Communication Between two microservices using ASP.Net Core WebApi

Question

I have two Microservices. First Service for Customers and Second service for Invoice Service.

In Invoice MicroService, I will save only CustomerId. Using this CustomerId, I would like to retrieve all the related data for Customer Microservice. But i don't know to communicate async.

Any please get me some ideas.

Answer 1

What you are proposing - specifically one service making a direct HTTP call to another - is called tight coupling between services and is an antipattern in Microservices. It essentially turns your application into a distributed monolith - it should be avoided.

One example (there are many options) on how to properly do this asynchronously and with good, clean loose-coupled boundaries would be as follows:

• Your system leverages a message bus (I like AMQP, but there are other options)
• When a customer is created, your Customers Service generates a customer_created event
• Your Invoicing Service subscribes to these events and, when received, makes necessary internal customer_id updates (this is keeping its local data store updated - eventual consistency )
• When your Invoicing Service creates an invoice that requires information from the Customers Service , it generates a cust_invoice_pending event
• Your Customers Service subscribes to this event, and when it sees one, it generates a new message like invoice_customer_detail_push on the bus (note, I'd use an invoice_id in the payload of this message to tie them together)
• Your Invoicing Service subscribes to and sees this data it needs which allows it to populate the rest of the invoice

It may seem like a lot of extra work and complexity, and indeed it is. This is the "hard" part of successful microservices architecture. It takes more discipline and planning up front, but here are the advantages - in this simple case - of the resulting solution versus the distributed monolith you've proposed:

• You could swap out your Invoicing Service or Customers Service with something completely different without ever touching the code in the other service
• You've abstracted away concerns related to authz for both services - they share the Messaging Bus and so long as they can both get to/from that, neither knows about the other
• You can allow future services to monitor and interact with this business process (creating and detailing an invoice) without ever changing code in these two services
• If one of the two services goes down, the other service continues to be fully responsive and any work waiting on the down service to come back online automatically gets queued - it persists outside the calling/receiving service

So, if the benefits are worth the tradeoffs in your case, have at it. But, any time you see two "microservices" communicating directly, it's likely you've lost sight a bit of coupling and need to re-examine how information flows through your system.

Answer 2

I think you need just to send a http request to your second service using the CustomerId as query parameter (or post body, but probably not).

You need to CreateClient in your apps, before to do http requests.

Make HTTP requests using IHttpClientFactory in ASP.NET Core

    var request = new HttpRequestMessage(HttpMethod.Get,
        "domain_second_service/controller/method?customerId=X");
    request.Headers.Add("Accept", "application/json");
    request.Headers.Add("User-Agent", "HttpClientFactory-Sample");

    var client = _clientFactory.CreateClient();

    var response = await client.SendAsync(request);