Much has been written about the potential benefits of designing applications using microservices. A fair amount has also been written about the potential pitfalls. On this blog, there’s been a combination of both. As I noted in “Are Microservices the Next Big Thing?”: It’s not the technique itself that makes or breaks a design, it’s how applicable the technique is to problem at hand.
It’s important, however, to understand that “applicable to the problem at hand” isn’t strictly a technical question. The diagram in Philippe Kruchten‘s tweet below captures the full picture of a workable solution:
Philippe Kruchten (@pbpk) October 09, 2014
As Kruchten pointed out in his post ‘Three “-tures”: architecture, infrastructure, and team structure’, the architecture of the system, the system’s infrastructure, and the structure of the team developing the system are mutually supporting. These aspects of the architecture of the solution must be kept aligned in order for the solution to work. In my opinion, it should be a taken as a given that this architecture of the solution must also align with the architecture of the problem as a minimum condition to be considered fit for purpose.
Martin Fowler alluded to the need to align architecture, infrastructure, and team structure in “MicroservicePrerequisites” when he listed rapid provisioning, basic monitoring, and rapid deployment as pre-conditions for microservices. These capabilities not only represent infrastructure requirements, but also “…imply an important organizational shift – close collaboration between developers and operations: the DevOps culture”. Permanent product teams building and operating applications are, in my opinion, an extremely effective way to deliver IT. It must be realized, however, that effectiveness comes with a price tag, in terms of people, tools, and infrastructure.
In “MicroservicePremium”, Fowler further stated “don’t even consider microservices unless you have a system that’s too complex to manage as a monolith”, identifying “sheer size” as the biggest source of complexity. Size will encompass both technical and organizational concerns:
The microservice approach to division is different, splitting up into services organized around business capability. Such services take a broad-stack implementation of software for that business area, including user-interface, persistant storage, and any external collaborations. Consequently the teams are cross-functional, including the full range of skills required for the development: user-experience, database, and project management.
Expanding on this, the ideal organization will be one cross-functional team per microservice/bounded context. Even with very small teams, this requires either significant expenditure or a compromise of how the architectural and social aspects (i.e. Conway’s Law) work together in this architectural style.
Other requirements inherent in a microservice architecture are things like API governance and infrastructure services to support distributed processing (e.g. a service registry). Data considerations that are trivial in monolithic environment like transactions, referential integrity, and complex queries are absent in a distributed environment and facilities may need to be bought or built to compensate. In a distributed environment, even error logging requires special consideration to avoid drowning in complexity:
We replaced our monolith with micro services so that every outage could be more like a murder mystery.
Honest Status Page (@honest_update) October 07, 2015
The overhead in terms of organization, infrastructure, and tooling, whether in ideal or comprised form, will introduce complexity and cost. I would, in fact, expect compromises to avoid costs to introduce even more complexity. If the profile of the system in terms of business value and necessary complexity (i.e. complexity inherent in the business function) warrants the additional overhead, then that overhead can represent a valid solution to the problem at hand. If, however, the complexity is solely created by the overhead, without an underlying need, the solution becomes suspect. Adding cost and complexity without offsetting benefits will likely lead to problems. Matching the solution to the problem and balancing those costs and benefits requires the attention of an architectural role at the application level, rather than relying on each team to work independently and hope for coherence and economy.