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About Gabriel Canepa

Gabriel Canepa
Gabriel Canepa is a Linux Foundation Certified System Administrator (LFCS-1500-0576-0100) and web developer from Villa Mercedes, San Luis, Argentina. He works for a worldwide leading consumer product company and takes great pleasure in using FOSS tools to increase productivity in all areas of his daily work. When he's not typing commands or writing code or articles, he enjoys telling bedtime stories with his wife to his two little daughters and playing with them, the great pleasure of his life.

PostgreSQL backup, restore, and migration Tutorial

This article is part of our Academy Course titled PostgreSQL Database Tutorial.

In this course, we provide a compilation of PostgreSQL tutorials that will help you set up and run your own database management system. We cover a wide range of topics, from installation and configuration, to custom commands and datatypes. With our straightforward tutorials, you will be able to get your own projects up and running in minimum time. Check it out here!

Since hardware can fail and human error may occur, having frequent backups and knowing how to restore them are important skills that every system administrator should have. Additionally, you will need to know how to migrate PostgreSQL databases from one machine to another in case you purchase new, more powerful servers. Thus, in this tutorial we will discuss how to perform these critical operations using a test environment with two Ubuntu 16.04 (server edition) virtual machines. We will name these VMs newserver (192.168.0.54) and oldserver (192.168.0.55), where the same PostgreSQL version (9.5) has been installed on both. We assume we will migrate the World_db database on oldserver over to newserver.

1. Backup, restore, and migration strategies

Traditionally, PostgreSQL database administrators used shell scripts and cron jobs to back up their databases. Although this approach was considered efficient a decade (or so) ago, today there are tools that make this process hassle-free and easier to maintain. Among these tools, Barman (Backup and Recovery Manager), a Python-based open source solution developed and maintained by 2ndQuadrant (a firm that specializes in PostgreSQL services) stands out.

2. Installing Barman

More accurately, Barman is a backup, restore, and disaster recovery tool for PostgreSQL. We will install it on the virtual machine that we called newserver (192.168.0.54) to migrate the databases from oldserver (192.168.0.55).

That said, let’s install Barman:

sudo aptitude update && sudo aptitude install barman

Once the installation has completed successfully, proceed with the following steps.

Step 1 – Create a dedicated PostgreSQL user in oldserver

In order for barman (which has been installed in newserver) to communicate with the PostgreSQL instance running on oldserver, we need to create a dedicated database user. To do so, run the following command as postgres on oldserver and enter the desired password for the new database user. Also, when you’re prompted to confirm if the account should have superuser privileges, enter y and press Enter

createuser --interactive -P barman

Then test the connection from newserver. We will check the connection against the postgres database, but you can use other database (in that case, you’ll have to modify the SQL query inside single quotes):

psql -c 'SELECT version()' -U barman -h 192.168.0.55 postgres

Refer to Fig. 1 for details:

Creating a dedicated user account and testing the connection

Figure 1 – Creating a dedicated user account and testing the connection

Throughout this article, we will use the word Barman to refer to the program itself, whereas the all-lowercase barman will represent either the command associated with the program or an account.

Step 2 – Create the .pgpass file in newserver

As part of the installation of Barman on newserver, a Linux account called barman was created. To set its password, do

sudo passwd barman

and enter the desired password. Then, switch user to barman:

sudo -i -u barman

and create the .pgpass file for user barman:

echo "192.168.0.55:5432:*:barman:password" >> ~/.pgpass
The actual 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 match everything. Please note that username here represents the PostgreSQL user we created in Step 1, not the Linux account we just referred to. The official documentation for this file can be found here.

This file can contain passwords to be used if a connection requires one (in this case, barman will use it to talk to the PostgreSQL instance on oldserver).

Step 3 – Set up key-based authentication

In order to perform backups without user intervention we will need to set up and copy SSH keys for passwordless authentication. Barman will make use of this method to copy data through rsync.

On newserver, switch to user barman and generate the keys

ssh-keygen -t rsa

(choose the default destination file for the public key and an empty passphrase).

Next, copy the public key to the authorized keys of user postgres on oldserver:

ssh-copy-id postgres@192.168.0.55

This will allow barman on newserver to connect to oldserver as user postgres. To test if the connection can be made without password, as expected, you can run the following command (on success, it will not return anything):

ssh postgres@192.168.0.55 -C true

You’ll also need to allow barman to SSH into localhost as the local user postgres:

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

Finally, on oldserver log in as postgres and do

ssh-keygen -t rsa

and copy the resulting key to the list of authorized keys for user barman on newserver:

ssh-copy-id barman@192.168.0.54

Again, test the connection before proceeding:

ssh barman@192.168.0.54 -C true

Step 4 – Configure Barman

On newserver, open the Barman main configuration file (/etc/barman.conf) and uncomment this line by removing the leading semicolon:

;configuration_files_directory = /etc/barman.d

should read

configuration_files_directory = /etc/barman.d

(if /etc/barman.d does not exist, you’ll have to create it with mkdir /etc/barman.d)

And create a file named oldserver.conf with the following contents (the word inside square brackets represents the name that barman will use to identify the connection details):

[oldserver]
description =  "Our old PostgreSQL server"
conninfo = host=192.168.0.55 user=barman dbname=World_db
ssh_command = ssh postgres@192.168.0.55
retention_policy = RECOVERY WINDOW OF 2 WEEKS

where most variables are self-explanatory with the exception of retention_policy. This variable is used to determine for how long backups should be kept (2 weeks in this case). This should be modified based on the expected activity and growth of the database, and the available space on the filesystem where backups will be kept.

Step 5 – Configure PostgreSQL

On oldserver:

Add this line to /etc/postgresql/9.5/main/pg_hba.conf:

host    all             all             192.168.0.54/24         trust

Then make sure the following variables on /etc/postgresql/9.5/main/postgresql.conf have the indicated values:

wal_level = archive
archive_mode = on
archive_command = 'rsync -a %p barman@192.168.0.54:/var/lib/barman/oldserver/incoming/%f'
As you will probably guess, the directory in the rsync connection string represents the directory where the backup files for oldserver will be kept on newserver.

On newserver, make sure the following variable on /etc/postgresql/9.5/main/postgresql.conf has the indicated value:

data_directory = '/var/lib/postgresql/9.5/data'

If the directory called data does not exist under /var/lib/postgresql/9.5, create it before proceeding (that is where the data files will be stored on newserver)

Then restart the postgresql service to activate the latest changes:

sudo systemctl restart postgresql

Step 6 – Test the Barman configuration

Once PostgreSQL has been configured on oldserver to allow connections from newserver, we are ready to test the configuration. To do so, switch to user barman on newserver and do

barman check oldserver
barman list-server

The first command will check the SSH and PostgreSQL connections, whereas the second one will show the list of configured PostgreSQL servers we wish to back up.

The output should be as follows (see Fig. 2):

Checking the barman connection from newserver to oldserver

Figure 2 – Checking the barman connection from newserver to oldserver

Step 7 – Perform the backup

Once all of the items in the output of barman check oldserver return OK, we are ready to perform our first backup with the following command (see Fig. 3):

barman backup oldserver

The output should be similar to Fig. 3:

Creating our first backup with barman

Figure 3 – Creating our first backup with barman

Once the backup has completed we can identify it with the help of

barman list-backup oldserver

which will list all the backups we have performed for oldserver. To view details about a specific backup, we’ll use

barman show-backup oldserver backup_id

where backup_id is the backup identification (20161015T120420 in Fig. 4).

Checking backups

Figure 4 – Checking backups

Step 8 – Restore the backup on newserver

As we can see in Fig. 8, the World_db database can’t be found on newserver. To migrate a backup, we will stop the postgresql service

sudo systemctl stop postgresql

and run the following command as user barman:

barman recover --remote-ssh-command "ssh postgres@localhost" oldserver 20161015T142346 /var/lib/postgresql/9.5/data

Note how barman makes use of the SSH keys to connect as user postgres to localhost in order to load the backup with id 20161015T142346 to the data directory. The result is shown in Fig. 5:

Restoring a backup with barman

Figure 5 – Restoring a backup with barman

After the recovery or migration is complete, start the postgresql service with a user with sudo access

sudo systemctl start postgresql

and check the World_db database as user postgres:

sudo -i -u postgres
psql
\c World_db

Now let’s run queries against the database, as shown in Fig. 6:

Querying the database we migrated

Figure 6 – Querying the database we migrated

Congratulations! You have successfully set up a very effective method to back up, restore, and migrate PostgreSQL databases.

3. Automating backups

In order to automate the backup process, switch to user barman and open the crontab file:

sudo -i -u barman
crontab -e

Then add the following two lines in it in order to execute a backup of oldserver each day at 12:45 pm

45 12 * * * /usr/bin/barman backup oldserver

Please note that this is a basic Barman / PostgreSQL setup, so I strongly suggest to check the official Barman docs here.

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Stephen

Thank you for your tutorial. I have followed the steps and crosscheck with other tutorials but I am stuck testing the barman. barman@barman-backup-server:~$ barman list-server main-db-server – Our main PostgreSQL server (WARNING: disabled) standby-db-server – Standby DB Server barman@barman-backup-server:~$ barman list-server main-db-server – Our main PostgreSQL server (WARNING: disabled) standby-db-server – Standby DB Server barman@barman-backup-server:~$ barman check standby-db-server Server standby-db-server: WAL archive: FAILED (please make sure WAL shipping is setup) PostgreSQL: FAILED directories: OK retention policy settings: OK backup maximum age: FAILED (interval provided: 1 day, latest backup age: No available backups) compression settings: OK failed backups: OK (there are… Read more »

Prashant Bana
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Prashant Bana

After setting up barman i’m getting stuck at “Asking PostgreSQL server to finalise backup” . I’ve rechecked the wals incoming directory. Does the finalising takes some time or did something go wrong ? Any help will be much appreciated .