.NET Localstack Returning Error When Trying to Provision a Dotnet8 Lambda - Stack Overflow

Tim Rabbetts | December 2, 2025

When working with AWS Lambda and .NET, developers often encounter various challenges, especially when using tools like Localstack for local development and testing. One common issue arises when trying to provision a .NET 8 Lambda function using Localstack, which may result in various errors that can be confusing and difficult to debug. In this article, we will explore the common problems developers face and discuss potential solutions.

Understanding Localstack

Localstack is a popular tool that allows developers to run AWS services locally. It is especially useful when developing Lambda functions, as it enables local testing without incurring costs or needing to deploy to AWS. However, Localstack is not a perfect replica of AWS, and this can lead to discrepancies and errors when provisioning resources.

Common Errors When Using .NET 8 with Localstack

When attempting to provision a .NET 8 Lambda in Localstack, developers may encounter various errors. Some common errors include:

  • Unsupported Runtime - Localstack may not support the .NET 8 runtime, depending on the version you are using.
  • Missing Permissions - Errors related to IAM roles and permissions that are not configured appropriately.
  • Invalid Function Configuration - Issues with the configuration file or incorrect settings in the function setup.
  • Networking Issues - Problems with how Localstack is networked or how ports are configured.

Troubleshooting Steps

To overcome these issues, the following troubleshooting steps can be helpful:

  • Check Localstack Version: Ensure you are using a version of Localstack that supports .NET 8. You can check the Localstack GitHub page for documentation on supported runtimes.
  • Proper Configuration: Review your Lambda function's configuration to ensure all required parameters are provided. This includes the handler, runtime, and role. Here is a simple example of a configuration:
    • {  "FunctionName": "MyDotnet8Lambda",  "Handler": "MyDotnet8Lambda::MyDotnet8Lambda.Function::FunctionHandler",  "Runtime": "dotnet8",  "Role": "arn:aws:iam::123456789012:role/service-role/your-role"}
  • Inspect IAM Roles: Verify that the IAM role assigned to your Lambda function has the necessary permissions. You can review your IAM policies in the Localstack dashboard or CLI.
  • Test with Logs: Enable logging for your Localstack setup to see the detailed error messages when an operation fails. This may provide insights into what is going wrong.
  • Network Configuration: Ensure that Localstack is properly networked, especially if running in a Docker container. Check your Docker settings and confirm that there are no port conflicts.

Example of Creating a .NET 8 Lambda in Localstack

To set up a .NET 8 Lambda function in Localstack, you could follow these steps:

  1. Create your .NET 8 Lambda project using the command line or Visual Studio.
  2. Publish your Lambda function to a specific folder:
    3. dotnet publish -c Release -o ./output
  3. Deploy the function using the Localstack CLI or AWS CLI pointed at Localstack.
    4. awslocal lambda create-function --function-name MyDotnet8Lambda --runtime dotnet8 --role arn:aws:iam::123456789012:role/service-role/your-role --handler MyDotnet8Lambda::MyDotnet8Lambda.Function::FunctionHandler --code S3Bucket=mybucket,S3Key=mycode.zip

Conclusion

Provisioning a .NET 8 Lambda function in Localstack can incur several common issues that require careful troubleshooting. By ensuring proper configuration, checking for version compatibility, and inspecting IAM roles, developers can mitigate most issues. Localstack is a powerful tool for local development, but understanding its limitations and quirks is essential for a smooth development experience.