aws lambda - aws-sam-local environment variables

Question

I am following the readme here: https://github.com/awslabs/aws-sam-local

I have a lambda written in python 3.6 and its similar to the helloworld example here : https://github.com/awslabs/aws-sam-local/tree/develop/samples/hello-world/python

template.yml looks as such:

AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: MyFunction1 API
Resources:
  MyFunction1:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: MyFunction1
      Handler: lambda_module.lambda_handler
      Runtime: python3.6
      CodeUri: lambda.zip
      MemorySize: 128
      Timeout: 10
      Policies:
        -AWSLamdbaBasicExecutionRole
      Events:
        BingLambdaEndpoint:
          Type: Api
          Properties:
            Path: MyFunction1/search
            Method: get

I have environment variables within the lambda but not able to wire them up on start up. Documentation says I can create a environments.json file and append the following on the invoke command : Use --env-vars argument of invoke

My environment file looks like the example and I get an error: Unable to find environment variable: api_key

environment.json looks as such:

{
  "MyFunction1": {
    "api_key": "123456789",
    "BUCKET_NAME": "testBucket"
  }
}

command I run is as such:

sam local invoke MyFunction1 --env-vars environment_variables.json -e event.json

Can anyone provide additional insight?

Answer 1

Any environment variables you want to use with SAM Local in this manner need to exist in your SAM template. From this GitHub issue:

... SAM Local only parses environment variables that are defined in the SAM template.

In the template, you can provide no value, an empty string, or choose a sensible default.

A portion of a template including environment variables:

Resources:
  MyFunction1:
    Type: 'AWS::Serverless::Function'
    Properties:
      .....
      Environment:
        Variables:
          api_key:
          BUCKET_NAME:

---

You can think of the environment variables file as a mechanism to override environment variables that the template "knows" about. It does not work as a mechanism to inject arbitrary environment variables into the local runtime.