This looks pretty reasonable overall, but it seems like it could have been implemented far more simply. It appears they are emailing PDF copies of stock market

This looks pretty reasonable overall, but it seems like it could have been implemented far more simply. It appears they are emailing PDF copies of stock market transactions to fulfill a regulatory requirement, so the PDF generation should be deterministic and email delivery of a receipt is an idempotent operation. Instead of all that scheduled orchestration complexity they could just queue their PDF jobs to SQS and do the work in a Lamba function, this would also let them queue the PDFs as the transactions are happening instead of continuing to run this as a nightly batch job. It's also unclear why render + sign + add to mail queue need to be 3 separate queued tasks. They have to execute serially, so a single worker could do the whole process and checkpoint to S3 after each step, or not because the output is deterministic anyway. It would also eliminate their issues with S3 request limits by keeping all the data relevant to a PDF local to 1 worker for the duration of processing.