AWS Lambda - Controlling the application flow

Question

I am trying to properly structure my AWS lambda. I am attempting to exit the Lambda when I encounter an error. With the simple one function Lambda, I do this:

exports.handler = async (event, context) => {    
    const someError = new Error('Something is wrong');
    throw someError;
};

It ends up in DeadQueue as expected (after several tries).

When I want to resolve it with success, I do this:

exports.handler = async (event, context) => {  
    // ... some code here        
    return {};    
};

Now I want to structure my application using requires, so I have something like this:

//Main execution point
const validator = require('./Validate/Validator');

exports.handler = async (event, context) => {    
    let aaa = validator.validate(operationName);
    console.log('I should not bere here')        
};

And the validator itself:

exports.validate = async (schemaName, payload) => {
    console.log('I am coming here')
    try {            
        const Schema = require(`../ValidationSchemas/${schemaName}`).schema;
    }
    catch (e) {            
        const schemaError = new Error('Validation schema not found. Operation does not exist.');
        throw schemaError;
        //process.exit(0);            
    }
};

What happens in validator, if I throw an error, error is thrown, but my execution is continued in the main (caller) lambda function. I thought to stop it there using

process.exit(0)

It does work. Lambda is terminated. But it looks like a bad approach for some reason. Ideally I would do it from the main function, but I am thinking about the best approach.

A.Khan · Accepted Answer · 2019-02-08 10:08:15Z

1

You need to implement error handling in Lambda function.

const validator = require('./Validate/Validator');

exports.handler = (event) => {

  try {
    let aaa = validator.validate(operationName);
  }
  catch (error) {
    return error;
  }  

};

answered Feb 8, 2019 at 10:08

A.Khan

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5 Comments

Amiga500 Over a year ago

If I understand correctly, I should handle all errors in my execution function?

Amiga500 Over a year ago

It works. Based on your suggestion, I control the flow inside the main function. Side question. Is it ok (in Lambda) context to use this: process.exit(0)?

A.Khan Over a year ago

it depends on your use case why would you want to use process.exit. It would just terminate the container execution.

Amiga500 Over a year ago

At the end using it, has same side effect like throwing an error? In terms, that it ends up in the DeadSQS?

Michael - sqlbot Over a year ago

@VedranMaricevic it should have the same ultimate effect but it's almost certainly going to come with a future performance penalty, because the process -- and possibly the container -- can't be reused. The process will need to be respawned or the container will need to be replaced, by the service, either of which can reasonably be expected to cause a future invocation of the function to incur some amount of unnecessary startup latency.

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