Managing API Access to AI Services with Lambda Authorizers

Question

Pulumi · Accepted Answer

To manage API access to AI services with AWS Lambda authorizers, you'll need to create an API using Amazon API Gateway and then restrict access to the API by using a Lambda authorizer. A Lambda authorizer is a Lambda function that you provide to control access to your API Gateway API. This function returns an IAM policy that API Gateway uses to authorize or deny the API request.

Here's the process you'll follow in the code:
1. Define a Lambda function that will act as the authorizer. This function will inspect the incoming API calls and decide if they should be allowed or denied.
2. Create an API Gateway REST API resource.
3. Attach the authorizer to your API Gateway resources or methods that require authorization.
4. Export the API endpoint for later use or testing.

Below is a detailed Pulumi program in Python that demonstrates these steps:

```python
import pulumi
import pulumi_aws as aws

# Step 1: Define the Lambda function to be used as the authorizer
# This is a sample Lambda function. You would replace the code with your authorization logic.
# The function should return an IAM policy that grants or denies access.
lambda_authorizer_func = aws.lambda_.Function("lambdaAuthorizerFunc",
    runtime="python3.8",
    code=pulumi.AssetArchive({
        ".": pulumi.FileArchive("./authorizer"),  # Assuming you have your Lambda code in the 'authorizer' directory
    }),
    handler="authorizer.handler",  # The file 'authorizer.py' and 'handler' function inside it
    role=pulumi_aws.iam.Role("lambdaAuthorizerRole",  # IAM role with permissions needed by the Lambda function
        assume_role_policy="""{
            "Version": "2012-10-17",
            "Statement": [{
                "Action": "sts:AssumeRole",
                "Principal": {
                    "Service": "lambda.amazonaws.com"
                },
                "Effect": "Allow",
                "Sid": ""
            }]
        }""").id,
)

# Step 2: Create an API Gateway REST API
api_gateway = aws.apigateway.RestApi("apiGateway", description="API Gateway for AI Services")

# Step 3: Create an authorizer for API Gateway that invokes the Lambda function
authorizer = aws.apigateway.Authorizer("apiGatewayAuthorizer",
    rest_api=api_gateway.id,
    authorizer_uri=lambda_authorizer_func.invoke_arn.apply(lambda arn: f"arn:aws:apigateway:{aws.region}:lambda:path/2015-03-31/functions/{arn}/invocations"),
    authorizer_credentials=pulumi_aws.iam.Role("authorizerInvocationRole",  # IAM role that API Gateway uses to invoke the Lambda authorizer
        assume_role_policy="""{
            "Version": "2012-10-17",
            "Statement": [{
                "Action": "sts:AssumeRole",
                "Principal": {
                    "Service": "apigateway.amazonaws.com"
                },
                "Effect": "Allow",
                "Sid": ""
            }]
        }""").arn,
    type="TOKEN",  # TOKEN-based Lambda authorizer
    identity_source="method.request.header.Authorization",  # The header in the incoming request that contains the authorization token
)

# Step 4: Define a resource and method on the API Gateway that uses the Lambda authorizer for access control
resource = aws.apigateway.Resource("apiResource",
    rest_api=api_gateway.id,
    parent_id=api_gateway.root_resource_id,
    path_part="myservice",  # The URL path component for the service
)

method = aws.apigateway.Method("apiMethod",
    rest_api=api_gateway.id,
    resource_id=resource.id,
    http_method="GET",
    authorization="CUSTOM",
    authorizer_id=authorizer.id,
)

# Export the API endpoint for testing
pulumi.export("api_invoke_url", pulumi.Output.concat("https://", api_gateway.id, ".execute-api.", aws.region, ".amazonaws.com/", resource.path_part))
```

In this program, you should replace the Lambda code with your specific authorizer logic to make authorization decisions based on your requirements.

We use `pulumi_aws.lambda_.Function` to create a Lambda function which will act as an authorizer. The IAM role associated with this Lambda function (`lambdaAuthorizerRole`) needs permissions to be invoked and to perform necessary actions within your authorizer logic.

The authorizer is created with `pulumi_aws.apigateway.Authorizer`, specifying details such as the REST API ID, the URI of the Lambda function to be used, and the type of authorizer (which is set to "TOKEN" here).

After defining the API Gateway with `pulumi_aws.apigateway.RestApi`, we create a resource and method where we use the Lambda authorizer. The method is configured to require authorization via the custom authorizer defined earlier.

The `pulumi.export` call at the end outputs the URL of the deployed API Gateway so you can invoke and test the API.

Remember that you'll need to have your Lambda code for the authorizer ready in a directory named 'authorizer' and set appropriately in the `pulumi.AssetArchive`.

Replace the default policies given above with policies suitable for your own security requirements. The policies provided are fairly broad and intended for illustration purposes only.