AWS API Gateway is extremely powerful and easy to deploy. You don’t have to manage any infrastructure (i.e. no purchasing, scaling, patching), the gateway is capable of handling tens of thousands of requests per second, and you only pay a very small price based on the number of requests served . In addition, it also provides many other functionalities, such as managed websocket support.
One of these lesser-known, but potentially very useful, functionalities of API Gateway is its service integrations, which give you the ability to connect API gateway directly to other AWS services, such as dynamodb, sqs, step functions or sns (not just lambda). A standard pattern is API gateway -> lambda -> sns (or some middleware or end point service such as S3, DynamoDB, SQS etc.)
With this approach, API gateway triggers a (nodejs) lambda, which performs validation, and if the request is valid, it publishes an event to the sns topic.
The folder containing all of the project code including the SAM or Serverless Application Model template which provisions the architecture can be found here.
Here is the evaluation of this design using the six pillars
reliability
cost optimization
NOTE: this could accrue negligibly more cost than API gateway directly to lambda, but this is likely only a few cents per month. You refer to the Cost Evaluation section for more analysis.
Default is to use API gateway -> lambda -> middleware (i.e. sns).
While this architecture might incur slightly more cost and slightly more overhead, the p99 latency is still under 300ms, and the benefits given by this solution outweigh these slight drawbacks.
Some of these benefits include the flexibility of doing custom (or more complex) validation, the saving of engineer’s time, as they can use whatever language they like within AWS lambda instead of learning how to transform requests using apache templates in cloudformation, as well as the ability to provide clients with more helpful error messages, as well as all error messages at once (this saves them from getting frustrated and leaving our site, or at least saves us from them making multiple calls).
The one drawback to watch out for is if this lambda is called frequently and it ends up consuming a lot of concurrency, some ways to mitigate this include:
The only time to use an API gateway direct service integration is if the API is extremely high traffic and we are concerned about saving a few dollars, or we see throttles on synchronously invoked functions which cannot be made asynchronous.
