Microservice Principles and Enterprise IT Architecture

Ruth Malan is fond of noting that “design is fractal”. In a comment on her post “We Just Stopped Talking About Design”, she observed:

We need to get beyond thinking of design as just a do once, up-front sort of thing. If we re-orient to design as something we do at different levels (strategic, system-in-context, system, elements and mechanisms, algorithms, …), at different times (including early), and iteratively and throughout the development and evolution of systems, then we open up the option that we (can and should) design in different media.

This fractal nature is illustrated by the fact that software systems and systems of systems belonging to an organization exist within an ecosystem dominated by that organization which is itself a system of systems of the social kind operating within a larger ecosystem (i.e. the enterprise). Just as structure follows strategy then becomes a constraint on strategy going forward, the architectures of the systems that make up the IT architecture of the enterprise influence its character (for good or bad) and vice versa. Likewise, the IT architecture of the enterprise and the architecture of the enterprise itself are mutually influencing. Ruth again:

Of course, I don’t mean we design the (entire business) ecosystem…We can, though, design interventions in the ecosystem, to shift value flows and support the value network. You know, like supporting the development community that will build apps on your platform with tooling and APIs, or creating relationships with content providers, that sort of thing. And more.

So what does any of this have to do with the principles behind the microservice architectural style?

Separation of concerns, modularity, scalability, DRY-ness, high-cohesion, low coupling, etc. are all recognized virtues at the application architecture level. As we move into the levels of solution architecture and enterprise IT architecture (EITA), these qualities, in my opinion, remain valuable. Many of the attributes the microservice style embody these qualities. In particular, componentization at the application level (i.e. systems as components in a system of systems) and focus on a particular business capability both enhance agility at the solution architecture and EITA levels of abstraction.

Conventionally, the opposite of a microservice has been termed a “monolith” when discussing microservice architecture. Robert Annett, in “What is a Monolith?”, takes an expansive view of the term, listing three ways in which an application’s architecture can be monolithic. He notes that the term need not be pejorative. Chris Carroll, in “A Single Deployment Target is not a Monolith”, prefers the traditional definition, an application suffering from insufficient modularity. He notes that an application whose components run in process on the same machine can be loosely coupled and modular. This holds true when considering the application’s architecture, but begins to falter when considering the architecture of a solution and more so at the EITA level.

In my opinion, applications that encompass multiple business capabilities, even when well designed internally, can be described as monolithic at higher levels of abstraction. This need not be considered a bad thing; where those multiple capabilities are organizationally cohesive, more granular componentization may not pass a cost/benefit analysis. However, where the capabilities are functionally disparate, the potential for redundancy in function, lack of organizational alignment, process mismatch, and data integrity issues all become significant. In a previous post, “Making and Taming Monoliths”, I presented a hypothetical solution architecture illustrating most of these issues. This was coupled with an example of how that could be remedied in an incremental manner (it should be noted that the taming of a solution architecture monolith is most likely to succeed where the individual applications are internally well modularized).

Higher level modularity and DRY-ness enhance both solution architecture and EITA. This applies in terms of code:

.@michaelbolton Any software, all software, is a liability. Business capability is the asset. Achieving capability with less s/w is better.

— !! NO LONGER HERE !! Now on Mastodon or BlueSky (@tastapod) November 21, 2014

This also applies in terms of data:

"You need the have a single source of truth, but not necessarily in one place." @UdiDahan #buildstufflt

— Jef Cλaes (@JefClaes) November 20, 2014

Modularity at the level of solution architecture and EITA is also important in terms of process. Whether the model is Bi-Modal IT or Pace-Layered, it is becoming more and more apparent that no one process will fit the entire enterprise (and for what it’s worth, I agree with Simon Wardley that Bi-Model is a mode short). Having disparate business capabilities reside within the same application increases the risk of collisions where the process used is inappropriate to the domain. When dealing with Conway’s Law, it’s useful to remember “I Fought the Law, and the Law Won”.

Even without adopting a pure microservice architecture for any application, adopting some of the principles behind the style can be useful. Reducing redundant code and data reduces risk and allows teams to concentrate on the core capabilities of their application. Modular solution and enterprise IT architectures have more flexibility in terms of deployment, release schedules, and process. Keeping applications tightly focused on business capabilities allows you to use Conway’s Law to your advantage. Not every organization is a Netflix, but you may be able to profit by their example.