What could prevent a successful change of RDS instance specifications?

Changing the specifications of an RDS (Relational Database Service) instance can be impacted by various operational conditions. When a backup task is being executed on the instance, it typically locks certain resources and operations, causing restrictions on modifying the instance specifications. During a backup process, the system prioritizes data integrity and availability, which can prevent changes such as scaling up or down the resources allocated for the instance.

In contrast, while an actively processing instance may also appear to be a limitation, it typically allows for some degree of flexibility in specification changes, provided that the database management system supports dynamic scaling. Reaching maximum storage is a constraint but does not inherently block changes to instance specifications unless the change requires additional storage. Lastly, the type of billing model (pay-as-you-go or subscription) generally should not affect the ability to change specifications, as these actions are more related to the underlying infrastructure capabilities. Thus, the presence of an executing backup task stands out as the primary reason for preventing a successful change in RDS instance specifications.