Malformed Lambda proxy response error in AWS occurs when we configure Amazon API Gateway proxy integration to work with an AWS Lambda function.

When we call the API, it will return a configuration error or a 502 status code.

Here, at Bobcares, we assist our customers with several AWS queries as part of our AWS Support Services.

Today, let us see how our support techs resolve this.

Malformed Lambda proxy response error in AWS

Most often, the source of these errors is the format of the Lambda function’s response.

In such a case, we come across a message similar to this in the logs:

Thu Oct 08 01:13:00 UTC 2016 : Execution failed due to configuration error: Malformed Lambda proxy response
Thu Oct 08 01:13:00 UTC 2016 : Method completed with status: 502

For API Gateway to handle a Lambda function’s response, the response must be JSON in this format:

{
"isBase64Encoded": true|false,
"statusCode": httpStatusCode,
"headers": { "headerName": "headerValue", ... },
"body": "..."
}

Moving ahead, let us see how our Support Techs resolve this.

First, we need to review the log output from the API Gateway console, or view the API Gateway log events in the Amazon CloudWatch console.

In the logs, we check the format of the Lambda function’s response to the API.

If it is not in JSON format, then we reformat it.

For example, here is a function in Node.js with the correct response format:

exports.handler = (event, context, callback) => {

var responseBody = {
"key3": "value3",
"key2": "value2",
"key1": "value1"
};

var response = {
"statusCode": 200,
"headers": {
"my_header": "my_value"
},
"body": JSON.stringify(responseBody),
"isBase64Encoded": false
};
callback(null, response);
};

In the result above, we can see four fields: statusCode, headers, body, and isBase64Encoded.

However, if the function is in another programming language, we need to refer to that language’s programming reference.

Then we have to confirm that the function returns a response in the correct format.

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Conclusion

In short, we saw how our Support Techs fix the Malformed Lambda proxy response error in AWS