I watched a good video on AWS DMS - a couple of years old - but good fundamentals . Suitable as an introduction - explaining use cases & reasons to use AWS DMS

AWS re:Invent 2021 - Dive deep into database migration services AWS DMS and AWS SCT

Why migrate from on-prem to AWS cloud ?   there are various reasons typically part of a larger strategic initiative

-hardware end of life 

-lack of redundancy or automation - e.g multi-availability zone

-Failure at different layers

-Scalability 

-Cost optimization

-Fully managed

Tooling 

-AWS Schema Conversion Tool (AWS SCT) - attempts\facilitates to convert source schema, stored procedures & functions into the target language

-AWS Database Migration Service (AWS DMS)  - fully managed service on AWS. Helps to migrate database from one location to another , a one-time bulk load and maintain near consistency , and help in .

Babelfish Compass Tool - The Babelfish Compass Tool is an assessment tool for compatibility between SQL Server & Babelfish.    

Supports different usage patterns : 

1) A one-time load   

 2)  One time bulk load , maintain consistency and then when in synch failover. 

For usage patterns 2) - one time bulk load and capturing on-going changes (aka ongoing replication or CDC). Each source endpoint engine type will require some reconfiguration to expose the change stream.    AWS DMS uses the db engine types API, for example SQL Server would utilises MS SQL Server CDC

-Homogenous versus Heterogenous 

Homogenous = Relational to Relational -( same database format)        or NoSQL to NoSQL (same database format)  . e.g PostgreSQL to Aurora PostgreSQL

Heterogenous = Relational to Relational (different format) or NoSQL to NoSQL (different format)   e.g   Oracle to MySQL

-Step 1: Convert or copy your schema

-Step 2 : Move your data 

Plan, assess and convert

        - database migration assessment report 

         -convert    

Empty database , then use DMS to migrate data. 

What is a DMS instance?

Behind the scenes when you launch a replication task and EC2 instance is utilized with replication software installed. 

-Start a replications instance - AWS DMS creates the replication instance on an AWS EC2 instance. The replication instance does the actual data migration between the source endpoint and target endpoint. The size of the replication instance will depend on a number of factors including how much data needs to be migrated  & duration.

-Concept of endpoints  - Connect to source & target databases . 

                               - configuration of a network - 1) target & source both on same VPC  2)  source on on on-premises & target on AWS VPC

-Database migration Tasks - Select tables , schemas or databases

-AWS DMS load data and keep them in synch

-Test replication - test the expected behaviour post replication

-Switch applications over to the target after they are in synch at a suitable time

-AWS DMS captures ongoing changes after initial migrations using CDC - DMS watches the sources

-All data stored using KMS encryption

Use cases

-Fan out microservices architectures

-General use cases

         - Migrate business critical applications

         -Archive old data to Amazonn s3

        - Migrate from NoSQL to SQL,SQL to NoSQL,or NoSQL to NoSQL

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