Is async recommended?

[winzig]

I've seen function handlers specified like this in your samples:

public string Handler(S3Event s3Event)

And also like this from the AWS Toolkit for VS/Lambda support:

public async Task Handler(S3Event input, ILambdaContext context)

Is there documentation anywhere on best practices?

[normj]

It just depends what your function is doing. If you function is calling async methods, like calling async methods on the AWS SDK for .NET, then you should have your function being async. If your function isn't making any async methods then there is no reason to make your function be async.

[winzig]

Oh, duh, sorry! 😁 I just spent a few weeks working on a Node.js-based Lamda function, everything is asynchronous and waterfalls, and was thinking the use of async here had some special meaning related to the Lambda execution environment.

[mid787]

@normj It's also related to money. If you function support async and you wait() or .Result it , you're actually holding a thread consuming CPU cycles which ,in large scale , costs more. Right ?

[Kralizek]

Imho it's irrelevant because you get billed by the amount of time the container hosting the lambda function is up, not by how much CPU you are actually using.

[mid787]

@Kralizek https://read.acloud.guru/save-time-and-money-with-aws-lambda-using-asynchronous-programming-3548ea65f751

One of the easiest ways to tighten your Lambda bill is to not pay for waiting — which means getting your arms around async. Paying for idle is bad.

[Kralizek]

@RoyiNamir as I read the article, it says that you either decompose the lambda in multiple ones and let AWS invoke the next step, or you use language constructs to parallelise your work until you actually need the result (hence shortening the execution of the lambda).

In .NET lingo, you could do something like

var task1 = DoSomethingAsync();
var task2 = DoSomethingElseAsync();
var task3 = DoYetAnotherThingAsync();

await Task.WhenAll(task1, task2, task3);

as opposed to

await DoSomethingAsync();
await DoSomethingElseAsync();
await DoYetAnotherThingAsync();

[mid787]

@Kralizek thanks for clarification