Product Series

RDS for PostgreSQL DB instances are classified into the following types:

**Table 1** DB instance types
DB Instance Type	Description	Notes	Scenarios
Single-node	A single-node architecture is more cost-effective than a primary/standby DB pair.	If a fault occurs on a single-node instance, the instance cannot recover in a timely manner.	Personal learning Microsites Development and testing environment of small- and medium-sized enterprises
Primary/Standby	An HA architecture. A pair of primary and standby DB instances shares the same IP address and can be deployed in different AZs.	When a primary instance is being created, a standby instance is provisioned along with it to provide data redundancy. The standby instance is invisible to you after being created. If the primary instance fails, a failover occurs, during which database connection is interrupted. If there is a replication delay between the primary and standby instances, the failover takes an extended period of time. The client needs to be able to reconnect to the instance.	Production databases of large and medium enterprises Applications for the Internet, Internet of Things (IoT), retail e-commerce sales, logistics, gaming, and other industries

Single-node DB instances: support the creation of read replicas and support the queries of error logs and slow query logs. Different from a primary/standby DB instance that has two database nodes, a single-node DB instance has only one node, reducing the price to half of a primary/standby DB instance. If the node fails, the restoration will take a long time. Therefore, single-node DB instances are not recommended for workloads that are highly sensitive to database availability.
Primary/Standby DB instances: use the standby database node only for failover and restoration. The standby database node does not provide services. The performance of single-node DB instances is similar to or even higher than primary/standby DB instances because standby nodes cause extra performance overhead.

**Table 2** Function comparisons
Function	Single-Node	Primary/Standby
Number of nodes	1	2
Specifications	vCPUs: a maximum of 64 Memory: a maximum of 512 GB Storage: a maximum of 4,000 GB	vCPUs: a maximum of 64 Memory: a maximum of 512 GB Storage: a maximum of 4,000 GB
Monitoring and alarms	Supported	Supported
Security group	Supported	Supported
Backup and restoration	Supported	Supported
Recycle bin	Supported	Supported
Parameter settings	Supported	Supported
SSL	Supported	Supported
Log management	Supported	Supported
Read replicas (which need to be created)	Supported	Supported
High-frequency monitoring	Supported	Supported
Failover	Not supported	Supported
Standby DB instance migration	Not supported	Supported
Manual primary/standby switchover	Not supported	Supported
Instance class change	Supported	Supported