AWS API Gateway integration request Http headers not being passed to lambda - amazon-web-services

Question

This is similar to this post API-Gateway Integration Request HTTP Header not mapping query string to header but I can't see any answer for it and all of the answers are not related to what the question is intended.
I am trying to add the integration request parameters in API Gateway, but whenever I set 'Http Headers' as shown here and 'Mapping template' as passthrough, I could not see that header when I log inside the lambda.
Also in the integration response I cannot reference it inside the integration header response parameters. The "integration.response.header.cokers" will be returned blank when I invoke the API. This is how I configured the integration response

Answer 1

Ultimately the solution here is to implement a lambda proxy integration.
A proxy integration in API Gateway tells API Gateway to simply forward all headers to the integration for processing, which means you will see all of those values in your lambda function.
NOTE: Lambda has to return a specific response format back to API Gateway if it's a proxy integration. Ultimately, the response should be something like:
{
'statusCode': 200,
'headers': {
'echo-proxy': True
},
'body': 'some payload'
}
What you are trying to do right now is map everything manually, which is a deprecated approach and usually you don't want to do that unless you absolutely have to because it's kind of a pain.
If you have to map the headers manually start by mapping them in the the method request so it can carry on to the next step and so on. Basically like this:
Method Request -> Maps variable to Integration Request -> Maps variable to Body Mapping Template -> Maps variable to actual request header
What you have in your screenshot for the Integration Request -> HTTP Headers is:
Name: cokers
Mapped from: 'blah'
However, "mapped from" should look something like "method.request.header.coker" which is a standardized path (meaning to get the value from the Method Request Header field with name "coker").
Once you have added the coker header to the Method Request, and the Integration Request HTTP Headers are mapped correctly, you have to implement a mapping template. Set the content-type to application/json with passthrough set to "When there are no templates defined(recommended)" and a simple mapping template:
{
"headers": {
"coker" : "$input.params('coker')"
}
}
That is the way my API is setup and it returns the following to me because I had my lambda function return the event as a json object back to API GW:
{"body": "{\"headers\": {\"coker\": \"mapped\"}}", "statusCode": 200}
NOTE: the value of my header "coker" in the request on the client side is "mapped"
UPDATED ANSWER
To map the original "coker" header to "coker2" (or any other name you want to give it) you simply set the name of the header in your mapping template like so:
{
"headers": {
"coker2" : "$input.params('coker')"
}
}
Then edit your lambda function to return "coker2" header and you should get a response like this:
{"body": "{\"headers\": {\"coker2\": \"mapped\"}}", "statusCode": 200}