Create a Multi-AZ PostgreSQL Cluster
This guide shows you how to create a PostgreSQL Cluster whose Nodes are spread across multiple Availability Zones in the Ho Chi Minh region, so the cluster keeps serving traffic when one Availability Zone fails.
What is Multi-AZ
A PostgreSQL Cluster on vDB has two deployment modes, selected in the Availability & Durability field:
Single-AZ — every Node sits in one Availability Zone.
Multi-AZ — Nodes are spread across two or more Availability Zones. When one Availability Zone becomes unreachable, a Replica in a remaining Availability Zone is promoted to Primary and the cluster keeps running.
HCM03-1A HCM03-1B
┌──────────────────┐ ┌──────────────────┐
│ Primary (Writer) │ ─────────────→ │ Replica (Reader) │
│ Read / Write │ Streaming │ Read / Failover │
└──────────────────┘ Replication └──────────────────┘Node placement
All Nodes in one Availability Zone
Nodes spread across two or more Availability Zones
Availability Zone fault tolerance
No
Yes
Where zones are selected
The Basic configuration step
The Network & Security step, together with the Subnet
VPC requirement
None
The VPC must have DNS enabled
Available regions
HCM, HAN
HCM only
Subnets to select
1
One Subnet per zone — at least 2 zones, so at least 2 Subnets
Prerequisites
A GreenNode account with access to the vDB service.
You are working in the HCM region — Multi-AZ is currently available in Ho Chi Minh only.
A VPC in HCM that has DNS enabled.
That VPC has Subnets in at least two different Availability Zones.
A Backup Policy and a Backup Location in the Available status on Backup Center — Backup Settings are mandatory for every PostgreSQL Cluster.
Create a Multi-AZ Cluster
Step 1: Select the Multi-AZ mode
Go to vDB Relational at https://vdb.console.greennode.ai/relational/database, or from the GreenNode homepage open the vServer service and select vDB Relational.
Select HCM in the Region selector in the top navigation bar.
Click Create Database.
In Basic configuration, select PostgreSQL as the ENGINE.
Select PostgreSQL Cluster as the Deployment type.
Enter the CLUSTER NAME: 6–20 characters, starting with an alphabetic character, using
a-z,A-Z,0-9,_,-,.,@and spaces. Leave it empty and the system generates a name for the cluster.Open the Availability & Durability dropdown and select Multi-AZ.
Once Multi-AZ is selected, the Zone group no longer appears in Basic configuration. In Multi-AZ mode you select zones in Step 3, together with the Subnet, because each zone must be paired with exactly one Subnet of the VPC you choose.
Changing Availability & Durability clears every zone and Subnet you have selected, in both directions and at any point — including after you have finished filling in Network & Security. Select the mode before configuring the network.
Step 2: Choose the number of Nodes
In Cluster specification, select the Engine license and the Engine version.
Enter Number of nodes: at least 2, at most 10.
Check the role distribution shown next to the field.
2
1 Primary (Writer) · 1 Replica (Reader)
3
1 Primary (Writer) · 2 Replicas (Reader)
5
1 Primary (Writer) · 4 Replicas (Reader)
10
1 Primary (Writer) · 9 Replicas (Reader)
Step 3: Select the VPC and one Subnet per zone
Scroll to Network & Security.
Select the VPC for this cluster. The dropdown only shows VPCs that have DNS enabled; if no suitable VPC exists, use the VPC management link below the field.
In the Subnets table, tick the zones you want to deploy to. The first two zones in the list are ticked by default — in the HCM region these are HCM03-1A and HCM03-1B.
For each ticked zone, select a Subnet in the right-hand column.
Enable Public accessibility if you want to reach the cluster from the Internet.
Minimum zones
You must tick at least two different zones
Subnet per zone
Each ticked zone must have exactly one Subnet selected
Same VPC
Every Subnet must belong to the VPC you selected
Zone with no Subnet
A zone with no Subnet in the VPC is disabled in the table
Zone without the Storage type
A zone that does not support the Storage type you selected in Cluster specification cannot be used either. A warning appears on the Subnets table, for example Zone HCM 1C: NVMe storage type not supported
Public accessibility can only be set once, at creation time, and cannot be changed afterwards.
Step 4: Complete the remaining steps
The remaining sections of the creation flow are the same as for Single-AZ:
Cluster specification — Instance family, CPU Platform, Package (Core, Ram, Free backup), Storage type, Storage size.
DB instance settings — Master username and Master password. Note that the Master username must not match any of the reserved system usernames.
Database options — Database name and Configuration group (optional).
Backup settings — Backup Policy and Backup Location, mandatory for every PostgreSQL Cluster.
For each field in detail, see Create and Manage PostgreSQL Cluster.
Review the Summary panel on the right, then click CREATE DATABASE.
Result
The cluster enters the Building status, then moves to Active once provisioning completes. Open the cluster detail page to verify:
The General information section shows Availability & Durability as Multi-AZ, along with the engine version and the Node count of the cluster.
The Connectivity & Security tab shows a Select zone tab group, one tab per Availability Zone of the cluster.
Connect to a Multi-AZ Cluster
In the Connectivity & Security tab, each zone tab shows two endpoint groups:
PRIMARY ENDPOINT (READ/WRITE)
Read and write queries, pointing at the Primary Node
READER ENDPOINT (READ-ONLY, LOAD BALANCED)
Read-only queries, load balanced across the Replica Nodes
Each group contains a Private Endpoint, a Public Endpoint and a Domain Endpoint, each with a copy control. Take the Port shown in the endpoint group you are using.
GreenNode recommends using the Domain Endpoint in your application connection string:
The Domain Endpoint is a single value for the whole cluster and does not change when you switch to another zone tab.
The Domain Endpoint does not change on failover, so your application does not need reconfiguring each time the Primary moves to another Node.
You can check the addresses the Domain Endpoint resolves to with:
Use the per-zone Private Endpoint and Public Endpoint addresses when you need a specific address, for example to open a firewall rule or to configure routing.
For client tools, connection strings and the sslmode=require parameter, see Connect to an RDS Instance.
Limitations and notes
Region
HCM only. The HAN region offers PostgreSQL Cluster but does not support Multi-AZ yet
Number of Nodes
At least 2, at most 10
Availability Zones
At least 2
VPC
Must have DNS enabled
Changing the mode after creation
Switching between Single-AZ and Multi-AZ after the cluster is created is not supported. Create a new cluster instead
Configuration group
A Configuration group is bound to a deployment type; a group created for Cluster cannot be applied to a Single Node, and vice versa
Storage when restoring from a backup
The new cluster needs more storage than the backup itself. The system shows the required minimum on the Storage size field once you select a backup — enter that value or higher
See also
Understand the PostgreSQL Cluster architecture and concepts
Manage the cluster: backup, resize, change the Node count
Connect to the database with a client tool
Configure parameters for the cluster
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