Streaming Backup With Fallback WAL Archiving in PostgreSQL

Streaming Backup With Fallback WAL Archiving in PostgreSQL

In previous blog we saw How To Configure Streaming Backup & WAL Streaming using BARMAN Click here to read more.


In this blog we will configure
WAL archiving via barman-wal-archive along with WAL Streaming  for more robust architecture in PostgreSQL.


This alternate approach requires:

1. An additional SSH connection that allows the postgres user on the PostgreSQL server to connect as barman user on the Barman server.
2. The archive_command in PostgreSQL be configured to ship WAL files to Barman Server.


From Barman 2.6, the recommended way to safely and reliably archive WAL files to Barman via archive_command is to use the barman-wal-archive command contained in the barman-cli package. We can also use rsync/SSH as in archive_command. But with rsync/SSH method there is no mechanism that guarantees that the content of the file is flushed and fsync-ed to disk on Barman Server.

Follow the below steps to Configure Streaming Backup With Fallback WAL Archiving


Follow the same steps as in the blog How To Configure Streaming Backup & WAL Streaming using BARMAN, Click here to read more from Step 1 to Step 6. Once Step 6 is done continue with the below steps.


Step 6.1. Set Password for OS Account barman: Use OS command passwd barman to reset barman OS account in Backup Server.

[root@test-machine01 tmp]# passwd barman
Changing password for user barman.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@test-machine01 tmp]#


Step 6.2. Set Password for OS Account postgres: Use OS command passwd postgres to reset postgres OS account in PostgreSQL Database Server.

[root@test-machine02 ~]# passwd postgres
Changing password for user postgres.
New password:
BAD PASSWORD: The password contains the user name in some form
Retype new password:
passwd: all authentication tokens updated successfully.
[root@test-machine02 ~]#


Step 6.3. Configure Passwordless Authentication in Barman Server: Use OS command ssh-keygen to generate public and private keys. Once keys are generated use OS command ssh-copy-id to transfer the public key to PostgreSQL Database Server.

[root@test-machine01 ~]# su - barman
Last login: Tue Jun 22 10:02:53 +03 2021 on pts/0
-bash-4.2$
-bash-4.2$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/var/lib/barman/.ssh/id_rsa):
Created directory '/var/lib/barman/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /var/lib/barman/.ssh/id_rsa.
Your public key has been saved in /var/lib/barman/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:fg8qzAkNeneq4qKoYRNJCTNP5+S7z4RQWXb889KpETA barman@test-machine01
The key's randomart image is:
+---[RSA 2048]----+
|+ . o o..        |
|.=.= + .E        |
| o. =    +       |
|. ....    +      |
| o...o  S  = .   |
|  o.ooo.. o +    |
|.o .o=.+. o+     |
|+.o  +*  o.o     |
|*o....o..   .    |
+----[SHA256]-----+
-bash-4.2$
-bash-4.2$ls -ltr .ssh
total 8
-rw-r--r--. 1 barman barman  403 Jun 22 10:12 id_rsa.pub
-rw-------. 1 barman barman 1675 Jun 22 10:12 id_rsa
-bash-4.2$
 
-bash-4.2$ ssh-copy-id -i ~/.ssh/id_rsa.pub postgres@test-machine02
/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/var/lib/barman/.ssh/id_rsa.pub"
The authenticity of host 'test-machine02 (192.168.114.176)' can't be established.
ECDSA key fingerprint is SHA256:NbJdl0Pi8lmjbKHbz7q0GgYAy++evY3rNH7gCupnx+c.
ECDSA key fingerprint is MD5:39:33:1f:a7:bb:09:ac:81:cc:ff:cc:18:46:ca:76:c1.
Are you sure you want to continue connecting (yes/no)? yes
/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
postgres@test-machine02's password:
 
Number of key(s) added: 1
 
Now try logging into the machine, with:   "ssh 'postgres@test-machine02'"
and check to make sure that only the key(s) you wanted were added.
 
-bash-4.2$
-bash-4.2$ ssh 'postgres@test-machine02'
Last login: Tue Jun 22 10:30:29 2021
-bash-4.2$
-bash-4.2$ exit
logout
Connection to test-machine02 closed.
-bash-4.2$


Step 6.4. Configure Passwordless Authentication in PostgreSQL Database Server: Use OS command ssh-keygen to generate public and private keys. Once keys are generated use OS command ssh-copy-id to transfer the public key to Barman Server.

[root@test-machine02 ~]# su - postgres
Last login: Wed Jun 16 17:44:29 +03 2021 on pts/2
-bash-4.2$
-bash-4.2$
-bash-4.2$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/var/lib/pgsql/.ssh/id_rsa):
Created directory '/var/lib/pgsql/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /var/lib/pgsql/.ssh/id_rsa.
Your public key has been saved in /var/lib/pgsql/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:jiouqVEgyZz+dmsHM+H0yzn4GgdhYnqBkbJ3Es/ralw postgres@test-machine02
The key's randomart image is:
+---[RSA 2048]----+
| ..              |
|+o=              |
|=* B o           |
|+.= Bo.          |
| +.+ooo S        |
| .o E=.+         |
|.o = oB.+        |
|o.= o++*         |
|o+oooo+..        |
+----[SHA256]-----+
-bash-4.2$
 
-bash-4.2$ ls -ltr .ssh
total 8
-rw-r--r--. 1 postgres postgres  405 Jun 22 10:12 id_rsa.pub
-rw-------. 1 postgres postgres 1679 Jun 22 10:12 id_rsa
-bash-4.2$
 
-bash-4.2$ ssh-copy-id -i ~/.ssh/id_rsa.pub barman@test-machine01
/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/var/lib/pgsql/.ssh/id_rsa.pub"
/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
barman@test-machine01's password:
 
Number of key(s) added: 1
 
Now try logging into the machine, with:   "ssh 'barman@test-machine01'"
and check to make sure that only the key(s) you wanted were added.
 
-bash-4.2$
-bash-4.2$ ssh 'barman@test-machine01'
Last login: Tue Jun 22 10:32:10 2021
-bash-4.2$
-bash-4.2$ exit
logout
Connection to test-machine01 closed.
-bash-4.2$


Step 6.5. Configure WAL Shipping in PostgreSQL Database Server: Edit postgresql.conf and modify archive_command & archive_mode to copy WAL Files in barman server. As both are static parameter postgresql service needs to be restart.

[root@test-machine02 ~]# cd /var/lib/pgsql/13/data/
[root@test-machine02 data]# vi postgresql.conf
archive_mode = on
archive_command = 'barman-wal-archive test-machine01 test-machine02 %p'
:wq!

[root@test-machine02 system]# systemctl restart postgresql-13
[root@test-machine02 system]#

[root@test-machine02 ~]# su - postgres
Last login: Sun Jul 11 10:56:42 +03 2021 on pts/1
-bash-4.2$ psql
psql (13.2)
Type "help" for help.
postgres=#
postgres=# select name,setting,unit from pg_settings where name in ('archive_mode','wal_level','archive_command');
      name       |                       setting                       | unit
-----------------+-----------------------------------------------------+------
 archive_command | barman-wal-archive test-machine01 test-machine02 %p |
 archive_mode    | on                                                  |
 wal_level       | replica                                             |
(3 rows)

postgres=#


Step 6.6. Check barman-wal-archive working in Barman server: You can check that barman-wal-archive can connect to the Barman server, and that the required PostgreSQL server is configured in Barman to accept incoming WAL files with the following command:

-bash-4.2$
-bash-4.2$ barman-wal-archive --test test-machine01 test-machine02 DUMMY
barman@test-machine01's password:
Ready to accept WAL files for the server test-machine02
-bash-4.2$


Once the above steps are done continue from Step 7 to complete it following the blog How To Configure Streaming Backup & WAL Streaming using BARMAN.


References: BARMAN Document: http://docs.pgbarman.org/release/2.12/
For BARMAN Backup Command: https://dbsguru.com/physical-postgresql-backup-using-barman/
For BARMAN Restore Command: https://dbsguru.com/restore-backup-using-barman-in-postgresql/
For BARMAN PITR Comamnd:  https://dbsguru.com/point-in-time-recovery-using-barman-in-postgresql/

 

This document is just for learning purpose and always validate in the LAB environment first before applying in the LIVE environment.


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