aws dynamodb free tier practical limit

6
votes

As per AWS Dynamodb pricing it allows 25 read capacity units which translates to 50 GetItem requests per second ( with eventual consistency and each item being less than 4kb).

Free Tier*

As part of AWS’s Free Tier, AWS customers can get started with Amazon DynamoDB for free. DynamoDB customers get 25 GB of free storage, as well as up to 25 write capacity units and 25 read capacity units of ongoing throughput capacity (enough throughput to handle up to 200 million requests per month) and 2.5 million read requests from DynamoDB Streams for free.

How does this translate to online web site? If more than 50 users make GET calls at the same time, do the requests gets throttled ? and eventually 400 response is returned? Does it mean free tier practical limits are, during bursts if 100 users log in the site and make GET calls at same time, we may see 400 responses from DynamoDB. Is this valid conclusion?

I understand that there may hot be 100 requests per every second. But if the site has active users of more than 200 at any time, does Dydnamodb free tier still work?

1
amazon-web-servicesamazon-dynamodb
The intention of the AWS Free Usage Tier is to provide a means for customers to try various AWS services to better understand their capabilities. I don't think that the intention is to have people run production workloads on the Free Tier. You should be basing your capacity on the needs of your application and your customers, rather than trying to stay within free limits. – John Rotenstein
@JohnRotenstein This data is required for a startup applications. For a simple website with an approx 50 active users (always) logged into the site , was wondering if DynamoDB will cost more than App Engine Data store. I know each http request may result in more than 1 DynamoDB table Get calls in spite of Cache layer. I was trying to seek practical experience with DynamoDB on the limits for free tier. – suman j

1 Answers

9
votes

First, read up on DynamoDB burst capacity. Your DynamoDB tables should be able to sustain short bursts of higher throughput without throttling.

Second, the question of how database throughput capacity will "translate to online web site" is way too broad to answer directly. It entirely depends on how many database calls your web application makes per web request. Your question sounds like you are assuming every page load on your website results in exactly one DynamoDB request. That seems like an extremely unrealistic assumption.

You should be using a CDN to prevent as many requests as possible from even hitting your web server. You should be using a cache like Redis to prevent as many data lookups from hitting your database as possible. Then you should perform some benchmarking to determine the database throughput you are going to need, and evaluate that against the DynamoDB free tier.

How often does your web app content change? Do users submit changes to your content and if so, how often? These questions will directly affect how well your site can be cached, which will directly affect how often your app will have to go back to the database to get the latest content.

As for what response is returned to the user in the scenario where the DynamoDB request is throttled, that would be entirely dependent how you capture and handle errors in your web app.