What is the total number of spans in a web application using a microservice architecture when the request chain includes a load balancer, authentication service, billing service, and resource request?

In a microservice architecture, each service or component that processes a request contributes a span to the overall request chain. A span typically represents a single unit of work or an operation within the architecture.

In the scenario described, you have several components:

1. The load balancer, which routes the incoming request.

2. The authentication service, which handles user authentication.

3. The billing service, which processes billing operations related to the request.

4. The resource request, which typically represents the actual retrieval of the service or resource that the user is seeking.

Each of these components represents a separate span since each one is a discrete operation that affects the overall response to the user’s request. Therefore, when you account for the load balancer, authentication service, billing service, and the resource request itself, you arrive at a total of four spans.

Additionally, understanding that spans can also represent nested operations can help clarify why no additional spans are added in this case. Each component operates linearly rather than hierarchically without additional interactions or nested calls altering the total count.

Thus, the correct answer reflects that there are four distinct operations contributing to the request chain.