What are the best Practices for Working with AWS Lambda Functions?

The following are recommended best practices for using AWS Lambda:

Write your Lambda function code in a stateless style, and ensure there is no affinity between your code and the underlying compute infrastructure.
Instantiate AWS clients outside the scope of the handler to take advantage of connection re-use.
Make sure you have set +rx permissions on your files in the uploaded ZIP to ensure Lambda can execute code on your behalf.
Lower costs and improve performance by minimizing the use of startup code not directly related to processing the current event.
Use the built-in CloudWatch monitoring of your Lambda functions to view and optimize request latencies.
Delete old Lambda functions that you are no longer using.