Microservices for the monolith

I found this post in my drafts folder. It’s about three years old, and I was going to delete it; but I had a quick read and there were a few things that are still worth saying.

It dates back to when there was a lot of excitement about microservices and I was researching them for an employer. Ultimately, the technical demands of maintaining microservices were too much for a company that had bigger problems – but the principle involved (microservices as service-oriented architecture done right) were incredibly useful.

Foremost among these useful principles was the idea of treating all interactions as inherently asynchronous and unreliable. The principles in the Fallacies of Distributed Systems are a useful caution for almost all projects. Although I’m not convinced Conway’s Law is either valid or useful.

Now that we’ve got big data out of the way, it looks as if the next big hype will be microservices. The term has been around for a while, most notably in a January 2013 talk by James Lewis of Thoughtworks. The idea started to become popular around February 2014, with Martin Fowler publishing a post on the subject in March. Discussion is gathering, with a conference, Mu-Con, planned for the end of November and an O’Reilly book on the topic due for publication in March 2015.

As with Big Data, there is a similar lack of clarity about the definition. How tiny is micro? Definitions have ranged to a couple of screens of code, to a small amount of code that a single developer can understand in a few days. James Lewis suggested about 1000 lines long.

Regardless of the problematic definition, obvious characteristics of such services are emerging, with JSON and REST are forerunners for the protocols. Netflix have been open about their successes with this architecture, releasing some amazing tools and documentation.

A purist microservice architecture is not going to be helpful for most companies. In his early presentation, James Lewis mentioned the importance of Conway’s law. Microservices require highly-skilled developers, clearly defined structure and rigourous processes. Most companies are unlikely to have the structure, processes and calibre of developer to make full use of these architectures, let alone convert their existing architecture to fit in with this new way of working.

Despite this, microservices are still relevant to every Java developer, even if you’re working with a monolithic ball-of-mud architecture. It’s a rare system that doesn’t need to integrate with some external service. Microservices teach us to treat any external system as potentially unreliable and incompetent. If the service takes too long to reply, how does that effect our SLAs?

Netflix are so confident of the resilience of their server eco-system that they have introduced the chaos monkey. This turns off services randomly during business hours, to make sure that service continues uninterrupted. Because failures are going to happen so you should treat that as a fact of life. You system might be up 99.9% of the time, but it’s the 0.01% that gets remembered in your annual review.

The tools Netflix have produced to deal with these issues are designed to work with thousands of small services, but something like Hystrix is usable for a single integration. You need to be asking; how might this fail? When should I time out? And you can get this power with just a few Spring annotations.

These tools and architectures will be essential for every Java developer. When I first started writing software, everyone knew how important automated tests were, but test harnesses were difficult to produce. The creation of Junit made tests simple to write and this has altered the way Java software is developed, enabling refactoring, continuous delivery, and TDD.

Testing was important before Junit, and there are developers who still don’t use automated tests, but but Junit has revolutionised Java development. The software I am writing now is considerably more sophisticated that what I was writing 14 years ago. In part that is down to new tools like unit testing and Spring.

The tools designed for microservices are simple enough that they should be understood by every developer. The questions faced by Netflix should be considered for any integration: how do I handle failure, what do I do if this is not available?

The scale and size of the systems being build nowadays are incredible, and this has been enabled by the range and skill of the tools that have been open-sourced. Every developer needs to understand the tools created for microservices. Simple architectures should be as reliable as complicated ones.

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