X-Ray Tracing Modes (https://docs.aws.amazon.com/lambda/latest/dg/API_TracingConfig.html).
Lambda will respect any tracing header it receives from an upstream service.
If no tracing header is received, Lambda will call X-Ray for a tracing decision.
Lambda will not trace any request.
Lambda will only trace the request from an upstream service if it contains a tracing header with “sampled=1”.