Managed Postgres RDS Migration to Managed Postgres RDS

Question

We have a very large database that has been cleaned up and the size reduced from 35Tb to ~7Tb and have attempted to initiate a DMS as no other options are able to maintain up time adequately. We have implemented the parameters indicated here -> https://docs.aws.amazon.com/dms/latest/userguide/dm-data-providers-source-postgresql.html
Both instances are configured to use the master account and are configured in the same VPC, but we keep getting a failure with the following message. "The prerequisites for DMS to use the source database have not been met. Configure the user account permissions or privileges for DMS and restart the migration." IS there an underlying issue? Is this related to IAM?
We implemented this -> https://docs.aws.amazon.com/dms/latest/userguide/dm-iam-resources.html

Answer

Hello.

I think DMS was reading password information from Secrets Manager.  
Therefore, it is possible that an error may occur if the appropriate IAM policy is not set.

In my experience, a common problem was that the security group settings were not set properly and the DMS could not connect to the database.  
Therefore, please check whether the security group on the PostgreSQL side allows access from DMS.  
https://docs.aws.amazon.com/dms/latest/userguide/dm-network.html

Can you check the error message by following the steps in the document below?  
https://docs.aws.amazon.com/dms/latest/userguide/dm-troubleshooting.html#dm-troubleshooting-dm-fails  
> Check the error message for your data migration in the AWS DMS console. To do so, open your migration project, and choose your data migration. On the Details tab, check the Last failure message under General.

Managed Postgres RDS Migration to Managed Postgres RDS

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