AWS Application Load Balancer 无法处理内容编码为 gzip 且内容类型为 application/json 的请求正文

Question

I am trying to send a gzipped json as POST request body to AWS Application Load Balancer, which calls AWS Lambda.

When I set the content type request header as application/json, I get 502 Bad Gateway error as response and AWS Lambda does not get invoked.

I am using following curl command.

curl -v -s --data-binary @samples/small-batch.json.gz -H "Content-Encoding: gzip" -H "Content-Type: application/json" -X POST https://sub.domain.com/batch

Am I sending invalid request headers?

My AWS Lambda code:

import json

def lambda_handler(event, context):
    print("event = ", event)
    return {
            'statusCode': 200,
            'body': json.dumps({ 'success': True }),
            'headers': {
                'Content-Type': 'application/json'
            }
        }

Update

If I place request with empty content type, then Lambda gets called successfully.

curl -v --data-binary @samples/small-batch.json.gz -H "Content-Type: " -H "Content-encoding: gzip" -X POST https://sub.domain.com/batch

If I make request with application/gzip content type then Lambda gets called successfully.

curl -v --data-binary @samples/small-batch.json.gz -H "Content-Type: application/gzip" -H "Content-encoding: gzip" -X POST https://sub.domain.com/batch

The 502 error is occurred only when I request with Content Encoding as gzip and Content Type as application/json . But as per my understanding these are valid headers.

Update 2

From the documentation I found at https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html

If the content type is one of the following types, the load balancer sends the body to the Lambda function as is and sets isBase64Encoded to false: text/*, application/json, application/javascript, and application/xml. For all other types, the load balancer Base64 encodes the body and sets isBase64Encoded to true.

I think because of this, header Content-Encoding: gzip can not be coupled with header Content-Type: application/json . I think something is going wrong in ALB while calling Lambda.

Answer 1

It's probably not a problem with header Content-Encoding: gzip & Content-Type: application/json but it could be a problem with the binary data size (which could be more than 1 MB) that you are sending.

According to AWS documenation, Lambda has limitation in request and response payload while using with ALB.

• The maximum size of the request body that you can send to a Lambda function is 1 MB.

• The maximum size of the response JSON that the Lambda function can send is 1 MB.

Please refere: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html