Modifying DCS Instance 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, create an instance, migrate data, and switch IPs. For details, see Migrating Instance Data.

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, 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, out/in	Scaling up/down and replica quantity change
  Redis 6.0	Scaling up/down	Scaling up/down and replica quantity change	-	-	-

• 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 or later 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 increasing the size per shard: Insufficient memory of the node's VM will cause the node to migrate. Service connections may stutter and the instance may become read-only during the migration. Increasing the node capacity when the VM memory is sufficient does not affect services. 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.

Changing an Instance

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 of the Operation column in the row containing the DCS instance.
5. On the Modify Specifications page, select the desired specification.
6. Click Next. Confirm the change details and view the risk check results.
   If any risk is found in the check, the instance may fail to be modified. For details, see Table 4.

   Table 4 Risk check items

   Check Item	Reason for Check	Solution
   Non-standard configuration check NOTE: Check whether the following items meet standards: Bandwidth of a single instance node Memory of a single instance node Replica quantity of Redis Cluster instances Proxy quantity of Proxy Cluster instances maxclients of Proxy Cluster instances (maximum allowed connections exceeded)	If your instance has non-standard configurations, the console displays a message indicating that they will be converted to standard during the change. You can retain non-standard bandwidth or proxy quantity configuration only.	If your instance does not have non-standard configurations, the check result is normal and no action is required. If the instance has non-standard configurations, determine whether to proceed with the change or whether to retain the non-standard bandwidth and proxy quantity configuration.
   Node status	Abnormal instance nodes cause instance modification failures.	If this case, contact customer service.
   Dataset memory distribution check NOTE: This check item applies only to Proxy Cluster and Redis Cluster instances.	Specification modification of a cluster instance involves data migration between nodes. If an instance has any key bigger than 512 MB, the modification will fail when big key migration between nodes times out. If the instance dataset memory is unevenly distributed among nodes and the difference is greater than 512 MB, the instance has a big key and the change may fail.	before proceeding with the change.
   Memory usage check	If the memory usage of a node is greater than 90%, keys may be evicted or the change may fail.	If the memory usage is too high, optimize the memory by optimizing big keys, scanning for expired keys, or deleting some keys.
   Network input traffic check NOTE: This check item applies only to single-node, read/write splitting, and master/standby instances.	The change may fail if the network input traffic is too heavy and the write buffer overflows.	Perform the change during off-peak hours.
   CPU usage check	If the node CPU usage within 5 minutes is greater than 90%, the change may fail.	Perform the change during off-peak hours.
   Resource capacity NOTE: This item should be checked only when scaling up cluster instances.	To scale up a cluster instance, if the VM resource capacity is insufficient, the node needs to be migrated during the change. Service connections become intermittent or read-only during the migration.	If the resource capacity check poses risks, ensure that your application can reconnect to Redis or handle exceptions, you may need to restart the application after the change.

   

   • If the check results are normal, no risks are found in the check.
   • If the check fails, the possible causes are as follows:
     • The master node of the instance fails to be connected. In this case, check the instance status.
     • The system is abnormal. In this case, click Check Again later.
   • Click Stop Check to stop the check. Click Check Again to restart the check.
   • If you want to proceed with the change despite risks found in the check or after clicking Stop Check, select I understand the risks.

7. Click Next, confirm the details, and click Submit. After the modification is submitted, you can go to the Background Tasks page to view the modification status.

   Click the task name on the Background Tasks page to view task details. After an instance is successfully modified, it changes to the Running state.

   Figure 1 Viewing background task details
   
   

   • If the specification modification of a single-node DCS instance fails, the instance is temporarily unavailable. 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 still uses 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.
   • Specification modification of a single-node, master/standby, or read/write splitting DCS instance takes 5 to 30 minutes to complete, while that of a cluster DCS instance takes a longer time.