When IOC containers become an anti-pattern
Author: Kasper B. Graversen
[Introduction] [All categories] [All articles] [Edit article ]
Architecture Micro Service Refactor to Micro Services Dependency Injection IOC IOC Container Service Locator
For many years IOC containers have been touted the tool that ensure testable and reusable software. Any large enterprise project with self respect uses one. Interestingly, when refactoring to micro services, IOC frameworks play less of a role - To the extend, that their use may be regarded an anti-pattern.
Please show your support by sharing and voting:
Table of Content
1. Historical background
First at bit of history to set the scene. Around 2005-2006 people started writing about dependency injection in MSDN Magazine and Dr. Dobbs. With the popularization of dependency injection techniques, the ecosystem of IOC container frameworks proliferated, giving further momentum to the movement. Inevitably, IOC containers became modern. There was excitement. Finally, we had the technique, and tool support, for creating testable code. Heck, I was excited too. Enterprise software, unit testing, maybe even a bit of TDD - combined!
In any modern larger software project with self respect, you will find the use of an IOC framework. If you're not using IOC containers, you'll hear experienced programmers complain your ears off about it. Nothing wrong with that. Their benefits generally out-weigh the introduced complexity. At least so long as they are not used as service locators. Personally. I've done magic with IOC containers! Test-enabling a behemoth of an application framework that otherwise was not impenetrable to testing. But more on that another time.
Before we continue, it is important to the terminology straight. There are two closely related concepts that are easily mixed up on the Internet. These are;
- Dependency injection is a programming practice of passing into an object it’s collaborators, rather the object itself creating them. For example, "constructor injection" is the technique of taking all "static dependencies" as constructor arguments.
- An IOC Container/Dependency injection frameworks is a framework, that can create instances of object graphs and their dependencies. Typically through some explicit configuration or implicitly by scanning assemblies combined with conventions of naming or use of attributes.
So you can do dependency injection perfectly fine without an IOC container if you so choose.
2. IOC containers as an anti-pattern
Part of my job at MVNO, is to tease apart functionality of a large monolith, and placing it in independent micro services. Independent of each other, we made an interesting observation.
The first thing we do after moving the code to the micro service,
almost as a knee-jerk reflex,
is to remove the dependency to the IOC framework.
It's not that we don't like IOC frameworks, they're great! But in the context of micro services, IOC containers often do not have a role to play. Part of what defines a micro service, is that it is small. Hence the number of composition roots are limited. It may therefore be just as easy to instantiate the object graph by hand. In a micro service implementation, using an IOC framework may be regarded an anti-pattern - if you have a need for an IOC framework, it may be an indicator, that your service is too big.
Cutting the ties to the IOC container dependency yields the following advantages
- No registering of interfaces to types.
- No life-time management.
- One less dependency to manage when building and deploying.
Make no mistake. We do a whole lot of dependency injection - we just don't employ an IOC framework.
In terms of testable code, it is the practice of using dependency injection that enables testability, not the IOC framework.
In a micro service implementation, using an IOC framework may be regarded an anti-pattern - if you have a need for an IOC framework, it may be an indicator, that your service is too big.
Please show your support by sharing and voting:
August 2016 NOTICE: MVNO IS HIRING MVNO at Telenor is looking for talented developers. MVNO is the infrastructure that keep mobile companies running. Our clients include CBB, Bibob, and OK Mobil.
MVNO offers a unique culture where a big part of the working life if about optimizing for happiness. Your happiness! We have 20% of our time allocated for innovation or fixing stuff that bothers us. Great work place with 37h work week, six weeks vacation and highly skilled friendly colleagues.
If you are interested please contact firstname.lastname@example.org for further details. The office is situated at Telenor Copenhagen.
Congratulations! You've come all the way to the bottom of the article! Please help me make this site better for everyone by commenting below. Or how about making editorial changes? Feel free to fix spelling mistakes, weird sentences, or correct what is plain wrong. All the material is on GitHub so don't be shy. Just go to Github, press the edit button and fire away.
Read the Introduction or browse the rest of the site