Question 1

How do I debug a Lambda function locally with SAM CLI?

Accepted Answer

Use `sam local invoke` with the --debug-port flag to attach a debugger (e.g., for Python or Node.js) in a Docker container. This mimics the AWS environment, allowing breakpoints and step-by-step inspection in your IDE.

Question 2

SAM CLI vs Serverless Framework: which is better?

Accepted Answer

SAM CLI is tightly integrated with AWS CloudFormation and excels at local testing with Docker, while Serverless Framework supports multiple clouds and has a larger plugin ecosystem. Choose SAM for AWS-native projects and Serverless for multi-cloud or extensive community plugins.

Question 3

Can I use SAM CLI with AWS CDK?

Accepted Answer

Yes, SAM CLI supports testing and deploying applications defined with AWS CDK, as mentioned in the README for local testing on CDK applications. Use `sam build` and `sam deploy` with CDK-generated CloudFormation templates.

Question 4

What are the limitations of SAM local testing?

Accepted Answer

Local testing may not perfectly replicate cloud behavior for services like DynamoDB streams or X-Ray traces, and it requires Docker running. Some AWS features, such as IAM roles or VPC configurations, have limited emulation.

Question 5

How to handle environment variables in SAM local testing?

Accepted Answer

Define environment variables in your SAM template under the Function properties, and they'll be loaded automatically with `sam local invoke`. You can also override them via command-line options or external files for testing.

Question 6

Does SAM CLI support custom Lambda runtimes?

Accepted Answer

Yes, SAM CLI can build and test custom runtimes using the `sam build` command with appropriate configurations, as it leverages Lambda builders for supported runtimes and custom workflows.

aws-sam-local

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