Error when trying to use lambda to return client IP

Question

Hello. Attempting to create something similar to http://checkip.amazonaws.com/ .
Am open to other solutions, but the one I found is https://stackoverflow.com/questions/33062097/how-can-i-retrieve-a-users-public-ip-address-via-amazon-api-gateway-lambda-n .

When I use this for the lambda function -

'use strict';
console.log('Loading function');
exports.handler = (event, context, callback) => {
    console.log('SourceIP =', event.identity.sourceIP);
    callback(null, event.identity.sourceIP);
};

and this for the mapping template -

{
    "sourceIP" : "$context.identity.sourceIp"
}

I get this error -

{
    "errorType": "TypeError",
    "errorMessage": "Cannot read property 'sourceIP' of undefined",
    "trace": [
        "TypeError: Cannot read property 'sourceIP' of undefined",
        "    at Runtime.exports.handler (/var/task/index.js:4:46)",
        "    at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"
    ]
}

Can someone please walk me through the steps to correctly implement the lambda function and mapping template above or perhaps if you have a better method to return the client IP of a simple get request, please share?

Thank you

Accepted Answer

It depends on which API you are using. If you are using HTTP API, the source IP is at `event.requestContext.http.sourceIP` or event.headers.x-forwarded-for. If you are using REST API it will be in `event.headers.X-Forwarded-For` or `event.requestContext.identity.sourceIp`. You are trying to access `event.identity.sourceIP`.

Note, in both cases you do not need a mapping template, just return a body from the Lambda function. If you are using REST API, you may be able to implement it using a Mock integration and a mapping template, although I did not test it.

Error when trying to use lambda to return client IP

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