A three-zone PolarDB-X instance distributes nodes across three availability zones in the same region. Master compute nodes in the primary zone handle all read and write operations. Standby compute nodes in the secondary zones remain on standby for failover. This document explains how to change the primary zone and how to move leader data nodes back to the primary zone when they drift after a failover.
How it works
In a three-zone instance:
Master compute nodes (primary zone): process all database read and write operations and maintain the most up-to-date data state.
Standby compute nodes (secondary zones): stay in standby mode and are ready to quickly take over the workload of master nodes if the primary zone fails.
Leader data nodes: manage data shards. For optimal performance, all leader data nodes should reside in the primary zone.
View zone information
After purchasing a three-zone instance, check zone distribution in the following locations:
Instances page: shows the primary zone and secondary zone for each three-zone instance.
Basic Information page: displays the primary zone and secondary zone of the instance.
Topology Information section (on the Basic Information page): shows the zone and status of each individual node.
Create a three-zone instance
When purchasing a PolarDB-X instance, set the Topology parameter to Three-zone or Single-zone. To create a three-zone instance, set the Topology parameter to Three-zone. For details, see Create a PolarDB-X instance.
Change the primary zone
Changing the primary zone causes transient connections. Schedule this operation during off-peak hours.
Log on to the PolarDB for Xscale console.
In the top navigation bar, select the region where your instance is located.
On the Instances page, click the PolarDB-X 2.0 tab.
Click the instance ID.
In the left-side navigation pane, click Basic Information. In the Topology Information section, click Specify Primary Zone.
In the Specify Primary Zone dialog box, select the zone ID and click OK.
The instance status changes to Under HA Switchover. When the status returns to Running, the primary zone change is complete.
FAQ
What are standby compute nodes used for?
Standby compute nodes in the secondary zones act as hot backups for the master compute nodes in the primary zone. They serve backups and are ready to quickly take over the workload of master nodes in the event of a failure of the primary zone — at which point their role changes from standby to master.
To trigger a role switch manually (for example, to restore expected zone roles after a failover), go to Basic Information > Topology Information, click Specify Primary Zone, select the current primary zone ID, and click OK.
Some leader data nodes are not in the primary zone. How do I fix this?
Go to Basic Information > Topology Information, click Specify Primary Zone, select the primary zone ID from the Primary Zone drop-down list, and click OK.