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Building the Primary/Secondary PostgreSQL Architecture

Last updated: 2020-08-10 10:59:54

Overview

PostgreSQL is an open source relational database management system emphasizing scalability and standard compliance. PostgreSQL is ideal for enterprise-level complex online transaction processing (OLTP) systems. It supports NoSQL (JSON/XML/hstore) and Geographic Information System (GIS) data types. Featuring strong reliability and data integrity, PostgreSQL is a suitable for websites, location application systems, complex data object processing and other use cases.

This document describes how to build a PostgreSQL system on a CVM instance running CentOS 7.

Software

This document uses the following software as an example to build PostgreSQL.
Linux: Linux operating system. This document uses CentOS 7.6 as an example.
PostgreSQL: Relational database management system. This document uses PostgreSQL 11.2 as an example.

Prerequisites

Two created CVM instances. One CVM instance works as the primary node and the other works as the secondary node.
For more information, see Creating Instances via CVM Purchase Page.
The security group rules for the two CVM instances have already been configured. Open the port 5432.
For more information, see Adding Security Group Rules.

Directions

Configuring primary node

Log in to the primary CVM instance.
Run the following command to upgrade all packages, system versions and kernels.
```
yum update -y
```

Run the following command to install PostgreSQL storage repository.

yum install https://download.postgresql.org/pub/repos/yum/reporpms/EL-6-x86_64/pgdg-redhat-repo-latest.noarch.rpm

Run the following command to install client package.
```
yum install postgresql11
```
Run the following command to install server package.
```
yum install postgresql11-server
```
Run the following command to initialize the database.
```
/usr/pgsql-11/bin/postgresql-11-setup initdb
```
Run the following command to start the service.
```
systemctl start postgresql-11
```
Run the following command to enable service autostart.
```
systemctl enable postgresql-11
```
Run the following command to switch to the postgres user.
```
su - postgres
```
Run the following command to enter the PostgreSQL terminal.
```
psql
```
Run the following command to set password for the postgres user.
```
ALTER USER postgres WITH PASSWORD 'Custom password';
```
Run the following command to create a database account (such as postuser) and set the password, login permission and backup permission.
```
create role account name login replication encrypted password 'Custom password';
```
For example, use the following command to create a database account naming postuser with the password postuser:
```
create role postuser login replication encrypted password 'postuser';
```
Run the following command to check if the account has been created.
```
SELECT usename from pg_user;
```
If the following result is returned, it indicates that the account has been successfully created.
```
usename  
----------
postgres
postuser
(2 rows)
```
Run the following command to check if the permission has been set.
```
SELECT rolname from pg_roles;
```
If the following result is returned, it indicates that the permission has been successfully set.
```
rolname  
----------
postgres
postuser
(2 rows)
```
Enter \q and press Enter to exit the PostgreSQL terminal.
Enter exit and press Enter to exit PostgreSQL.
Run the following command to open the pg_hba.conf file.
```
vim /var/lib/pgsql/11/data/pg_hba.conf
```

Press i to switch to edit mode. Add the following two lines to IPv4 local connections.

host    all             all             <IPv4 IP range of the secondary node’s VPC>          md5     #Enable the MD5 password encryption for connections in the IP ranges of the VPC
host    replication     database account        <IPv4 IP range of the secondary node’s VPC>        md5     ##Allow data synchronization from the `replication` database.

For example, if the database account is postuser and the IPv4 IP range of the secondary node’s VPC is 192.10.0.0/16, add the following content to IPv4 local connections:

host    all             all             192.10.0.0/16          md5
host    replication     postuser        192.10.0.0/16          md5

Press Esc and enter :wq to save the file.
Run the following command to open the postgresql.conf file.
```
vim /var/lib/pgsql/11/data/postgresql.conf
```

Press i to enter edit mode, locate and modify the following parameters.

listen_addresses = 'xxx.xxx.xxx.xxx'   #The private IP addresses that are listened on.
max_connections = 100    #The maximum connections. The value of `max_connections` for the secondary node must be greater than that for the primary node
wal_level = hot_standby  #Enable hot standby mode.
synchronous_commit = on  #Enable synchronous replication
max_wal_senders = 32     #The maximum number of synchronization processes
wal_sender_timeout = 60s ##The timeout value for the streaming replication instance to send data.

Press Esc and enter :wq to save and close the file.
Run the following command to restart the service.
```
systemctl restart postgresql-11
```

Configuring secondary node

Log in to the secondary CVM instance.
Run the following command to upgrade all packages, system versions and kernels.
```
yum update -y
```

Run the following command to install PostgreSQL storage repository.

yum install https://download.postgresql.org/pub/repos/yum/reporpms/EL-6-x86_64/pgdg-redhat-repo-latest.noarch.rpm

Run the following command to install client package.
```
yum install postgresql11
```
Run the following command to install server package.
```
yum install postgresql11-server
```
Run the following command and use the pg_basebackup utility to create a backup directory:
```
pg_basebackup -D /var/lib/pgsql/11/data -h Private IP of primary node -p 5432 -U Database account -X stream -P
```
For example, if the private IP of the primary node is 192.10.123.321, and the database account is postuser, run the following command:
```
pg_basebackup -D /var/lib/pgsql/11/data -h 192.10.123.321 -p 5432 -U postuser -X stream -P
```
Enter the password as prompted, and press Enter. If the following is returned, it indicates that the backup directory has been successfully created.
```
Password: 
24526/24526 kB (100%), 1/1 tablespace
```

Run the following command to copy configuration files of the primary node.

cp /usr/pgsql-11/share/recovery.conf.sample /var/lib/pgsql/11/data/recovery.conf

Run the following command to open the recovery.conf file.
```
vim /var/lib/pgsql/11/data/recovery.conf
```

Press i to switch to edit mode, locate and modify the following parameters:

standby_mode = on     #Declare the secondary node
primary_conninfo = ‘host=<Private IP of the primary node> port=5432 user=Database account password=Database password’ #Connection information of the primary node
recovery_target_timeline = ‘latest’ #Synchronize the latest data by using streaming replication

Press Esc and enter :wq to save the file.
Run the following command to open the postgresql.conf file.
```
vim /var/lib/pgsql/11/data/postgresql.conf
```

Press i to switch to edit mode, locate and modify the following parameters:

listen_addresses= 'xxx.xx.xx.xx'   #The private IP addresses that are listened on.
max_connections = 1000             #The maximum connections. The value of `max_connections` for the secondary node must be greater than that for the primary node
hot_standby = on                   #Enable hot standby mode
max_standby_streaming_delay = 30s  #The maximum delay for streaming replication
wal_receiver_status_interval = 1s  #The maximum interval for the secondary node to report its status to the primary node
hot_standby_feedback = on          #Enable the secondary node to report errors during replication.

Press Esc and enter :wq to save the file.
Run the following command to modify the group and owner of data directory:
```
chown -R postgres.postgres /var/lib/pgsql/11/data
```
Run the following command to start service.
```
systemctl start postgresql-11
```
Run the following command to enable service autostart.
```
systemctl enable postgresql-11
```

Verifying deployment

Perform the following to verify the deployment.

Run the following command to check the sender process on the primary node:
```
ps aux |grep receiver
```
If the following is returned, it indicates that the sender process is available.
Run the following command to check the receiver process on the secondary node:
```
ps aux | grep receiver
```
If the following is returned, it indicates that the receiver process is available.
On the primary node, run the following commands in sequence to check the secondary node status in the PostgreSQL terminal.
```
su - postgres
```
```
psql
```
```
select * from pg_stat_replication;
```
If the following is returned, it indicates that the secondary node status is available.
Verify that the secondary node synchronizes data with the primary node.
1. On the primary node, run the following command to enter PostgreSQL terminal and create a database (such as testdb).
```
su - postgres
```
```
psql
```
```
create database testdb;
```
2. On the secondary node, run the following commands in sequence to enter PostgreSQL terminal and check whether the secondary node is synchronized.
```
su - postgres
```
```
psql
```
```
"l",
```
  If the following is returned, it indicates that the secondary node has been successfully synchronized.