Microservices architecture principle #2: Autonomy over coordination

This post is part of a six-part series on Microservices Principles. Other parts are: Business Capability, Small bounded context, Asynchronous Communication, Best Technology and One Team.
 
Microservices are a hot topic. Because of that a lot of people are saying a lot of things. To help organizations make the best of this new architectural style Xebia has defined a set of principles that we feel should be applied when implementing a Microservice Architecture.
This blog explains why we prefer autonomy of services over coordination between services.
Our Xebia colleague Serge Beaumont posted “Autonomy over Coordination” in a tweet earlier this year and for me it summarised one of the crucial aspects for creating an agile, scalable and robust IT system or organisational structure. Autonomy over coordination is closely related to the business capabilities described in the previous post in this series, each capability should be implemented in one microservice. Once you have defined your business capabilities correctly the dependencies between those capabilities are minimised. Therefore minimal coordination between capabilities is required, leading to optimal autonomy. Increased autonomy for a microservice gives it freedom to evolve without impacting other services: the optimal technology can be used, it can scale without having to scale others, etc. For the team responsible for the service the advantages are similar, the autonomy enables them to make optimal choices that make their team function at its best.
The drawbacks of less autonomy and more coordination are evident and we all have experienced these. For example, a change leads to a snowball of dependent changes that must be deployed at the same moment, making changes to a module requires approval of other teams,  not being able to scale up a compute intensive function without scaling the whole system, … the list is endless.
So in summary, pay attention to defining you business capabilities (microservices) in such a manner that autonomy is maximised, it will give you both organisational and technical advantages.
 
[edited: 3 aug 2015 – added preamble and removed line “Over the next couple of days we will cover each of these principles in more detail in a series of blog posts.“]