Tair (Redis OSS-compatible) is a high-performance key-value database service. This service helps you store large amounts of important data in various scenarios. This topic describes the disaster recovery solutions provided by Tair.
Evolution of Tair disaster recovery solutions
A Tair instance may fail for unexpected reasons, such as a device failure or a power failure in a data center. In this case, disaster recovery can help ensure data consistency and service availability.
Figure 1. Evolution of Tair disaster recovery solutions
Disaster recovery solution | Protection level | Description |
★★★☆☆ | The master node and the replica node are deployed on different machines in the same zone. If the master node fails, the high availability (HA) system performs a failover to prevent service interruption caused by a single point of failure (SPOF). | |
★★★★☆ | The master node and the replica node are deployed in two different zones of the same region. If the zone in which the master node resides is disconnected due to force majeure factors such as a power or network failure, the HA system performs a failover to ensure continuous availability of the entire instance. | |
★★★★★ | In the architecture of Global Distributed Cache, a distributed instance consists of multiple child instances that synchronize data among each other in real time by using synchronization channels. The channel manager monitors the health status of child instances and handles exceptions that occur on child instances, such as a switchover between the primary and secondary databases. Global Distributed Cache is suitable for scenarios such as geo-disaster recovery, active geo-redundancy, nearby application access, and load balancing. |
Single-zone HA solution
All Tair instances support the single-zone HA architecture. The HA system monitors the health status of the master and replica nodes and performs failovers to prevent service interruption caused by SPOFs.
Deployment architecture | Description |
Figure 2. HA architecture for a standard master-replica instance A standard master-replica instance runs in a master-replica architecture. If the HA system detects a failure on the master node, the system switches the workloads from the master node to the replica node and the replica node takes over the role of the master node. The original master node works as the replica node after recovery. | |
Figure 3. HA architecture for a cluster master-replica instance In a cluster master-replica instance, data is stored on data shards. Each data shard consists of a master node and a replica node. The master node and the replica node are deployed on different machines in an HA architecture. If the master node fails, the HA system performs a master-replica switchover to ensure high service availability. For more information about the components of a cluster instance, see Cluster master-replica instances. | |
Figure 4. HA architecture for a read/write splitting instance
For more information about the components of a read/write splitting instance, see Read/write splitting instances. |
Zone-disaster recovery solution
Tair standard instances and cluster instances support zone-disaster recovery across two data centers. If your workloads are deployed in a single region and require disaster recovery, you can select the zones that support zone-disaster recovery when you create a Tair instance. For more information about how to create a Tair instance, see Step 1: Create an instance.
Figure 5. Create a zone-disaster recovery instance 
After you create a zone-disaster recovery instance, a replica node that has the same specifications as the master node is deployed in a different zone than the master node. The master node synchronizes data to the replica node over a dedicated channel.
If a power failure or a network error occurs on the master node, the replica node takes over the role of the master node. The system calls an API operation on the configuration server to update routing information for proxy nodes. In addition, Tair provides an optimized Redis synchronization mechanism. Similar to global transaction identifiers (GTIDs) of MySQL, Tair uses global operation identifiers (OpIDs) to indicate synchronization offsets and runs lock-free threads in the background to search for OpIDs. The system asynchronously synchronizes append-only file (AOF) binary logs (binlogs) from the master node to the replica node. You can throttle synchronization to ensure service performance.
Cross-region disaster recovery solution
If your business rapidly grows and branches out into a wide range of regions, cross-region and long-distance access can result in high latency and deteriorate user experience. The Global Distributed Cache feature of Alibaba Cloud Tair can help you reduce the high latency caused by cross-region access. The Global Distributed Cache feature has the following benefits:
Allows you to directly create child instances or specify the child instances that need to be synchronized without having to build redundancy into your application. This greatly reduces the complexity of application design and allows you to focus on application development.
Provides the geo-replication capability to implement geo-disaster recovery or active geo-redundancy.
This feature applies to cross-region data synchronization scenarios and global business deployment in industries such as multimedia, gaming, and e-commerce. For more information, see Overview of Global Distributed Cache for Tair.
Figure 7. Architecture of Global Distributed Cache for Tair 