Share code between AWS lambda functions in node.js

Question

It seems it is not possible to pass around some code (containing data and functions) that is invoked as a AWS lambda function within another AWS lambda function.

For example, take this customConfigLambda:

var callbackPayload = {};

callbackPayload.fooData = 'fooFromData';
callbackPayload.fooFunction = function() {return 'fooFromFunction'; };

exports.handler = (event, context, callback) => {
    callback(null, callbackPayload);
};

When I call the previous AWS lambda function in another AWS lambda function like here:

var AWS = require('aws-sdk');
AWS.config.update({accessKey: '123', secretAccessKey: 'abc', region: 'us-east-1' });
var lambda = new AWS.Lambda({region: 'us-east-1'});

exports.handler = (event, context, callback) => {
    var params = {FunctionName: 'customConfigLambda'};
    lambda.invoke(params, function(err, callbackPayload) {
        if (err) {
            // do nothing
        }
        else {
            console.log('callbackPayload:', JSON.stringify(callbackPayload, null, 2));
        }
    });
};

Then I can see only callbackPayload.fooData but not callbackPayload.fooFunction.

How can I have some callbackPayload.fooFunction(s) shared between multiple other AWS lambda functions?

Jghorton14 · Accepted Answer · 2019-01-09 13:57:26Z

2

As of AWS Reinvent 2018, Amazon has introduced Lambda Layers.

Lambda Layers, a way to centrally manage code and data that is shared across multiple functions.

The idea is that now you can put common components in a ZIP file and upload it as a Lambda Layer. Your function code doesn’t need to be changed and can reference the libraries in the layer as it would normally do instead of packaging them separately.

answered Jan 9, 2019 at 13:57

Jghorton14

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rsp · Accepted Answer · 2016-06-21 12:21:36Z

1

See the docs on Using the Callback Parameter at:

http://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html#nodejs-prog-model-handler-callback

It says this about the result (the callbackPayload in your code):

result – is an optional parameter that you can use to provide the result of a successful function execution. The result provided must be JSON.stringify compatible. If an error is provided, this parameter is ignored.

To be JSON.stringify compatible you cannot have any functions there. See the http://json.org/ to see what is valid JSON (only strings, numbers, objects, arrays, true, false and null).

If you want to share code between your AWS Lambda functions in a broad sense, you have to require the same Node module in both of them, so that you can make a common set of functions available to all of your AWS Lamda handlers. But you cannot pass around arbitrary code between them because those will not survive the JSON.stringify.

As a test you can try running this in the browser:

var callbackPayload = {};

callbackPayload.fooData = 'fooFromData';
callbackPayload.fooFunction = function() {return 'fooFromFunction'; };

alert(JSON.stringify(callbackPayload));

(see DEMO) or this in Node:

var callbackPayload = {};

callbackPayload.fooData = 'fooFromData';
callbackPayload.fooFunction = function() {return 'fooFromFunction'; };

console.log(JSON.stringify(callbackPayload));

and see the result:

{"fooData":"fooFromData"}

The functions is stripped out during the serialization process.

Of course you could do something like this:

callbackPayload.fooFunction
    = function() {return 'fooFromFunction'; }.toString();

and get a JSON result:

{"fooData":"fooFromData","fooFunction":"function () {return 'fooFromFunction'; }"}

which you could theoretically eval on the other end but I wouldn't really recommend it.

edited Jun 21, 2016 at 12:21

answered Jun 21, 2016 at 12:08

rsp

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3 Comments

TPPZ Over a year ago

Thanks, I was hoping there was a way :) Regarding requireing custom modules in different lambda functions is there a way that involves plain code (i.e. no ZIP/S3 files uploaded)? Regarding eval I guess that works neat only when functions don't have input parameters?

rsp Over a year ago

@TPPZ You may take a look at the Serverless project (formerly known as JAWS) - see this info: docs.serverless.com/docs/installing-serverless It may help you a lot with deploying many functions that share some common code base. As for evaling the functions, you could eval a string "function (x) {return x; }" and the result of eval would be a function that you could run with a parameter. I don't recommend it because it gets messy - the symbols inside the function don't get access to the original scope where it was written but the scope of where it was evaled, for example.

TPPZ Over a year ago

Ok thanks for the link and the details. For the sake of completeness, one could do: var fooFunctionParsed = eval('(' + callbackPayload.fooFunction + ')'); then use it like const inputX = 42; const outputX = fooFunctionParsed(inputX);. I did not investigate that much about scopes like this, but for simple helper/cosmetics functions, that return a combination of the input parameters, eval seems the quickest solution.

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