Get IP address of function caller

[johndevs]

How can I get the IP address of a function caller? Is there any way of getting the original HTTP request?

[denismakogon]

Hi! There’s no IP address of a function. The only endpoint you have is the Fn server IP address.

Would you mind to elaborate when and when you’d like to get the original request?

I suppose you’d like to get the request inside of function. I assume you use an FDK, in order to get the request you need to use the context (the way it works depends on an FDK and programming language).

[zootalures]

Assuming this is for HTTP triggers does it suffice for the the trigger handler to add X-Forwarded-For at the gateway?

[johndevs]

I'm using the Java FDK, but I guess this is a generic issue for all the FDKs to be able to resolve the details of the incoming request.

The use-case I'm trying to implement is to implement an analytics end-point as a FN function where some details of the caller are stored. The IP address is one of those details.

For the caller IP use-case the X-Forwarded-For header is fine, but the optimal implementation from my point-of-view would be that the (Java) FDK would provide a injected type RequestEvent (or similar) that would contain the details of the original request. For other FDK's a similar thing can probably be done as well.

[denismakogon]

Hi! So, in this case I’d recommend to add a requirement to you application - force a caller to tell who is he, i.e. force them to set a header X-Whoami or X-Caller-Id. There are plenty of way to make it work.

FDKs provide you whatever is sent by a caller of a function. Meaning if the info is not there - it wasn’t sent by a caller.

[johndevs]

@denismakogon Sure, I can manually do it but then I have to trust what the clients are sending to the function. That is not really an option.

What I am after is something I can currently can do with AWS API Gateway (https://aws.amazon.com/premiumsupport/knowledge-center/custom-headers-api-gateway-lambda/) allowing access to the original request and mapping it onto JSON.

For example via the API gateway I can do something like this:

#if($context.identity.sourceIp == "123.45.55.43")
  {
    "source_ip": "$context.identity.sourceIp"
  }
#else
  $broken
#end

This allows me to implement IP filtering, logging, etc.