How does AWS lambda get triggered by an api request? - amazon-web-services

Im assuming lambda is like the missing piece of the puzzle for a complete api request. So you create the apigateway and then write the lambda function which bridges the gap between taking a request and returning the output of the lambda function as the http response.
I've successfully followed guides on how to set up an API gateway that triggers AWS lambda to do something, but I still don't really understand what is being done.
How is the function def handler(event, context): being called by the aws apigateway? How does it get triggered and how is the output of handler sent back?

You do not need a Lambda "in the middle". Using Lambda Proxy integration in the API Gateway you can receive the full information about the request (endpoint URL, query parameters, etc) in your targeted Lambda event.
Have a look at the following Tutorial how to setup Lambda Proxy integration with API Gateway.
The tricky thing you should care about is the structure of the response that you will return from your lambda_handler. See the requirements here.
Answering the question of "how this happens"... In short, when an HTTP request comes to your API endpoint it is automatically routed to the mapped Lambda function. Behind the scenes a new container for the Function is spawned and your request comes to the event of the lambda_handler. API Gateway by default also creates a CloudFront distribution in front of itself to serve your requests more efficiently. Once your Lambda returns the response, API Gateway parses it and constructs the HTTP response out of it. The nice thing is that all of this is managed by AWS.

Related

How to trigger EventBridge with an HTTP request?

How do I create a rule that captures an HTTP GET that has some data and schedules the running of a lambda function at a specific time? I can write the lambda function but I am having trouble with creating an API endpoint to which I can send a "fetch" GET request. I tried creating an HTTP API in the API Gateway service. It returns this output:
{
"message": "Forbidden"
}
I am not much familiar with AWS. Please help me with creating a simple endpoint in AWS to which my app can send a GET request with some data, which will trigger an EventBridge rule to schedule the running of a lambda function at a specific time.
You don't need an API Gateway or a separate Lambda function.
To schedule the running of a specific Lambda function you can call the EventBridge put rule API.
You can find examples of the EventBridge user guide.

How to handle lambda retries invoked from api gateway?

The api gateway url is triggered/called by a form submit. Now, as this is a synchronous invocation, how do I handle a lambda retries and handle throttles?
Note: I am deploying api gateway along with lambda and use the url generated as webhook for form submit. So basically, it would be a one-way communication.
Flow:
form(payload)-> (api gateway)-> lambda-> lambda-> sqs-> lambda-> dynamoDb
There won't be an automatic Lambda retry when it's invoked from API Gateway afaik. If you are throttled or the request fails (perhaps because of a Lambda function error), your client is responsible for deciding how to recover and whether or not to retry, likely based on the HTTP response code.
Also worth reading:
A Detailed Overview of AWS API Gateway
How AWS Lambda Retry really works

How to create a usage plan for AWS HTTP API?

I am using AWS API Gateway with HTTP API which invokes a lambda function. However HTTP API doesn't include USAGE feature. According to my requirement I need to create a usage for a client depending on the status code of the response sent back by the lambda. Since I cant access the response sent by lambda in API Gateway, I am looking for an custom solution. I am planing to use STEP function.
For example:
Instead of API Gateway directly invoking a lambda function it can call a STEP function where I can execute LambdaA. next it would trigger LambdaB with response from LambdaA as input to LambdaB in a sequential manner. I don't know If this is the right approach
I would like to know what is best way of solving this problem...thanks in advance

Decision Making at API gateway Integration Request

I have a API gateway connected to SQS service, currently it just forward all the incoming requests bodies to SQS by SendMessage action.
I hope at integration request step I can check if the request has a certain field. If so, return a custom response and do not call the SQS service, otherwise forward the request body to SQS as I am doing right now.
I can do this by using a lambda function triggered by API gateway but i am wondering if I can do this without using lambda.
You may achieve that by setting up a request validator on AWS Api Gateway as explained here

Handing back a response to API Gateway from Lambda

I'm using API Gateway-to-Lambda for a few micro-services but in at least one case the service will take 20-30 seconds to complete so in cases like this I'd like to pass back an immediate response to the client, something like:
status: 200
message: {
progressId: 1234
}
and then allow the Lambda Function to continue on (and periodically updating the "processId" somewhere that is accessible to a client. The problem is that if you call context.succeed(), context.fail(), or context.done() that apparently stops the lambda function from further execution and yet it's the only way I know to flush the stdout buffer back to the API Gateway.
This has led me to a second approach which I haven't yet try to tackle (and for simplicity sake would love to avoid) which involves API Gateway calling a "Responder" Lambda function that then asynchronously fires off the Microservice and then immediately responds to the API Gateway.
I've tried to illustrate these two options in sketch format below. I'd love to hear how anyone's been able to solve this problem.
Currently API Gateway requires that the AWS Lambda integration is synchronous. If you desire asynchronous invocation of your Lambda function, you have 2 options:
Invoking the Lambda asynchrously, either with an AWS integration calling InvokeAsync on Lambda, or using an intermediate service such as SNS or Kinesis to trigger the Lambda function.
You're #2 diagram, using a synchronous Lambda invoke to initiate the asynchronous invoke.
As of Apr/2016 is it is possible to create async Lambda execution through API Gateway by using AWS Service Proxy. See http://docs.aws.amazon.com/apigateway/latest/developerguide/integrating-api-with-aws-services-lambda.html
You can send the X-Amz-Invocation-Type header, it supports async calls through the Event value
You can optionally request asynchronous execution by specifying Event as the InvocationType
http://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html#API_Invoke_RequestSyntax
Also, if you can't send it via your micro-service, you can configure this header to be passed by default through the Method Execution -> Integration Request -> HTTP Headers in your API Gateway Resource
This worked for me on a micro-service -> API Gateway -> Lambda scenario, like the mentioned on the question.