Set appendonly flag in Elasticache Parameter Group

In Amazon ElastiCache, parameters have attributes that determine whether they can be modified or not. The appendonly parameter has an IsModifiable attribute set to false, which means you cannot modify this parameter after the parameter group is created.

When you create a parameter group, it initially has the family's default values. For parameters that cannot be modified (where IsModifiable is false), you cannot change these values even after creating the parameter group.

For Valkey or Redis OSS, some parameters require specific handling. If you need to use a different value for the appendonly parameter than what's provided in the default parameter group, you would typically need to:

1. Create a manual backup of your existing cluster (if applicable)
2. Delete the cluster
3. Restore the cluster using a parameter group with the desired settings and your backup to seed the new cluster

However, since the appendonly parameter is not modifiable, you may need to check if there's a specific parameter group family for Valkey 8 that has this parameter set to true by default, or contact AWS Support for assistance with this specific requirement.

Parameter values are applied to clusters associated with the parameter group, but only modifiable parameters can be changed from their default values. Since appendonly is marked as not modifiable, you won't be able to edit this value in the ElastiCache console or through the API.
Sources
Parameter - Amazon ElastiCache
Modifying an ElastiCache parameter group - Amazon ElastiCache
Parameter management in ElastiCache - Amazon ElastiCache
Creating an ElastiCache parameter group - Amazon ElastiCache