I'm using an AWS Lambda function that is triggered from an SNS event trigger to consume from an SQS queue. When the Lambda function executes, it pulls 10 messages from the queue, processes them, pulls another 10, and so on and so forth - up to a certain time limit that's coded into the Lambda function (less than the max of 5 minutes, obviously).
It's my understanding that a Lambda function triggered by an SNS event is one-to-one, is that correct? In other words, one SNS event won't trigger multiple Lambda functions (up to the maximum concurrent execution limit). There's no scaling based on load.
Are there any other potential solutions, leveraging Lambda, that would let me consume from SQS as frequently/fast as possible? I had considered trying to auto-scale my Lambda functions by leveraging CloudWatch alarms (and SNS event triggers) based on SQS queue size, but it seems like those alarms can fire, at most, every 5 minutes. I've also considered developing a master Lambda function that can automatically execute (many) slave Lambdas based on querying the queue size.
I understand that the more optimal design may be to leverage Kinesis instead of SNS. I may consider incorporating Kinesis in the future, but let's just pretend that Kinesis is not an option at this time.
There is no best way to do this. One approach (which you've kind of already mentioned) is to use CloudWatch and schedule a Lambda function to run every minute (that's the minimum schedule time for Lambda). This Lambda function will then look for new SQS messages and invoke other Lambda functions to handle new message(s). Here is a very good article for that use case: https://cloudonaut.io/integrate-sqs-and-lambda-serverless-architecture-for-asynchronous-workloads/
Personally, I do not recommend triggering your Lambda by SNS for this use case, because SNS doesn't give a full guarantee for delivery and recommend sending the SNS notifications to SQS - which does not solve your problem. From the FAQ's:
[...] If it is critical that all published messages be successfully processed, developers should have notifications delivered to an SQS queue (in addition to notifications over other transports).
Source: https://aws.amazon.com/sns/faqs/