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.

Answer 2

template file

AWSTemplateFormatVersion: '2010-09-09' Transform: AWS::Serverless-2016-10-31    Globals:    Function:     Timeout: 3  Parameters:    SomeVar:     Type: String     Description: My SomeVar     Default: default value  Resources:    HelloWorldFunction:     Type: AWS::Serverless::Function     Properties:       CodeUri: hello-world/       Handler: app.lambdaHandler       Runtime: nodejs12.x       Environment:         Variables:           SOME_VAR: !Ref SomeVar       Events:         HelloWorld:           Type: Api           Properties:             Path: /hello             Method: get  Outputs:    HelloWorldApi:     Description: "API Gateway endpoint URL for Prod stage for Hello World function"     Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"    HelloWorldFunction:     Description: "Hello World Lambda Function ARN"     Value: !GetAtt HelloWorldFunction.Arn    HelloWorldFunctionIamRole:     Description: "Implicit IAM Role created for Hello World function"     Value: !GetAtt HelloWorldFunctionRole.Arn 

from https://github.com/awslabs/aws-sam-cli/issues/1163#issuecomment-557874976

then in code

console.log(process.env.SOME_VAR); 

when you run sam local start-api and it will print default value

when you run sam local start-api --parameter-overrides SomeVar=other_value and it will print other_value

then if you create file env.json with this content

{ "PreviewsFunction": { "SOME_VAR": "123" } } 

when you run sam local start-api --env-vars env.json and it will print 123

p.s. it will work with start-api/start-lambda/invoke all in the same way, but it looks like sam deploy only works with --parameter-overrides SomeVar=other_value and no --env-vars