Lambda function timeout

Lambda Timeout Error from AWS access denied errors is often more complex than a missing IAM permission — resource-based policies, service control policies (SCPs), and permission boundaries all interact to determine effective permissions. The IAM Policy Simulator (in the AWS Console under IAM) evaluates effective permissions for a given principal, action, and resource — it shows exactly which policy allows or denies the action. For cross-account access, simulate from both accounts. Common sources of unexpected denials beyond IAM identity policies: S3 bucket policies that require aws:SecureTransport: true (HTTPS-only) will deny SDK requests that default to HTTP in older SDK versions. KMS key policies that do not explicitly allow the calling principal's account will deny decrypt operations. Organizations SCPs that restrict to specific regions or services override IAM policies — check SCPs with aws organizations list-policies-for-target. VPC endpoint policies can restrict which AWS services are accessible from within a VPC. Run aws sts get-caller-identity to confirm which principal is making requests before debugging policy configurations.