Thanks, I will fix the broken links :-)

The tech is completely hosted on AWS, and it is entirely "serverless". So the core is using the API Gateway + Lambda + DynamoDB. Additionally, I use Kinesis Firehose + S3 to process internally generated data such as billing events. Athena helps me to query the data if needed.

Basically, the scalability & high availability is entirely provided by AWS and the pricing model matches almost 1-to-1 the pricing by AWS.

If you have any specific questions about the tech, I can answer them.