Feature request: SAM local lambda server should support function ARNs on invoke API.

[bchampp]

Describe your idea/feature/enhancement

I wish that when running the sam local start-lambda server, I could hit my lambda functions by calling the invoke API with a function ARN instead of explicitly requiring a function name.

Proposal

Rather than explicitly requiring the lambda runner to take in the function name, it should take in either a function name or ARN, and normalize it somewhere around here

Things to consider:

1. Will this require any updates to the SAM Spec - No

[dcabib]

Hey @bchampp,

I'm a bit confused about what you're trying to achieve here. Let me explain why:

SAM already has sam remote invoke that does exactly what you'd need for calling deployed Lambdas with ARNs:

sam remote invoke arn:aws:lambda:us-east-1:123456789012:function:MyFunction

Now, if you add ARN support to sam local start-lambda, you realize it would still be calling your LOCAL function, right? It would just parse the ARN, extract "MyFunction", and run your local code. The region, account, everything else in that ARN - completely ignored.

So I'm not sure what problem this solves.

If you need to call deployed Lambdas → use sam remote invoke
If you need to test locally → use function names

What's the actual use case here that these don't cover?

Because adding ARN parsing just for the sake of it seems like unnecessary complexity. And it might actually confuse people into thinking they're testing against AWS when they're just running local code.

Can you explain what you're trying to do that doesn't work today?

[bchampp]

Hey @bchampp,

I'm a bit confused about what you're trying to achieve here. Let me explain why:

SAM already has sam remote invoke that does exactly what you'd need for calling deployed Lambdas with ARNs:

sam remote invoke arn:aws:lambda:us-east-1:123456789012:function:MyFunction
Now, if you add ARN support to sam local start-lambda, you realize it would still be calling your LOCAL function, right? It would just parse the ARN, extract "MyFunction", and run your local code. The region, account, everything else in that ARN - completely ignored.

So I'm not sure what problem this solves.

If you need to call deployed Lambdas → use sam remote invoke If you need to test locally → use function names

What's the actual use case here that these don't cover?

Because adding ARN parsing just for the sake of it seems like unnecessary complexity. And it might actually confuse people into thinking they're testing against AWS when they're just running local code.

Can you explain what you're trying to do that doesn't work today?

Yes -- the goal is to add the same flexibility for parsing function names in sam local as the actual lambda service has (which is covered through sam remote invoke).

Let's say I have an external system that invokes lambda functions using the full ARN. If I want to test against a sam local start-lambda server, my system will need to normalize the function ARNs. I think this should be handled by SAM local so it has parity with the actual lambda service.

Does that make sense?