Set the Lambda Handler String

The handler tells Lambda which file and exported function to invoke. The format is "filename.exportedFunctionName" for most runtimes. Getting this wrong means Lambda deploys but returns a "Runtime.HandlerNotFound" error on every invocation.

Paste into this field

Lambda → handler

Output looks like

index.handler or src/handler.main or app.lambda_handler (Python)

1Handler format by runtime

Node.js: FILE_WITHOUT_EXTENSION.EXPORTED_FUNCTION_NAME

index.handler → file: index.js (or index.mjs), export: handler

src/handler.main → file: src/handler.js, export: main

Python: FILE_WITHOUT_EXTENSION.FUNCTION_NAME

app.lambda_handler → file: app.py, function: lambda_handler

Java: PACKAGE.CLASS::METHOD

com.example.Handler::handleRequest

9Enter in CloudStack Canvas

Select your Lambda node → property panel → "Handler" field → enter the handler string matching your deployment package.

11Verify after deploy

After deploying, test the function in the Lambda console. If you see "Runtime.HandlerNotFound", the handler string does not match your file/export name.

Once you have the value, go back to CloudStack Canvas and paste it into the highlighted field.

CloudStack Canvas · Validation Guide