With gp3 set as storage type can no longer change between plans in Tanzu Cloud Service Broker for AWS

Products

• Cloud Services Products

Issue/Introduction

With gp3 set as storage type can no longer change between plans in Tanzu Cloud Service Broker for AWS. 
CSB can create a db/db's on the plans but when customer try to change between plans it gives the error: 

ModifyDBInstance, https response error StatusCode: 400, RequestID: 8180774f-c14b-427a-bc1b-14e32f57ac2f, api error InvalidParameterCombination: You can't specify IOPS or storage throughput for engine postgres and a storage size less than 400.\n\n with aws_db_instance.db_instance,\n on main.tf line 50, in resource \"aws_db_instance\" \"db_instance\":\n 50:

That's with storage size below 400GB and with the iops set to zero due to earlier known issue that instance may fail to create with this error if storage_type is set to gp3 and storage_gb is less than a 400 GB event when iops is not specified.

Resolution

This seems to be an issue with the AWS API not being consistent in behaviour regarding IOPS with create and update operations. Creating instances with an IOPS value of 0 is interpreted as not setting a value whilst updating it is interpreted by the API as trying to set 0 as value.

This issue is fixed in Cloud Service Broker for AWS version 1.8.1:

• Some RDS MySQL and PostgreSQL instances using gp3 and io1 storage cannot be updated: You can now specify a value of null instead of 0 for iops, this allows for creation and update of instances with storage_gb < 400GB.