samconfig.toml env_vars are overridden by launch.json

Describe the bug

When the extension is used to launch a SAM Lambda function using a launch.json configuration, environment variables for the Lambda function are overridden even if env_vars is configured in samconfig.toml.

Workarounds

• Run the SAM commands manually, bypassing the toolkit. Environment variables configured in samconfig.toml are passed to Lambda as expected. This workaround gives up the ability to debug since we’re not using the toolkit.

  sam build --template Template.yaml --use-container
  # --config-file is required when samconfig.toml is not within the same directory as template.yaml
  sam local invoke MyFunction -t .aws-sam/build/template.yaml --config-file ../../samconfig.toml
  

• Configure environmentVariables within launch.json instead of samconfig.toml. This is per-function and also VS Code-specific.

To Reproduce

1. Create .vscode/launch.json:

{
    "configurations": [
        {
            "type": "aws-sam",
            "request": "direct-invoke",
            "name": "project:MyFunction",
            "invokeTarget": {
                "target": "template",
                "templatePath": "${workspaceFolder}/Template.yaml",
                "logicalId": "MyFunction"
            },
            "lambda": {
                "payload": {},
            },
            "sam": {
                "localArguments": ["--config-file", "${workspaceFolder}/samconfig.toml"],
            }
        }
    ]
}

1. Create samconfig.toml

version = 0.1

[default.build.parameters]
# use_container required to avoid spurious errors such as
# Error: PythonPipBuilder:ResolveDependencies - list index out of range
use_container = "true"

[default.local_invoke.parameters]
# env_vars required to pass environment variables to the
# Lambda function image container when debugging locally.
env_vars = "env-vars.json"

1. Create env-vars.json

{
    "Parameters": {
        "S3_ENDPOINT_URL": "http://localstack:4566",
        "SNS_ENDPOINT_URL": "http://localstack:4566",
        "DYNAMODB_ENDPOINT": "http://localstack:4566"
    }
}

Behaviour using Toolkit

$:~/repositories/project$ cat /tmp/aws-toolkit-vscode/vsctkG3cdmX/env-vars.json 
{"MyFunction":{}}

print(os.environ.get('S3_ENDPOINT_URL'))
''

Behaviour using SAM CLI directly

print(os.environ.get('S3_ENDPOINT_URL'))
'http://localstack:4566'

Expected behavior

The Toolkit should not override environment variables set by samconfig.toml.

Desktop

• OS: Linux x64 5.4.72-microsoft-standard-WSL2
• Visual Studio Code Version: 1.59.0
• AWS Toolkit Version: 1.28.0

[justinmk3]

AWS Toolkit 1.29 includes a fix for this. @danw-mpl thank you for your helpful analysis!

[danw-mpl]

Almost correct. I’m sure the “merge” behaviour could remain as-is. Just don’t send --env-vars when environmentVariables isn’t present. This would mean we can use configuration from samconfig.toml.