Troubleshoot execution issues in Lambda
When the Lambda runtime runs your function code, the event might be processed on an instance of the function that's been processing events for some time, or it might require a new instance to be initialized. Errors can occur during function initialization, when your handler code processes the event, or when your function returns (or fails to return) a response.
Function execution errors can be caused by issues with your code, function configuration, downstream resources, or permissions. If you invoke your function directly, you see function errors in the response from Lambda. If you invoke your function asynchronously, with an event source mapping, or through another service, you might find errors in logs, a dead-letter queue, or an on-failure destination. Error handling options and retry behavior vary depending on how you invoke your function and on the type of error.
When your function code or the Lambda runtime return an error, the status code in the response from Lambda is 200
OK. The presence of an error in the response is indicated by a header named X-Amz-Function-Error. 400
and 500-series status codes are reserved for invocation
errors.
Lambda: Execution takes too long
Issue: Function execution takes too long.
If your code takes much longer to run in Lambda than on your local machine, it may be constrained by the memory or processing power available to the function. Configure the function with additional memory to increase both memory and CPU.
Lambda: Logs or traces don't appear
Issue: Logs don't appear in CloudWatch Logs.
Issue: Traces don't appear in Amazon X-Ray.
Your function needs permission to call CloudWatch Logs and X-Ray. Update its execution role to grant it permission. Add the following managed policies to enable logs and tracing.
-
AWSLambdaBasicExecutionRole
-
AWSXRayDaemonWriteAccess
When you add permissions to your function, update its code or configuration as well. This forces running instances of your function, which have outdated credentials, to stop and be replaced.
Note
It may take 5 to 10 minutes for logs to show up after a function invocation.
Lambda: The function returns before execution finishes
Issue: (Node.js) Function returns before code finishes executing
Many libraries, including the Amazon SDK, operate asynchronously. When you make a network call or perform another operation that requires waiting for a response, libraries return an object called a promise that tracks the progress of the operation in the background.
To wait for the promise to resolve into a response, use the await keyword. This blocks your handler
code from executing until the promise is resolved into an object that contains the response. If you don't need to
use the data from the response in your code, you can return the promise directly to the runtime.
Some libraries don't return promises but can be wrapped in code that does. For more information, see Amazon Lambda function handler in Node.js.
Amazon SDK: Versions and updates
Issue: The Amazon SDK included on the runtime is not the latest version
Issue: The Amazon SDK included on the runtime updates automatically
Runtimes for scripting languages include the Amazon SDK and are periodically updated to the latest version. The current version for each runtime is listed on runtimes page. To use a newer version of the Amazon SDK, or to lock your functions to a specific version, you can bundle the library with your function code, or create a Lambda layer. For details on creating a deployment package with dependencies, see the following topics:
Python: Libraries load incorrectly
Issue: (Python) Some libraries don't load correctly from the deployment package
Libraries with extension modules written in C or C++ must be compiled in an environment with the same processor architecture as Lambda (Amazon Linux). For more information, see Working with .zip file archives for Python Lambda functions.