Lambda function as image, how to find your handler URI

Question

Hello,

I have followed all of the tutorials on how to build an AWS Lambda function as a container image.  I am also using the AWS SAM SDK as well.  What I don't understand is how do I figure out my end-point URL mapping from within my image to the Lambda function?

For example in my docker image that I am using the AWS Python 3.9 image where I install some other packages and my python requirements and my handler is defined as:

summarizer_function_lambda.postHandler

My python file being copied into the image is the same name as above but without the .postHandler

My AWS SAM Template has:

AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31
Description: AWS Lambda dist-bart-summarizer function

# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
  Function:
    Timeout: 3

Resources:
  DistBartSum:
    Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
    Properties:
      FunctionName:  DistBartSum
      ImageUri: 
      PackageType: Image
      Events:
        SummarizerFunction:
          Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
          Properties:
            Path: /postHandler
            Method: POST

So what is my actual URI path to do my POST call either locally or once deployed on Lambda??

When I try and do a CURL command I get an 
"{"message": "Internal server error"}% "

curl -XPOST "https:///Prod/postHandler/" -d '{"content": "Test data.
"}'

So I guess my question is how do you "map" your handler definitions from within a container all the way to the end point URI?

Answer

The url you are creating looks correct. You can reference the [API Gateway tutorial](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-create-api-as-simple-proxy-for-lambda.html) and see that they have a section showing how to build the URL:

```
To test the deployed API using cURL:
1. Open a terminal window.
2. Copy the following cURL command and paste it into the terminal window, replacing *r275xc9bmd* with your API's API ID and *us-east-1* with the region where your API is deployed.

curl -v -X POST \
  'https://r275xc9bmd.execute-api.us-east-1.amazonaws.com/test/helloworld?name=John&city=Seattle' \
  -H 'content-type: application/json' \
  -H 'day: Thursday' \
  -d '{ "time": "evening" }'
```

Based on what you provided, it looks like API Gateway's Stage name is "Prod" so I would expect the following to work after replacing *r275xc9bmd* with your API's API ID and *us-east-1* with the region:
```
curl -v -X POST \
  'https://r275xc9bmd.execute-api.us-east-1.amazonaws.com/Prod/postHandler' \
  -H 'content-type: application/json' \
  -d '{ "content": "Test data.
" }'
```

You might want to confirm API Gateway and Lambda is configured correctly and look at the CloudWatch logs to find the error.

Answer

When you create a Lambda function, regardless if using the zip file format or the container image format, the function should have a Lambda handler. The handler is the entry point to your function. 
This is where you write your business logic. If you are using Python, it would look like:

```
def handler(event, context):
    print (event)

return {
        'statusCode': 200
    }
```

In your case it seems that you configured the handler to be `summarizer_function_lambda.postHandler` which means that the handler is in a file named `summarizer_function_lambda` and the method is named `postHandler`.

If you want to invoke your function using a URL you have two options: 1. Create an API in API Gateway and set the integration to be the Lambda function. or 2. Create a Lambda function URL. Looking at your template you are using the first option which also creates an API. To find the URL for that API you can either include it in the Outputs section of the template, or go to the CloudFormation console, and check the resources that were created in your stack. API Gateway should be in there.

Lambda function as image, how to find your handler URI

More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst

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