#lambda

Cloud & Infrastructure Bug Report

Users randomly could not log in: our Cognito post-authentication Lambda exceeded the 5-second limit

Tomás Herrera · Jul 23, 2026 · 7 min read

A few percent of logins failed with a generic error after we added a Cognito post-authentication trigger that recorded login events in our database. The Lambda ran in a VPC, opened a database connection on cold start, and sometimes exceeded Cognito's 5-second trigger timeout. How we moved the work off the login path.

Cloud & Infrastructure Bug Report

Step Functions failed with States.DataLimitExceeded: keeping state payloads under 256 KiB

Tomás Herrera · Mar 3, 2025 · 8 min read

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.

Cloud & Infrastructure Bug Report

SNS to SQS fan-out delivered our JSON as an escaped string inside an envelope: raw message delivery

Tomás Herrera · Dec 8, 2024 · 8 min read

We put SNS in front of an SQS queue to fan out order events, and the consumer Lambda started failing with KeyError: 'orderId'. Each SQS message body was now an SNS envelope with our event as an escaped JSON string in Message. How raw message delivery fixes it, and what changes for filtering and attributes.