Reducing cross-AZ latency with the AWS Lambda metadata endpoint

AWS Lambda now exposes Availability Zone metadata through a metadata endpoint, enabling functions to discover their AZ ID and route to same-AZ resources to reduce cross-AZ latency and data transfer costs.

• Lambda metadata endpoint provides AZ ID (e.g., use1-az1) via authenticated HTTP request to reduce cross-AZ latency
• Available at no additional cost across all commercial AWS Regions, compatible with SnapStart, provisioned concurrency, and VPC functions
• Retrieve AZ ID using Powertools for AWS Lambda (Python, TypeScript, Java, .NET) or call endpoint directly with environment variables
• Route same-AZ reads to ElastiCache, RDS, Aurora, MemoryDB, EKS, and ECS resources while maintaining fallback paths
• AZ IDs (use1-az1) provide cross-account consistency unlike AZ names (us-east-1a) which vary per account
• Cache metadata at initialization, not per invocation, and refresh after SnapStart restore when AZ may change

Functions can now optimize latency-sensitive workloads by preferring same-AZ endpoints and implementing AZ-aware resilience patterns like targeted fault injection.