Lambda Concurrency And Throttling

• AWS Lambda has 1000 invocations concurrently at a given time per region.
• To limit / throttle the concurrency, we can set Lambda Reserved Concurrency at the function level

Error handling

• If function doesn't have enough concurrency available, next requests are throttle
• For throttle error (429) and system errors (500s), lambda returns event to the event queue to try again for up to 6 hours
  • Retry using exponential back off from 1 second - 5 minutes after first attempt