Call AWS Lambda from a Lambda using NodeJS with Headers and Path

Question

I'd like a lambda called GoalsFeed to invoke another lambda called Goals using AWS.Lambda. This seems to work, except for two things:

I'm not sure how to pass a header through to the target service.
The FunctionName is "myapp-goals-get" (aka Goals) but I want to go to a specific path on that service - the three paths shown below are all valid, but i'm wanting to specify the "../owner/123" path.

http://aws.com/myapp/goals

http://aws.com/myapp/goals/1

http://aws.com/myapp/goals/owner/123

Below is my first crack at this, can someone help me modify this to pass "tenantid" as a header and to ensure that when "myapp-goals-get" is invoked, it sees itself as being invoked from the path with "../owner/123" ?

// fetch back all goals by userid
var lambda = new AWS.Lambda({
    region: 'us-east-1' 
});

var payload = {};
payload[ "userId" ] = "123";
payload[ "tenantid" ] = "1";

const params = {
  FunctionName: 'myapp-goals-get',
  InvocationType: "RequestResponse",
  Payload: JSON.stringify(payload)
};

lambda.invoke( params, function(error, data) {
  console.log( "data: %s", JSON.stringify( data ) );

  if( error ) {
    context.done( 'error', error );
  } 
  else if( data.Payload )
  {
    context.succeed( data.Payload )
  }
});

Stop and think about this for second. When you invoke a Lambda function using lambda.invoke() there are no HTTP elements in the request -- you are instructing the Lambda API to invoke the the function directly, with your Payload -- and there can be nothing else in that request. There are really no headers, no path, just the incoming event structure, which here you are populating with the stringified contents of payload. Any sense of "headers" or "paths" on the other side depends entirely on how that other function interprets its incoming event object. Show code please. — Michael - sqlbot
– Michael - sqlbot, Commented Mar 28, 2018 at 3:36

John · Accepted Answer · 2018-03-28 01:11:07Z

1

The proper way to handle this use-case is to setup a REST API with API-Gateway + Lambda using proxy integration ( to forward all HTTP Headers/body/etc to your lambda function )

https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-create-api-as-simple-proxy-for-lambda.html#api-gateway-proxy-integration-lambda-function-nodejs

You can then chain inside the same request or make another call to your API.

answered Mar 28, 2018 at 1:11

John

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3 Comments

Michael - sqlbot Over a year ago

That seems to add unnecessary complexity, latency, and cost, compared to just invoking the second function, directly.

John Over a year ago

@Michael-sqlbot I beg to differ, lambda functions are invoked by events, and if wanting to process incoming HTTP data, then HTTP call triggering the functions seems like the natural course of action, and the resources API-GW + Lambda Proxy integration are purpose build for that. If it's as simple as needing to pass data to another function call VS just handling in the same process, just save the data and recall on a subsequent call.

Michael - sqlbot Over a year ago

OP is already in a Lambda function, wanting to invoke a second Lambda function from there. The choices are (a) make an API call to the Lambda service to invoke the second function, or (b) make an HTTP request to API Gateway so that API Gateway can do... exactly the same thing -- make an API call to the Lambda service to invoke the second function. You are adding extra milliseconds, additional complexity, and an entirely avoidable cost increase of $3.50 per million requests, with no apparent benefit.

Lypheus · Accepted Answer · 2018-03-30 06:25:29Z

1

My solution was to simply reset the pathParameters and pass the Event through to the child lambda.

event.pathParameters = { };
event.pathParameters.id = 123;
const tdParms = { 
    FunctionName : 'mylambda', 
    Payload: JSON.stringify( event ) 
};

lambda.invoke( tdParms, function( error, data ) {  
    ... 
}

answered Mar 30, 2018 at 6:25

Lypheus

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