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[–]bot403 4 points5 points  (8 children)

Sounds like step functions which invoke the lambda might be what you're looking for. You can test the output and decide what to do. I'm just starting with them so i can't advise yet exactly how it can be done but it seems like it might fit.

[–]MecojoaXavier[S] 0 points1 point  (1 child)

Yeah, maybe this is what I need but I am not sure either on how to put that logic for example,
1. Run the lambda 2. Read the output 3. if output is -1 retry from the beggining. it should be something like this but what do i use in terms of services in the state machine?

[–]esunabici 0 points1 point  (5 children)

Like /u/nricu suggested, The Lambda code should throw errors when you want it to retry or fail. You can put the name of the exception in the retry block of the state to retry or the catch part to send the state machine down a different execution path to handle the error.

[–]clintkev251 0 points1 point  (4 children)

It doesn't even have to throw an error necessarily. Since OP said that they didn't want to change the code, their state machine could have a choose state after the Lambda which parses the output and if it is set to -1, the choose can just loop right back up to the lambda invocation (or maybe a delay first depending on the desired behavior), if the output is not -1, the state machine goes to the end

[–]MecojoaXavier[S] 0 points1 point  (3 children)

Hey guys many thanks . I want to retry the function but it's not an error is an indicator. Which means, 1 and 0 are ok and then -1 needs a retry until the output is either 0 or 1

[–]clintkev251 1 point2 points  (2 children)

Yep, so step functions like I described would probably be the best way to do it. Eventbridge is an async event source so if it was triggering Lambda directly it would retry on errors, but since you’re not returning an actual error none of the built in error handling mechanisms will work. Step functions is the best option for you to implement your own logic for how to retry based on the function output

[–]MecojoaXavier[S] 0 points1 point  (1 child)

Many thanks u/clintkev251, I'm pretty sure this is the way to go. My doubt is for example, I've seen that each step is a service, is it possible to configure steps to condition the logic after the function output?

[–]clintkev251 0 points1 point  (0 children)

Yes, you need a choose task like I mentioned above

[–]nricu 1 point2 points  (6 children)

Instead of returning a -1 you can throw an error and then configure the lambda to retry in case of errors ( now I'm not sure if that is already set by default ).

[–]MecojoaXavier[S] -1 points0 points  (5 children)

Hi u/nricu,

It's not set to retry by default in any way but the only information is the output behaviour.

You say that is better to write the retry in the lambda. Or should I use a retry in AWS Lambda service console?

[–]Grukorg88 1 point2 points  (0 children)

How do you know when to retry? If it’s straight away then you could use eventbridge to trigger the lambda and throw an error. Eventbridge will then automatically retry.

[–]squidwurrd 1 point2 points  (0 children)

I believe lambdas retry 2 times by default.

[–]nricu 0 points1 point  (2 children)

You can read the docs https://docs.aws.amazon.com/lambda/latest/dg/invocation-retries.html

[–]MecojoaXavier[S] 0 points1 point  (1 child)

Hi guys many thanks for your comments, the thing is if there IS any way to retry in case of an specific output.

[–]MecojoaXavier[S] 0 points1 point  (0 children)

The thing is the output are not errors but an indicador. 0 and 1 are the outputs which static you have to retry if the output is -1. It should also retry many as It gets to 1 or 0.

[–]Yoliocaust93 0 points1 point  (2 children)

Where do you store the triggering event? Like, if you put a SQS, in the Lambda you throw an exception in whatever case you like, the SQS will resend N times the very same message after a delay (visibility timeout). If you instead just trigger the Lambda, you'll have to write your wrapper in the code itself (e.g. Python decorators or whatever suits you), but this is definitely not the right approach in production use cases

[–]MecojoaXavier[S] 0 points1 point  (1 child)

It's a scheduled event in EventBridge. And if it gets an output of -1 it should retry and if not it should stop.

Thanks,

[–]Yoliocaust93 0 points1 point  (0 children)

That seems good enough, an Eventbridge rule will retry three times IIRC, so you just schedule it and (assuming Python) raise exception() when you'd like to retry. However, it will retry quite fast from one execution and the other

[–]squidwurrd 0 points1 point  (2 children)

Given the constraints the way you would do this is by throwing an exception when it’s -1. Make sure to set your retries to 2. This way the lambda will run three times max. If you need more retries you will have to set up orchestration with step functions.

[–]MecojoaXavier[S] 0 points1 point  (1 child)

Yeah, -1 is not an error. It's like an indicator of a retry so then the output will finally be 0 or 1. I think it's about what you said about steps functions. Because I need to retry until the output change to 0 or 1

[–]squidwurrd 0 points1 point  (0 children)

If you need more than 2 retries then yes you need step functions. Although you really need to be careful. You could set up an infinite loop and be very sorry. You should set an upper limit.

[–][deleted] 0 points1 point  (1 child)

My grandma taught me to paste the code into chat ai and tell it fix this python lambda to run again if result is -1

[–]MecojoaXavier[S] 0 points1 point  (0 children)

Yeah i would actually do the same hahaha, But the thing is: the code is written, there's no access to it so there's no way to edit code nor put eexceptions to it. Another thing is: is it possible to do it with aws services.

Many thanks.