PostgreSQL Cluster

Overview

PostgreSQL Cluster is a feature that enables deploying PostgreSQL with a 1 Writer (Primary) + N Readers (Replica) architecture, ensuring High Availability and the ability to scale read operations for production workloads on vDB.

What is PostgreSQL Cluster?

In the PostgreSQL Cluster model, nodes are assigned clear roles:

• Writer (Primary): The node that handles all write operations (INSERT, UPDATE, DELETE). Each cluster always has exactly 1 Writer.

• Reader (Replica): Read-only nodes that synchronize data from the Writer via Streaming Replication. A cluster can have from 1 to 9 Readers.

• Automatic Failover: When the Writer encounters an issue, a Reader is automatically promoted to Writer without manual intervention.

To create and manage a PostgreSQL Cluster, please refer to the guide here.

Single Node vs. Cluster Comparison

Feature	Single Node	Cluster
Architecture	1 single node	1 Writer + N Readers
High Availability	No	Yes (Automatic Failover)
Scale Read	No	Yes (Read traffic distributed to Readers)
Backup	Automatic daily backup (legacy)	Integrated with Backup Center (Auto Backup + Manual Backup)
Number of nodes	1	2 - 10
Use Case	Development, Testing, small applications	Production, Mission-critical, applications requiring high uptime

When should you use PostgreSQL Cluster?

• Production workloads: Applications requiring high uptime that cannot tolerate downtime.

• Read-heavy applications: Applications with heavy read traffic that need to scale out read operations.

• Mission-critical systems: Payment systems, transactions, and critical data that need protection by automatic failover.

• Data protection: Applications requiring a comprehensive backup strategy with Auto Backup and Manual Backup through Backup Center.

Note:

• Single Node is suitable for development and testing environments due to simpler configuration and lower cost.

• Cluster is recommended for production environments when High Availability and fault tolerance are required.

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PostgreSQL Cluster Architecture

Key components:

• Writer Node (Primary): Handles all write operations. Each cluster has exactly 1 Writer.

• Reader Node(s) (Replica): Handle read operations, synchronizing data from the Writer via Streaming Replication. Provide failover capability when the Writer encounters an issue.

• Automatic Failover: When the Writer node becomes unavailable, the system automatically promotes a Reader to become the new Writer, ensuring service continuity.

Role distribution by number of nodes:

Number of Nodes	Role Distribution
2	1 Writer + 1 Reader
3	1 Writer + 2 Readers
5	1 Writer + 4 Readers
10	1 Writer + 9 Readers

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Backup Center Integration

PostgreSQL Cluster is integrated with Backup Center (vBackup), providing a comprehensive backup & restore solution:

• Auto Backup: Mandatory configuration when creating a cluster. Backup runs automatically according to the schedule of the selected Backup Policy.

• Manual Backup: Allows creating a Full Snapshot manually at any time from the cluster detail page.

• Restore: Create a new cluster from an available restore point in Backup Center. The Storage Size of the new cluster must be greater than or equal to the Backup Size.

Note about Backup when deleting a Cluster:

• Auto Backup: Will be automatically deleted when the cluster is deleted.

• Manual Backup: Will be retained after the cluster is deleted. You need to manually manage and delete it in Backup Center if no longer needed.

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Limitations and Notes

Current Limitations

Limitation	Description
Number of nodes	Minimum 2, maximum 10 nodes per cluster
Writer node	Always exactly 1 Writer per cluster
Database Proxy	Not supported in current version (Coming Soon - Phase 2)
Concurrent backups	Only 1 backup/restore job allowed at a time per cluster

Important Notes

About Reserved Usernames:

When creating a cluster, you must not use the following usernames as the Master Username as they are reserved by the system: postgres, admin, cron_admin, robot_zmon, vngpooler, vngpam, vngrep, vngsuperrole.

About Deployment Type:

The PostgreSQL Cluster feature is only available when selecting PostgreSQL as the Engine. Other engines (MySQL, MariaDB) currently only support the Single Node deployment type.

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FAQ

1. Can I switch from Single Node to Cluster?

No. vDB currently does not support changing the Deployment Type after a database has been created. You need to create a new cluster and migrate the data.

2. What happens when the Writer node encounters an issue?

When the Writer node encounters an issue, the system will automatically failover: a Reader node will be promoted to become the new Writer. This process happens automatically without manual intervention. The UI will update the role of the nodes after the failover is complete.

3. Can I create a cluster from an existing backup?

Yes. When creating a new cluster, you can select a restore point from Backup Center to restore data. Note that the Storage Size of the new cluster must be greater than or equal to the Backup Size of the backup.

4. What is Database Proxy and when will it be available?

Database Proxy provides connection pooling and load balancing for the cluster. This feature is under development and will be released in Phase 2. Please follow the Announcements and Updates page for the latest information.