What is the scalable approach for executing post tasks regarding on specific operation?

I'm working on B2B microservice platform. The scenario is to buying and sell product from one business to another business, I meant not a person to business like e-commerce. When one business order product from another business I've to send invoice over email, mobile SMS, push notification etc to both buyer and seller business employees (each business can have multiple employees).So what I'm doing now, when an order created I'm fetching employee information related both buyer and seller business from another service by API call and calling another service over API to send the invoice over sms email etc based on user preference. same for update the order.when demand increases as it's the basic feature of this platform sometime seems it slows down the ordering process. Here I'm using expressjs , mongodb in backend on ubuntu VM.Should I use any message-broker to handle those task? or another worker (child) process to handle them? whats your suggestion and how should I go forward?

Submitted November 16, 2018 at 09:33PM by osmangoninahid