Ubuntu 20.04
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PostgreSQL 12 : Streaming Replication
2020/09/01
 
Configure PostgreSQL Streaming Replication.
This configuration is common Primary/Replica settings.
[1]
[2] Configure Primary Node.
root@dlp:~#
vi /etc/postgresql/12/main/postgresql.conf
# line 59: uncomment and change

listen_addresses = '
*
'
# line 192: uncomment

wal_level = replica
# line 197: uncomment

synchronous_commit = on
# line 285: uncomment (max number of concurrent connections from streaming clients)

max_wal_senders = 10
# line 287: uncomment and change (minimum number of past log file segments)

wal_keep_segments =
10
# line 300: uncomment and change

synchronous_standby_names = '
*
'
root@dlp:~#
vi /etc/postgresql/12/main/pg_hba.conf
# add to the end

# host replication [replication user] [allowed network] [authentication method]

host    replication     rep_user        10.0.0.30/32            md5
host    replication     rep_user        10.0.0.51/32            md5

# create a user for replication

root@dlp:~#
su - postgres

postgres@dlp:~$
createuser --replication -P rep_user

Enter password for new role:  
# set any password

Enter it again:
postgres@dlp:~$
exit
root@dlp:~#
systemctl restart postgresql
[3] Configure Replica Node.
# stop PostgreSQL and remove existing data

root@node01:~#
systemctl stop postgresql

root@node01:~#
rm -rf /var/lib/postgresql/12/main/*
# get backup from Primary Node

root@node01:~#
su - postgres

postgres@node01:~$
pg_basebackup -R -h dlp.srv.world -U rep_user -D /var/lib/postgresql/12/main -P

Password:  
# password of replication user

32540/32540 kB (100%), 1/1 tablespace
postgres@node01:~$
exit
root@node01:~#
vi /etc/postgresql/12/main/postgresql.conf
# line 59: uncomment and change

listen_addresses = '
*
'
# line 315: uncomment

hot_standby = on
root@node01:~#
vi /var/lib/postgresql/12/main/postgresql.auto.conf
# add [application_name] to auto generated auth file (any name you like, like hostname and so on)

primary_conninfo = 'user=rep_user password=p0pswd07 host=www.srv.world port=5432 sslmode=prefer sslcompression=0 gssencmode=prefer krbsrvname=postgres target_session_attrs=any application_name=node01'

root@node01:~#
systemctl start postgresql

[4] That's OK if result of the command below on Primary Node is like follows. Make sure the setting works normally to create databases or to insert data on Primary Node.
postgres@dlp:~$
psql -c "select usename, application_name, client_addr, state, sync_priority, sync_state from pg_stat_replication;"

 usename  | application_name | client_addr |   state   | sync_priority | sync_state
----------+------------------+-------------+-----------+---------------+------------
 rep_user | node01           | 10.0.0.51   | streaming |             1 | sync
(1 row)
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