Bryce York Bryce York - 3 months ago 68
Node.js Question

Lambda can't keep up / dropping requests (via API Gateway) if more than 1 req per 30s (Process exited before completing request)

I'm running a relatively simple AWS Function to add a subscription to Stripe.

It runs fine unless I hit it shortly after I just hit it. Just trying to run it in PostMan one after the other fails and returns:

{"errorMessage": "Process exited before completing request"}


The requests are delivered via API Gateway.

Function is configured with 30s timeout and is take ~1300ms to run on the base 128M RAM (issue reproducible @ 256M).

I thought this was exactly what Lambda was designed to avoid... I'm second guessing my decision to use Lambda for a (synchronous) mission critical component.

EDIT: As requested, here's the function code:

var stripe = require('stripe');

exports.handler = function (event, context, callback) {
var self = this;
stripe = stripe(getKey(event.stage, 'STRIPE_SECRET_KEY'));
self.createSubscription = createSubscription;
self.validPayload = validPayload;

console.log('event: ', event);

if (self.validPayload(event, context)) {
self.createSubscription(event, stripe, callback, context);
}

/**
* checks that the necessary payload has been received
* if YES: returns true and allows process to continue
* if NO: throws context.fail with useful error message(s)
* operating under custom error code naming convention of
* http code + 3 digit ULM error code
* @param event - from Lambda
* @param context - from Lambda
* @returns {boolean} - whether the payload contains the required data
*/
function validPayload (event, context) {
var errorResponse = {
status: 400,
errors: []
};

if (!event.billing_email) {
errorResponse.errors.push({
code: 400001,
message: "No billing email provided."
})
}
if (!event.plan) {
errorResponse.errors.push({
code: 400002,
message: "No plan was selected."
})
}
if (!event.token) {
errorResponse.errors.push({
code: 400003,
message: "A valid credit card was not provided."
})
}

if (!!errorResponse.errors.length) {
context.fail(JSON.stringify(errorResponse));
return false;
} else {
return true;
}
}

/**
* Creates a new customer & subscription using stripe package method
* if success, executes callback with response data
* if fail, throws context.fail with useful error message(s)
* @param event - from Lambda
* @param stripe - probably not necessary...
* @param callback - from Lambda
* @param context - probably not necessary...
*/
function createSubscription (event, stripe, callback, context) {
stripe.customers.create({
source: event.token,
plan: event.plan,
email: event.billing_email
}, function (err, customer) {
if (err) {
var errorResponse = {
status: 400,
errors: []
};

errorResponse.errors.push({
code: 400004,
message: err.message
});

console.error('Customer/Plan Creation Failed');
callback(JSON.stringify(errorResponse));
} else {
callback(null, {
status: 200,
customer: customer
});
}
});

}

function getKey (stage, keyId) {
var keys = {
STRIPE_SECRET_KEY: {
staging: 'sk_test_123456',
prod: 'sk_live_123456'
}
};

if (stage === 'prod') {
return keys[keyId][stage];
} else {
return keys[keyId]['staging'];
}
}
};


EDIT 2: Dug into CloudWatch and found this error log:
TypeError: stripe is not a function at exports.handler (/var/task/exports.js:5:14)

Answer

@rowanu is correct, your problem is on this line stripe = stripe(getKey(event.stage, 'STRIPE_SECRET_KEY'));. Since the Lambda stays hot to handle subsequent requests any variables declared outside of the handler function will be seen by each new request that comes in. This should be a simple fix, don't redefine the stripe variable. Something like this would do the trick:

var stripe = require('stripe');
var stripeInstance; // undefined on startup

exports.handler = function (event, context, callback) {
  // now define stripeInstance if its not already defined
  if(!stripeInstance) {
    stripeInstance = stripe(getKey(event.stage, 'STRIPE_SECRET_KEY'));
  }
  // now all functions will be able to use the same instance of stripe. 
  // This assumes the event.stage is always the same, if you need a new instance for every request then remove the if statement
  // rename all references of stripe to stripeInstance
  ...
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