AWS Certified Solutions Architect - Professional 2020

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DynamoDB is not the same type of store as MongoDB

DynamoDB is a key value store with a capacity of 400KB. I don’t think it can be a direct replacement for MongoDB. Wouldn’t Amazon DocumentDB be a better choice here?

3 Answers

Hi Apurv,

Yes, DocumentDB would probably be something I’d choose over DynamoDB if I’m migrating from a MongoDB on-prem system.  However, DocumentDB was not one of the options in this question.  When solving for questions on the exam, you need to be sure you’re not writing your own answers but rather pick the best answer that you think AWS would endorse.   In this case, AWS will almost always push you toward managed services–hence why the DynamoDB answer is the best among the answers given…not necessarily the best given all other possible alternatives.


Suggested answer is just incorrect, you cannot migrate Mongo to Dynamo, even migrating to Document is a HUGE effort with a little chance of success. So that Option C should be the only way

Saed Alavinia

Without agreeing on if the answer chosen is the best answer or not, see here for how to migrate Mongo to Dynamo using DMS:

I agree that option C is actually the best answer.  Option D would also require heavy rewrite of applications that are coded to the mongodb API.  Those apps would have to be updated to use AWS SDK and start coding against dynamodb.  There is also not a one to one capability comparison between mongodb and dynamodb, so its not just a simple swap out of api calls.  It could actually require significant architecture and code changes which could take a while to deal with depending on how heavily mongo is actually used.  Not to mention the question doesn’t present the number of internal applications that use the mongodb.  Is it one app or 50?  C is the best way to make a migration initially with the potential to evaluate moving to dynamodb app by app in the future after. 

I’m doing into the pro exam tomorrow and hope to hell watching this course didn’t actually hurt my chances to pass.  I know about mongodb versus dynamodb because I’ve been a software engineer for a long time.  Its the things I don’t know about which I am using this course for that I am now worried about. Am I getting bad advice here?

Patrick Picard

how did it go?

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