How to throw exceptions from AWS lambdas but not trigger AWS cloudwatch? - amazon-web-services

Question

So I have the following scenario.
We have a specific set of custom exceptions that we need to throw from the backend (written with AWS Lambdas) so that the frontend can receive a specific response that he knows how to treat.
Our responses for the client (frontend) look like this in case of an error.
We have code, statusCode, message
{
"error": {
"code": 4004,
"statusCode": 404,
"message": "Not found"
}
}
Now, the issue is that the way we do it is by extending the Exception class in Python, so when something happens we can do raise CustomException.
It's all working fine, the only issue that we have is that AWS Cloudwatch treats this as ERRORS and so we are in a case where every single BadRequest is costing us an error in cloudwatch, which is something we do not want.
I would like to build it in such a way that I manage to throw this response to the client but the status of the HTTP request to be the actual statusCode that I put. So far, I have only managed to do something like this:
As you can see, I have the response I need, however, the statusCode for the HTTP request is 200, when in fact it should be 404.
This is how we create the endpoint in the cdk:
props.apiStack.createEndpoint("GET", "/clinics/{clinicID}/credits/stats", getCreditsStats, {
authorizationType: AuthorizationType.COGNITO,
requestParameters: {
"method.request.header.x-user-auth": true,
"method.request.path.clinicID": true
},
requestTemplateBody: `{
"httpMethod": "$context.httpMethod",
"token": "$input.params('x-user-auth')",
"clinicID": "$input.params('clinicID')"
}`,
});
And this is how the createEndpoint method looks like:
public createEndpoint(method: string, path: string, lambda: Function, props: EndpointProps): Method {
const { authorizationType, requestParameters, requestTemplateBody } = props;
const integration = new LambdaIntegration(lambda, {
proxy: false,
requestParameters: Object.keys(requestParameters || {}).reduce(
(o, key) => ({ ...o, [`${key.replace("method.", "integration.")}`]: key }),
{}
),
requestTemplates: {
"application/json": requestTemplateBody,
},
// TODO Check this param
passthroughBehavior: PassthroughBehavior.NEVER,
integrationResponses,
});
return this.api.root.resourceForPath(path).addMethod(method, integration, {
authorizationType,
authorizer: { authorizerId: this.cognitoAuthorizer.ref },
requestParameters,
methodResponses: this.methodResponses,
});
}
Also, integrationResponse looks like this:
{
selectionPattern: '.*"statusCode": 404.*',
statusCode: "404",
responseTemplates: {
"application/json": `#set ($obj = $util.parseJson($input.path('$.errorMessage')))
{"error": {
"code":$obj.error.code,
"statusCode":$obj.error.statusCode,
"message":"$obj.error.msg"}
}`,
},
responseParameters: {
"method.response.header.Content-Type": "'application/json'",
"method.response.header.Access-Control-Allow-Origin": "'*'",
"method.response.header.Access-Control-Allow-Credentials": "'true'",
"method.response.header.Access-Control-Expose-Headers": "'x-amzn-requestid'",
"method.response.header.Strict-Transport-Security": "'max-age=63072000'",
},
}
I was presuming that if I define it the way I did, it would work, and it does to some extent, we don't receive an error in Cloudwatch anymore, but the frontend cannot pickup the error because for the frontend, it's a 200 OK response.
Any help would be highly appreciated!