streaming data through the DMS

Hi

Not necessary or mandatory have the same size and architecture, it depends how will be your requirements for your target database and type of workload of the source database. For example if your source database is focus to process thousands or millions of transactions, this workload needs to be replicated to your target database by DMS using CDC, transactions replicated needs to be received by your target database and process them, so, in this case you needs similar instance sizes. In another hand if your source is processing few transactions you target database could have less resources. You should analyze current transactional workload on your source database and define target size properly. Another thing to consider is the size of your DMS Instance, this instance should be on charge of replicate data from source to target, correct has to be set for replicate your data correctly, you could review link below to define DMS instance size.

Choosing the best size for a replication instance https://docs.aws.amazon.com/dms/latest/userguide/CHAP_BestPractices.SizingReplicationInstance.html

Regards