The configurations are saved in the file located at the root of data folder (e.g /var/lib/pgsql/12/data/) and read addition to those stored in nf. The ALTER SYSTEM SET SQL command is a powerful feature to change a server’s configuration parameters, directly with a SQL query. $ psql -c "ALTER SYSTEM SET listen_addresses TO '*' " On the master server, switch to the postgres system account and configure the IP address(es) on which the master server will listen to for connections from clients. Step 1: Configuring the PostgreSQL Master/Primary Database Serverġ. Note: PostgreSQL 12 comes with major changes to replication implementation and configuration such as replacement of nf and the conversion of nf parameters to normal PostgreSQL configuration parameters, making it much easier to configure cluster replication. Postgresql standby database server: 10.20.20.8īoth database servers must have Postgresql 12 installed, otherwise, see: How to Install PostgreSQL and pgAdmin in CentOS 8. This guide assumes you connected to your master and standby database servers as the root via SSH (use Sudo command where necessary if you are connected as a normal user with administrative rights): Postgresql master database server: 10.20.20.9 Note that compared to other methods, replication slots retain only the number of segments known to be needed.
We will use “ replication slots” for the standby as a solution to avoid the master server from recycling old WAL segments before the standby has received them. This guide shows how to set up a Postgresql 12 master-standby streaming replication on CentOS 8. One downside of this approach is that in case the master server crashes, any uncommitted transactions may not be replicated and this can cause data loss. This means that there is a small delay between committing a transaction in the master server and the changes becoming visible in the standby server. With streaming replication, a standby (replication slave) database server is configured to connect to the master/primary server, which streams WAL records to the standby as they are generated, without waiting for the WAL file to be filled.īy default, streaming replication is asynchronous where data is written to the standby server(s) after a transaction has been committed on the primary server. This solution allows for a standby server to be implemented using file-based log shipping or streaming replication, or where possible, a combination of both approaches. In the next article, I discuss how to Backup and restore PostgreSQL databases with Ansible using a database dump.PostgreSQL database supports several replication solutions to build high-availability, scalable, fault-tolerant applications, one of which is Write-Ahead Log ( WAL) Shipping. We have seen how to install and configure a PostgreSQL database with a database user, and how to run an initial SQL migration (or any other SQL script). Service : name=postgresql state=restarted name : "Find out if PostgreSQL is initialized"
Let's now create the Ansible playbook! First, we need to install the database itself, along with psycopg2-binary Python library that will allow us to use Ansible PostgreSQL modules postgresql_db, postgresql_user, postgresql_privs and postgresql_pg_hba.
Just create ansible.cfg and hosts.ini files with the proper connection information, or modify the playbook itself. The playbook expects that we configure the target machines using an inventory file. When needed, use Ansible Vault or environment variables when running the playbook. Note that storing passwords in plain text is not the best idea.
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