lambda-lib

This library is a toolbox for creating AWS Lambda handlers that provides tooling and automation for:

• structured logging and serialization of both incoming events and responses;
• exception handling;
• remote calls to other lambda APIs (via HTTP, SNS or Kinesis), with automated -- Correlation id propagation -- Request and response logging -- AWS X-Ray instrumentation

Usage

Lambda Handler Builder

Supose you have a business logic module (myServiceModule in the example below) and must give an http endpoint to it, like so:

In such case, you might use LambdaEndpoint:

exports.myLambdaHandler = new LambdaEndpoint()
	.withHandler(myServiceModule.someBusinessHandler)
	.withStaticParams('myParam1', myParam2)
	.build();

This will return a lambda handler similar to the following:

exports.myLambdaHandler = async (event, context, callback) => {
	try {
		//... do some logging and event pre-processing
		let result = myServiceModule.someBusinessHandler('myParam2', myParam2);
		//... do some logging and success post-processing
		callback(null, result);
	} catch(e) {
		//... do some logging and error post-processing
		callback(errorResult);
	}
}

Lambda Handler Wrapper

An alternative way to achieve the same goal is to use the Labda Wrapper notation:

exports.myLambdaHandler = LambdaEndpoint.Wrap(async (event, context, callback) => {
		let myParam = event.queryStringParameters.myParam;
		return myServiceModule.someBusinessHandler('myParam2', myParam);
});

Using either Wrapper or Builder form, event will be pre-processed, so for instance, in the above example event.queryStringParameters will never be undefined.

Also, the error or success callback will be handled by the wrapper, all you have to do is return the data (or throw the proper exception).

Event parsing

Most of the times, you may not have static parameters to your inner service call. You may get such values from the incoming event like such:

exports.myLambdaHandler = new LambdaEndpoint()
	.withHandler(myServiceModule.someBusinessHandler)
	.withEventParams(e => [e.body.some, e.queryStringParams.someOther])
	.build();

This would be similar to:

exports.myLambdaHandler = async (event, context, callback) => {
	try {
		let param1 = JSON.parse(event.body).some;
		let param2 = event.querystringParams.someOther
		let result = myServiceModule.someBusinessHandler(param1, param2);
		callback(null, result);
	} catch(e) {
		//...
	}
}

Note that event.body is automatically parsed, but only if it's headers include content-type=application/json

Error handling

Handled Business Exceptions

TODO

Unhandled Business Exception

TODO

Provided Clients: cascading function calls

Now let's assume your lambda or business logic may need to access some other lambda. Using the provided clients ensures these calls will be logged in a standard and structured manner, and that will propagate logging settings and correlation id's.

• HTTP

const { httpClient, RemoteException } = require('@buildist/lambda-lib').Clients;

try {
	let response = await httpClient.makeRequest('GET', 'https://my.service/foo');
} catch(e) {
	if(e instanceof RemoteException) {
		let {statusCode, errorCode, message} = e;
	}
}

• SNS

//TODO

• Kinesis

//TODO

Log

You must set the log level in lambda's environment variable process.env.LOG_LEVEL, and it must be either DEBUG, INFO, WARN or ERROR. The default value is DEBUG.

Using the service builder and client libraries, it will be automatically logged:

• ERROR
  • Errors with attached invocation event)
• INFO
  • Incoming Events
  • Outgoing service responses (callback)
• DEBUG
  • Outgoing HTTP, SNS and Kinesis events
  • Incoming HTTP responses

//example log output for the cascading function calls scenario: 
{"message":"LAMBDA EVENT RECEIVED","level":"INFO","awsRegion":"us-west-2","awsRequestId":"myAwsRequestId","x-correlation-id":"myAwsRequestId","Debug-Log-Enabled":"true","httpMethod":"GET","headers":{}}
{"message":"HTTP REQUEST","level":"DEBUG","awsRegion":"us-west-2","x-correlation-id":"myAwsRequestId","x-correlation-myKey":"myVal","hostname":"my.host","path":"/foo","port":null,"method":"GET","headers":{"x-correlation-id":"myCorrelationId","x-correlation-myKey":"myVal"}}
{"message":"HTTP RESPONSE","level":"DEBUG","awsRegion":"us-west-2","x-correlation-id":"myAwsRequestId","x-correlation-myKey":"myVal","statusCode":200,"body":"{}","headers":{"content-type":"application/json"}}
{"message":"LAMBDA RESPONSE","level":"INFO","awsRegion":"us-west-2","awsRequestId":"myAwsRequestId","x-correlation-id":"myAwsRequestId","Debug-Log-Enabled":"true","statusCode":200,"headers":{"Content-Type":"application/json","Access-Control-Allow-Credentials":true}}

Correlation IDs

If the remote lambda is build using this lambda-builder, they will log the same correlation ID in the incoming event, and you will be able to track a long-living business event in the logs of every function involved.