A refactor changed one output prefix in an image processing Lambda, and the function started triggering itself. Invocations went from 40,000 a day to 9 million in six hours. We stopped it with reserved concurrency, then separated input and output and added loop guards.
SQS, SNS and EventBridge all move messages on AWS, and teams often pick whichever they used last. We compare them on what actually differs: pull versus push, fan-out, filtering, ordering, retries and replay, then show the combinations we use in production.
Every deploy and every traffic burst, the first requests to our booking API timed out and Postgres started refusing clients. The handler did heavy setup and opened a fresh connection per invocation. Moving init out of the handler and adding RDS Proxy fixed it.
A Lambda function that converts uploaded videos to thumbnails worked for the first few invocations, then failed with No space left on device. Files written to /tmp survived across warm invocations of the same execution environment and filled the 512 MB default. How we found it and fixed cleanup, sizing and streaming.
Our order fulfilment state machine ran for months, then failed for large orders with States.DataLimitExceeded. A Map state collected per-item results into one array that crossed the 256 KiB payload limit. How we found the state that grew, trimmed outputs with ResultSelector and moved bulk data to S3.