Dynamo DB can be expected to adjust capacity every 5 minutes when set up with an auto scaling configuration or on pay-per-request model.
Lambda will scale up in seconds.
Dynamo, however, can be set not to (if you wish to stay within free tier limits). Dynamo DB free tier allows 5 4KB/key reads/second, with a buffer for about 5 minutes worth of "tokens" at this rate.
If poorly designed (e.g. using Dynamo like a relational database) you chew through this with app-side joins very quickly. Even if well designed, looking up related articles, or re-loading records on page transition will eat up DB time
As someone else mentioned, caching is critical for this setup to survive this load, especially if you want to stay in free tier... And CloudFront costs pennies compared to Dynamo and Lambda... Though both can easily be cheaper than $5/month
