pgsql-backup

During the installation of Barman on the server pgsql-backup, a system user account called barman was created.

1. Set a password for the user:

   sudo passwd barman

2. Enter the user account:

   sudo -i -u barman

3. Create the .pgpass file for the barman user:

   echo "pgsql:5432:*:barman:password" >> ~/.pgpass

   Note

   The data format for the .pgpass file is hostname:port:database:username:password. If an asterisk is used in any of the first four fields, it will correspond to everything. The username refers to the PostgreSQL user that was created previously, not to the Linux user account. You may refer to the official documentation for more information about this file.

   The file .pgpass in a user's home directory can contain passwords to be used if the connection requires a password (and no password has been specified otherwise).

Setting up key-based authentication

To perform backups without manual authentication, generate an SSH key that will be used for authentication:

To perform backups without user intervention, we need to set up and copy SSH keys for passwordless authentication. Barman makes use of this method to copy data through rsync.

1. Connect to the server pgsql-backup, switch to user barman, and generate the keys

   ssh-keygen -t rsa

2. Copy the key to the user account postgres on pgsql:

   ssh-copy-id postgres@pgsql

   The following message will appear if the transfer of the key has been successful:

   Number of key(s) added: 1
   
   Now try logging into the machine, with:   "ssh 'postgres@pgsql'"
   and check to make sure that only the key(s) you wanted were added.

3. Barman also requires access to the Postgres account on the server pgsql-backup. Copy the key into the directory of the postgres user and test the connection:

   ssh-copy-id postgres@localhost
   ssh postgres@localhost -C true

4. Once this is done, log in as postgres user on pgsql and generate an SSH key:

   ssh-keygen -t rsa

5. Copy the generated key to the list of authorized keys of the user barman on pgsql-backup:

   ssh-copy-id barman@pgsql-backup

6. Test the connection to the server:

   ssh barman@pgsql-backup -C true

Configuring Barman

The configuration of Barman is done on the server pgsql-backup.

1. Create the directory /etc/barman.d:

   mkdir /etc/barman.d

2. Open the file /etc/barman.conf and remove the leading semicolon (;) from the following line:

   ;configuration_files_directory = /etc/barman.d

3. Enter the directory /etc/barman.d and create a file pgsql.conf with the following content:

   [pgsql]
   description =  "Old PostgreSQL server"
   conninfo = host=10.55.66.77 user=barman dbname=Our_Database
   ssh_command = ssh postgres@pgsql
   retention_policy = RECOVERY WINDOW OF 2 WEEKS

   The information in this file is self-explanatory. The retention_policy defines the time frame during which backups are kept. This can be set to your needs. For more information about this file, you may refer to the official documentation.

Configuring PostgreSQL

1. Connect to pgsql and add this line to the file /etc/postgresql/9.5/main/pg_hba.conf:

   host    all             all             10.55.66.88/32         trust

   Where 10.55.66.77 should be replaced with the IP of pgsql-backup.

2. Open the file /etc/postgresql/9.5/main/postgresql.conf and edit the values as shown:

   wal_level = archive
   archive_mode = on
   archive_command = 'rsync -a %p barman@10.55.66.77:/var/lib/barman/pgsql/incoming/%f'

3. Restart the PostgreSQL service:

   sudo systemctl restart postgresql

4. Check if the connection to the server pgsql works from Barman, by running the command barman check pgsql after logging into the barman user account on pgsql-backup:

   barman@pgsql-backup:~$ barman check pgsql
   Server pgsql:
       PostgreSQL: OK
       archive_mode: OK
       wal_level: OK
       archive_command: OK
       continuous archiving: OK
       directories: OK
       retention policy settings: OK
       backup maximum age: OK (no last_backup_maximum_age provided)
       compression settings: OK
       minimum redundancy requirements: OK (have 0 backups, expected at least 0)
       ssh: OK (PostgreSQL server)
       not in recovery: OK

If all values are OK, you are ready to make your first backup.

Performing Backups

1. Start a backup with the command barman backup pgsql. You will see an output like the following:
   barman@pgsql-backup:~$ barman backup pgsql
   Starting backup for server pgsql in /var/lib/barman/pgsql/base/20180911T115925
   Backup start at xlog location: 0/2000028 (000000010000000000000002, 00000028)
   Copying files.
   Copy done.
   Asking PostgreSQL server to finalize the backup.
   Backup size: 20.7 MiB
   Backup end at xlog location: 0/20000C0 (000000010000000000000002, 000000C0)
   Backup completed

2. To view a list of all backups available of pgsql, use the command
   barman list-backup pgsql

3. To view the details about a backup, use the following command:
   barman show-backup pgsql backup_id

The backup_id is visible from the backup list and in the form like this example 20180911T115925.

Restoring Backups

It is possible to import the backup in the PostgreSQL server running on pgsql-backup.

1. Stop the PostgreSQL service:
   sudo systemctl stop postgresql

2. Load the backup into the database with the following command:
   barman recover --remote-ssh-command "ssh postgres@localhost" pgsql 20180911T115925 /var/lib/postgresql/9.5/main

You will see an output like the following:

Starting remote restore for server pgsql using backup 20180911T115925
Destination directory: /var/lib/postgresql/9.5/main
Copying the base backup.
Copying required WAL segments.
Generating archive status files
Your PostgreSQL server has been successfully prepared for recovery!

3. Once the backup has been imported, restart the PostgreSQL service:
   sudo systemctl start postgresql

Your database has now successfully migrated to your new database server.

Automatizing Backups

It is possible to run Barman automatically to back up the content of your database regularly. This can be done easily by setting up a cron job on pgsql-backup.

1. Switch into the barman user:
   sudo -i -u barman

2. Edit the crontab of the user:
   crontab -e

3. To run a backup daily at 3:30, add the following line to the crontab and save it:
   30 03 * * * /usr/bin/barman backup pgsql

For more information about Barman, refer to the official documentation.