Modifying Specifications

Change of the Instance Type

Any instance type changes not listed in the preceding table are not supported. To modify specifications while changing the instance type, see IP Switching.

For details about the commands supported by different types of instances, see Command Compatibility.

Scaling

• Scaling options

  Table 2 Scaling options supported by different instances

  Cache Engine	Single-Node	Master/Standby	Redis Cluster	Proxy Cluster	Read/Write Splitting
  Redis 4.0	Scaling up/down	Scaling up/down and replica quantity change	Scaling up/down, out/in, and replica quantity change	Scaling up/down and out/in	Scaling up/down and replica quantity change
  Redis 5.0	Scaling up/down	Scaling up/down and replica quantity change	Scaling up/down, out/in, and replica quantity change	Scaling up/down and out/in	Scaling up/down and replica quantity change
  Redis 6.0	Scaling up/down	Scaling up/down	-	-	-

• Impact of scaling

  Table 3 Impact of scaling

  Instance Type	Scaling Type	Impact
  Single-node , read/write splitting, and master/standby	Scaling up/down	During scaling up, a DCS Redis 4.0/5.0/6.0 instance will be disconnected for several seconds and remain read-only for about 1 minute. During scaling down, connections will not be interrupted. For scaling up, only the memory of the instance is expanded. The CPU processing capability is not improved. Single-node DCS instances do not support data persistence. Scaling may compromise data reliability. After scaling, check whether the data is complete and import data if required. If there is important data, use a migration tool to migrate the data to other instances for backup. For master/standby and read/write splitting instances, backup records created before scale-down cannot be used after scale-down. If necessary, download the backup file in advance or back up the data again after scale-down.
  Proxy Cluster and Redis Cluster	Scaling up/down	Scaling out by adding shards: Scaling out does not interrupt connections but will occupy CPU resources, decreasing performance by up to 20%. If the shard quantity increases, new Redis Server nodes are added, and data is automatically balanced to the new nodes, increasing the access latency. Scaling in by reducing shards: If the shard quantity decreases, nodes will be deleted. Before scaling in a Redis Cluster instance, ensure that the deleted nodes are not directly referenced in your application, to prevent service access exceptions. Nodes will be deleted, and connections will be interrupted. If your application cannot reconnect to Redis or handle exceptions, you may need to restart the application after scaling. Scaling up by shard size without changing the shard quantity: Currently unavailable. Scaling down by reducing the shard size without changing the shard quantity has no impact. To scale down an instance, ensure that the used memory of each node is less than 70% of the maximum memory per node of the new flavor. The flavor changing operation may involve data migration, and the latency may increase. For a Redis Cluster instance, ensure that the client can process the MOVED and ASK commands. Otherwise, the request will fail. If the memory becomes full during scaling due to a large amount of data being written, scaling will fail. Before scaling, check for big keys through Cache Analysis. Redis has a limit on key migration. If the instance has any single key greater than 512 MB, scaling will fail when big key migration between nodes times out. The bigger the key, the more likely the migration will fail. Before scaling a Redis Cluster instance, ensure that automated cluster topology refresh is enabled. If it is disabled, you will need to restart the client after scaling. For details about how to enable automated refresh if you use Lettuce, see an example of using Lettuce to connect to a Redis Cluster instance. Backup records created before scaling cannot be used. If necessary, download the backup file in advance or back up the data again after scaling.
  Master/standby, read/write splitting, and Redis Cluster instances	Scaling out/in (replica quantity change)	Before adding or removing replicas for a Redis Cluster instance, ensure that automated cluster topology refresh is enabled. If it is disabled, you will need to restart the client after scaling. For details about how to enable automated refresh if you use Lettuce, see an example of using Lettuce to connect to a Redis Cluster instance. Deleting replicas interrupts connections. If your application cannot reconnect to Redis or handle exceptions, you may need to restart the application after scaling. Adding replicas does not interrupt connections. If the number of replicas is already the minimum supported by the instance, you can no longer delete replicas.

Procedure

1. Log in to the management console, and choose Application > Distributed Cache Service in the service list.
2. Click in the upper left corner of the management console and select the region where your instance is located.
3. In the navigation pane, choose Cache Manager.
4. Choose More > Modify Specifications in the row containing the DCS instance.
5. On the Modify Specifications page, select the desired specification.
6. Click Next, confirm the details, and click Submit.

   You can go to Background Tasks page to view the modification status. For more information, see Viewing Background Tasks.

   Specification modification of a single-node, master/standby, or read/write splitting DCS instance takes about 5 to 30 minutes to complete, while that of a cluster DCS instance takes a longer time. After an instance is successfully modified, it changes to the Running state.

   Go to the Background Tasks page to view task details.

   Figure 1 Viewing background task details
   
   

   • If the specification modification of a single-node DCS instance fails, the instance is temporarily unavailable for use. The specification remains unchanged. Some management operations (such as parameter configuration and specification modification) are temporarily not supported. After the specification modification is completed in the backend, the instance changes to the new specification and becomes available for use again.
   • If the specification modification of a master/standby or cluster DCS instance fails, the instance is still available for use with its original specifications. Some management operations (such as parameter configuration, backup, restoration, and specification modification) are temporarily not supported. Remember not to read or write more data than allowed by the original specifications; otherwise, data loss may occur.
   • After the specification modification is successful, the new specification of the instance takes effect.