When you need a database disaster recovery solution based on cloud services deployed in the same city, you can purchase an Alibaba Cloud DTS instance for data migration and real-time synchronization. The disaster recovery solution supports three modes: Replication and high availability, active/standby (A-S), and active-active (A-A).
  • Replication and high availability: One database is deployed in each of the two data centers. You can copy data from the database of the primary data center to that of the secondary data center. If a fault occurs on the database of the primary data center, business switches to the database of the secondary data center.
  • Active/standby mode: Both data centers are deployed with the same system. The secondary data center is used only to back up data. If a fault occurs on the primary data center, business switches to the secondary data center.
  • Active/active mode: Both data centers are deployed with the same system, each with independent workloads and hosted services. Both data centers reserve some of their respective resources for data backup. If a fault occurs on either of the data centers, business switches to the other data center and the reserved resources are used. We recommend that you use the active/standby mode, if you have sufficient resources and have demanding requirements for zone-disaster recovery. If your resources are limited, we recommend that you use the active/active mode.

Replication and high availability

Relational Database Service (RDS) is used as an example to introduce the architecture of the replication and high availability mode.

Architecture:
  • Key conditions:
    • RDS clusters are deployed in data centers A and B, respectively.
    • SLB, ECS, and HA systems can be connected to applications across data centers. You only need to deploy one set of SLS, ECS, and HA systems in data centers A and B. You can manage and control the databases in the two data centers by using the HA system.
  • Data backup and recovery:
    • This mode copies the data from the databases in Data Center A to the databases in Data Center B.
    • If a fault occurs on the databases in Data Center A, the HA system directs traffic to Data Center B. The resources of Data Center A remain unavailable if the fault persists. After Data Center A is recovered, you can specify it as a secondary zone.
  • Features:
    • Advantages: lightweight switchover and low costs.
    • Disadvantages: risks of data inconsistency. A small amount of data may be inconsistent after the switchover, such as the loss of a transaction.

Active/standby mode

An example is used to introduce the architecture of the active/standby mode. This example assumes that you have deployed services in two Alibaba Cloud zones within the same region.Architecture:
  • Key conditions:
    • Data Center A has the same RDS clusters as Data Center B.
    • DTS is available to synchronize data between RDS instances to ensure data consistency.
  • Data backup and recovery:
    • DTS must be stable and run properly to ensure real-time data synchronization. If a fault occurs, you must ensure the stability and accuracy of DTS data synchronization.
    • If a fault occurs on Data Center A or the databases in Data Center A, traffic is directed to Data Center B. The resources of Data Center A remain unavailable if the fault persists. After Data Center A is recovered, you can specify it as a secondary zone.
    • If a fault occurs on the applications, traffic is directed to Data Center B. A check must be performed to ensure the consistency of data segments between data centers A and B. After the check is completed, the databases in Data Center B becomes primary databases, and the databases in Data Center A becomes secondary databases. In this scenario, data is synchronized from Data Center B to Data Center A.
    • You must configure DTS transmission links to synchronize data between RDS instances.
  • Features:
    • Advantages: ultra-high performance, automatic switchover, and fewer manual operations.
    • Disadvantages: 50% resource utilization rate.

Active/active mode

An example is used to introduce the architecture of the active/active mode. This example assumes that you have purchased two simplified IT systems in an Alibaba Cloud region.Architecture:
  • Key conditions:
    • Two simplified IT systems are deployed in two zones (data centers A and B) of the same Alibaba Cloud region. Both data centers are primary zones.
    • You can deploy Alibaba Cloud DNS, SLB, and ECS to meet your domain management, traffic distribution, and cloud computing needs, respectively. You can deploy Alibaba Cloud RDS to meet your database needs.
    • DTS is available to synchronize incremental data in real time and migrate data between databases.
  • Data backup and recovery:
    • If Data Center A works properly, you can use DTS to synchronize production data from the databases in Data Center A to the databases in Data Center B. You can also use DTS to check the consistency of data between the databases.
    • If a fault occurs on Data Center A, Alibaba Cloud DNS resolves traffic to Data Center B, and the production data is stored in the databases in Data Center B.
  • Features:
    • Advantages: achieves a higher resource utilization rate than the active/standby mode does.
    • Disadvantages: cross-zone latency and manual switchover. If a fault occurs on Data Center A, a latency occurs when users access applications from Data Center B.