Updated on 2025-05-22 GMT+08:00

RES03-01 Deploying Clusters Across AZs

All components in an application are deployed across AZs for DR to prevent service interruptions in case of a single-AZ fault.

  • Risk level

    High

  • Key strategies
    • If a cloud service supports cross-AZ HA instances, use the cross-AZ HA instances of the cloud service first.
    • If a cloud service supports only single-AZ instances and does not support cross-AZ HA instances, use other cloud services or the application layer for cross-AZ DR. The following uses ECS as an example:
      • For stateless ECSs, use the cross-AZ scaling capability of AS or the cross-AZ load balancing capability of ELB for cross-AZ HA. If an AZ is faulty, services can be automatically and quickly switched over to another available AZ.
      • For stateful ECSs or BMSs, you are advised to implement cross-AZ DR at the application layer. Use automatic cross-AZ switchover or DR management tools for automatic DR switchover to reduce manual operations during disasters.

    To reconstruct a deployed application system to a cross-AZ instance, perform the following steps:

    1. Determine the key components of the application system. If a key component is faulty, the entire application system or key functions will be affected.
    2. Check the cross-AZ HA capability of the key components. Ensure that services of key components can automatically switch to another AZ during failures for seamless recovery.
    3. Optimize the key components that do not support HA as follows:
    • For services like RDS, DDS, and DCS that support cross-AZ HA instances and support reconstruction to cross-AZ HA instances, upgrade the single-AZ instances to cross-AZ instances.
    • For services like dedicated ELB, CCE clusters, DMS, and OBS buckets that support cross-AZ HA instances but cannot be reconstructed to cross-AZ HA instances, apply for new cross-AZ HA instances to replace the single-AZ instances.
    • For services like ECS using single-node instances, apply for multiple instances in multiple AZs to bear a service, and use cross-AZ ELB for cross-AZ load balancing and failover. Alternatively, use failover of cross-AZ instances at the application layer for cross-AZ HA.
  • Related cloud services and tools

    Most cloud services of Huawei Cloud support multi-AZ instances, such as ELB, AS, CCE, DCS, DMS, RDS, and GaussDB. If one AZ is faulty, the other AZ can quickly take over services to keep services running smoothly.