Make the failure as Lambda result with HTTP status code 4xx, 5xx #643

mirumirumi · 2023-04-18T01:56:18Z

mirumirumi
Apr 18, 2023

I'm creating an HTTP response using the following code:

use lambda_http::{Body, Error, Response};

fn base_response_builder() -> http::response::Builder {
    Response::builder().header("Content-Type", "application/json")
}

pub fn ok(body: impl Into<Body>) -> Result<Response<Body>, Error> {
    Ok(base_response_builder().status(200).body(body.into())?)
}

I've also created this for 4xx and 5xx status codes, but since it ultimately returns an Ok from Lambda, the execution result of Lambda is considered "successful" rather than "failed". I would like the Lambda result to be treated as a failure when it's not a 2xx status code, so I want to return an Err at the end while setting the status code.

(My understanding is that if the Lambda Function returns Ok(), it is considered "success" and if it returns Err(), it is considered "failure", is that correct?)

How can I achieve this scenario?

greenwoodcm · 2023-04-18T16:16:06Z

greenwoodcm
Apr 18, 2023
Maintainer

You likely want to leave the function's return value as Ok(_). When you return an Err(_) to the runtime it will signal a failure back to the Lambda service, which tells the service that the execution environment has crashed or is otherwise bad. That means that Lambda will restart the execution environment before issuing another invoke. In most cases like you're describing, the code ran successfully, it just wants to signal an error from a downstream dependency or a logical error or something to the caller. In such cases, you likely want the app to keep running and keep responding to subsequent requests - it was the request that failed, not the whole app.

So you should consider whether the entire application has now failed (thus return an Err), or if the single request failed and the app should keep running (thus return an Ok). Does this help?

1 reply

mirumirumi Apr 19, 2023
Author

@greenwoodcm
I see.
I understand that it is a very bad idea to treat Lambda itself as a "failure", at least in 4xx series errors.

For actual server-related failures that occur, such as AWS SDK errors, "failure" might be fine, but even if it doesn't explicitly return a status code, API GW will return 502 if the execution result is a failure (which can be mapped to 500), and it's already good enough to be I noticed that.

Thanks!

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Make the failure as Lambda result with HTTP status code 4xx, 5xx #643

{{title}}

Replies: 1 comment 1 reply

{{title}}

{{title}}

Select a reply

Make the failure as Lambda result with HTTP status code 4xx, 5xx #643

mirumirumi Apr 18, 2023

Replies: 1 comment · 1 reply

greenwoodcm Apr 18, 2023 Maintainer

mirumirumi Apr 19, 2023 Author

mirumirumi
Apr 18, 2023

Replies: 1 comment 1 reply

greenwoodcm
Apr 18, 2023
Maintainer

mirumirumi Apr 19, 2023
Author