Lambda-to-Lambda Calls vs. SNS Chaining in AWS: When and How to Use Each
Modern serverless architectures often require connecting multiple AWS Lambda functions. Two common patterns are direct Lambda-to-Lambda invocation and chaining via Amazon SNS. This post explains when to use each, with diagrams, CloudFormation templates, and TypeScript code for both approaches.
When to Use Each Pattern
Choosing between direct Lambda-to-Lambda calls and SNS chaining depends on your workflow’s requirements for coupling, reliability, and scalability. While it is technically possible to invoke one Lambda function from another, it is important to understand the implications of doing so synchronously. Synchronous Lambda-to-Lambda calls—where the first function waits for a response from the second—are generally discouraged as a best practice. This is because they can lead to increased latency, higher costs, and more complex error handling, especially if the downstream Lambda experiences throttling or failures. In most cases, tightly coupled, synchronous workflows are better implemented using other AWS services such as Step Functions, which are designed for orchestrating distributed processes with built-in error handling and state management.