Synchronous and Asynchronous AWS Decoupling Solutions

Coupling is a measure of how closely connected two functions, modules or applications are. Low coupling is often a good sign of a well architected system and good design practice, since it allows you to lower cost of maintenance and high readability of code.

In this article, I will highlight two approaches to achieve decoupling using Amazon Web Services (AWS): synchronous and asynchronous. With synchronous decoupling it requires both sides to be always available, however, they don’t need to ‘know’ each other. Meanwhile, with asynchronous decoupling, communication is achieved even if the receiver is not available.

Synchronous
In order to achieve synchronous decoupling, an Elastic Load Balancing (ELB) could be used. An ELB distributes incoming application traffic across multiple EC2 instances, in multiple Availability Zones. You can add and remove instances from your load balancer as your needs change, without disrupting the overall flow of requests to your application.

There are two types of ELBs:
1. Application load balancers: work in between your web servers and the application servers, generally doing content-based routing. The nodes of an internal load balancer have only private IP addresses. Therefore, internal load balancers can only route requests from clients with access to the VPC for the load balancer.
2. Classic Load balancer: work in between the public Internet and your web servers.