Building Microservices: Designing Fine-Grained Systems

by Sam Newman

Degrading Functionality An essential part of building a resilient system, especially when your functionality is spread over a number of different microservices that may be up or down, is the ability to safely degrade functionality. Let’s imagine a standard web page on our ecommerce site. To pull together the various parts of that website, we might need several microservices to play a part. One microservice might display the details about the album being offered for sale. Another might show the price and stock level. And we’ll probably be showing shopping cart contents too, which may be yet another microservice. Now if one of those services is down, and that results in the whole web page being unavailable, then we have arguably made a system that is less resilient than one that requires only one service to be available. What we need to do is understand the impact of each outage, and work out how to properly degrade functionality. If the shopping cart service is unavailable, we’re probably in a lot of trouble, but we could still show the web page with the listing. Perhaps we just hide the shopping cart or replace it with an icon saying “Be Back Soon!”