Module aws_lambda_powertools.middleware_factory.factory

Functions

def lambda_handler_decorator(decorator: Callable | None = None, trace_execution: bool | None = None) ‑> Callable

Decorator factory for decorating Lambda handlers.

You can use lambda_handler_decorator to create your own middlewares, where your function signature follows: fn(handler, event, context)

Custom keyword arguments are also supported e.g. fn(handler, event, context, option=value)

Middlewares created by this factory supports tracing to help you quickly troubleshoot any overhead that custom middlewares may cause - They will appear as custom subsegments.

Non-key value params are not supported e.g. fn(handler, event, context, option)

Environment Variables

POWERTOOLS_TRACE_MIDDLEWARES : str uses Tracer to create sub-segments per middleware (e.g. "true", "True", "TRUE")

Parameters

decorator : Callable

Middleware to be wrapped by this factory

trace_execution : bool

Flag to explicitly enable trace execution for middlewares.

Env POWERTOOLS_TRACE_MIDDLEWARES="true"

Example

Create a middleware no params

from aws_lambda_powertools.middleware_factory import lambda_handler_decorator

@lambda_handler_decorator
def log_response(handler, event, context):
    any_code_to_execute_before_lambda_handler()
    response = handler(event, context)
    any_code_to_execute_after_lambda_handler()
    print(f"Lambda handler response: {response}")

@log_response
def lambda_handler(event, context):
    return True

Create a middleware with params

from aws_lambda_powertools.middleware_factory import lambda_handler_decorator

@lambda_handler_decorator
def obfuscate_sensitive_data(handler, event, context, fields=None):
    # Obfuscate email before calling Lambda handler
    if fields:
        for field in fields:
            field = event.get(field, "")
            event[field] = obfuscate_pii(field)

    response = handler(event, context)
    print(f"Lambda handler response: {response}")

@obfuscate_sensitive_data(fields=["email"])
def lambda_handler(event, context):
    return True

Trace execution of custom middleware

from aws_lambda_powertools import Tracer
from aws_lambda_powertools.middleware_factory import lambda_handler_decorator

tracer = Tracer(service="payment") # or via env var
...
@lambda_handler_decorator(trace_execution=True)
def log_response(handler, event, context):
    ...

@tracer.capture_lambda_handler
@log_response
def lambda_handler(event, context):
    return True

Limitations

• Async middlewares not supported
• Classes, class methods middlewares not supported

Raises

MiddlewareInvalidArgumentError

When middleware receives non keyword=arguments