Aws-sam-cli: No log file is written with --log-file or -l

Created on 17 Sep 2017 · 5Comments · Source: aws/aws-sam-cli

When I run start-api using this command (or variants):

sam local start-api --log-file ./out.log

Variants tried:

sam local start-api --log-file=./out.log
sam local start-api --log-file out.log
sam local start-api --log-file=out.log
sam local start-api -l ./out.log

no output file is written (nor created), and no error message is displayed.
My handler's return value is displayed in the console as expected.

template.yaml:

AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: My first serverless application.

Resources:

  Products:
    Type: AWS::Serverless::Function
    Properties:
      Handler: products.handler
      Runtime: python3.6
      FunctionName: products_handler
      CodeUri: ./dist
      Events:
        ListProducts:
          Type: Api
          Properties:
            Path: /products
            Method: get
        Product:
          Type: Api
          Properties:
            Path: /products/{product}
            Method: any

Test case:

import logging
LOGGER = logging.getLogger(__name__)
LOGGER.setLevel(logging.INFO)

def handler(event, context):
  LOGGER.error("Test message")
  return {'body': "some output\n"}

Command:

curl http://localhost:3000/products

If I set my logger to log to stdout/stderr (using logging.StreamHandler), I do see log message on the console,
but not using the aforementioned method (nor using any file-based ones, either, which I wouldn't expect to work anyway.)

Everything else works.

What am I missing?

typbug

Source

sthware

👍1

Most helpful comment

Change merged. Pending release

sanathkr on 24 Oct 2017

👍3

All 5 comments

Can you try print("foo") and tell me if it appears in log file? This should work unless the Docker container somehow intercepts the Logger output stream. If not, there is a bug in setting up the log stream.

sanathkr on 21 Sep 2017

Running with sam local start-api --log-file ./out.log

print('foo')

goes directly to the console

sthware on 21 Sep 2017

I can confirm that no log file is created. I also tried several ways to generated logs and none of them are written to a file.
If I search through the code, I actually can't find any reference to this option, other than in main.go where it is listed as a possible option. Perhaps am I overlooking it, but it seems like during some refactoring this got removed.