This page is an overview of the high availability (HA) configuration for Cloud SQL instances. To configure a new instance for HA, or to enable HA on an existing instance, see Enabling and disabling high availability on an instance.
HA configuration overviewThe purpose of an HA configuration is to reduce downtime when a zone or instance becomes unavailable. This might happen during a zonal outage, or when there's a hardware issue. With HA, your data continues to be available to client applications.
The HA configuration provides data redundancy. A Cloud SQL instance configured for HA is also called a regional instance and has a primary and secondary zone within the configured region*. Within a regional instance, the configuration is made up of a primary instance and a standby instance. Through synchronous replication to each zone's persistent disk, all writes made to the primary instance are replicated to disks in both zones before a transaction is reported as committed. In the event of an instance or zone failure, the standby instance becomes the new primary instance. Users are then rerouted to the new primary instance. This process is called a failover.
Note: There are cases where Cloud SQL issues a restart instead of a failover. When this happens, you see Restart as an operation on the instance when you view the Operations and logs pane on the instance Overview page or on the instance Operations page. For example, the database can restart when a resource is exhausted, such as when an instance runs out of memory. To avoid downtime due to memory issues, see Optimize high memory consumption.After a failover, the instance that received the failover continues to be the primary instance, even after the original instance comes back online. After the zone or instance that experienced an outage becomes available again, the original primary instance is destroyed and recreated. Then it becomes the new standby instance. If a failover occurs in the future, the new primary will fail over to the original instance in the original zone.
If you need to have the primary instance in the zone that had the outage, you can do a failback. A failback performs the same steps as the failover, only in the opposite direction, to reroute traffic back to the original instance. To perform a failback, use the procedure in Initiating failover.
Regional persistent disk support for Cloud SQL HA configuration that has at least one dedicated CPU has full Service Level Agreement (SLA) coverage. An HA-configured instance costs twice as much as a standalone instance. This price includes CPU, RAM, and storage. For more information, see the pricing page.
* For more information about region-specific considerations, see Geography and regions.
You can create an account to evaluate how Cloud SQL performs in real-world scenarios. New customers also get $300 in free credits to spend on Cloud SQL to run, test, and deploy workloads. You won't be charged until you upgrade.
Sign up to try Cloud SQL for free.
Read replicasIf availability is a consideration for your read replicas, you can enable HA on the replicas. When you promote such a replica to become a primary instance, it's already set up as a highly available instance.
During a zonal outage, traffic stops to read replicas in that zone. After the zone becomes available again, any read replicas in the zone resume replication from the primary instance. If read replicas are not located in a zone that is undergoing an outage, they connect to the standby instance when it becomes the primary instance.
As a best practice, consider putting some of your read replicas in a different zone from the primary and standby instances. For example, if you have a primary instance in zone A and a standby instance in zone B, put a read replica in zone C to improve your reliability. This practice ensures that read replicas continue to operate even if the zone for the primary instance goes down. You should also add business logic in the client application to send reads to the primary instance when read replicas are unavailable.
Failover overviewIf an HA-configured instance becomes unresponsive, Cloud SQL automatically switches to serving data from the standby instance. To see if a failover has occurred, check your operation log failover history.
Learn more about how to build queries in the Logs Explorer. If you need more detailed information about an operation, such as the user who performed the operation, you must enable audit logging.
Click the tabs to see how failover affects your instance.
Normal Failover Post-Failover Failback ProcessThe following process occurs:
The primary instance or zone fails.
Each second, the heartbeat system detects whether the primary instance is healthy. If multiple heartbeats aren't detected, failover is initiated.
The standby instance now serves data upon reconnection.
Through a shared static IP address with the primary instance, the standby instance now serves data from the secondary zone.
For Cloud SQL to allow a failover, the configuration must meet the following requirements:
Automated backups are highly recommended for high availability.
Recovery options for standalone instancesCloud SQL doesn't recover standalone instances from a zonal outage automatically. To re-establish an instance that isn't configured for high availability to a healthy zone, you must restore any zonal instances manually. You can recover a standalone instance from a zonal outage manually by using one of the following options:
Perform point-in-time recovery on the instance to a new instance that you create. To use this option, you must have enabled PITR on the zonal instance prior to the zonal outage. The transaction logs for the instance must be stored in Cloud Storage. If the transaction logs are stored on disk, then you can switch them to Cloud Storage. To use this option, follow the steps in Perform PITR on an unavailable instance.
If the instance has a read replica in a different zone, then you can promote that read replica to replace the standalone instance that's experiencing the zonal outage. To use this option, follow the steps in Promote a replica
For both options, the following considerations apply:
Some recent transactions committed on the primary instance might not appear on the newly recovered instance. The interval of time where transactions might have been lost is the recovery point objective (RPO).
After you perform either of the restoration options, you must reconfigure any clients of the instances that experience the zonal outage because the recovered instances will have different IP addresses and connection names.
There is no difference in working with non-HA and HA instances, so your application does not need to be configured in any particular way. When failover occurs, any existing connections to the primary instance and read replicas are closed, and it will take approximately 60 seconds for connections to the primary instance to be reestablished. Your application reconnects using the same connection string or IP address, so you do not need to update your application after failover.
To see exactly how your applications are affected by failover, manually initiate failover.
Maintenance downtimeMaintenance events affect primary instances configured with HA in the same way as other instances. You can expect primary instances to be down for a brief period of time. For more information on how maintenance affects HA instances, see How maintenance works. To minimize impact to your service, change maintenance settings to control when downtime occurs.
What's nextRetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4