Self-Contained Systems

Assembling Software from Independent Systems

SCS vs. Microservices

The SCS approach shares a lot of concepts with microservices, including ideas about enforcing isolation via independently deployable units, the alignment of organizational and architectural boundaries, support for diversity in terms of technology choices, and the lack of centralized infrastructure. If you’re willing to see this as the core of microservices, you could view SCSs as a specialization. But compared to some other aspects seen by many people as key attributes of microservices, there are some important differences:

  • A microservice is probably smaller than an SCS. An SCS might be large enough to keep a team busy and provide more meaningful business value.
  • There are usually fewer SCSs than microservices. A logical system such as an e-commerce shop might have 5 to 25 SCSs i.e. for billing, order processing etc. An e-commerce shop might have 100s of microservices.
  • SCSs should ideally not communicate with each other while this is fine for microservices.
  • SCSs have a UI, while microservices might separate the UI from the logic in its own service. However, some definitions of microservices include the UI in the microservice, too.
  • SCSs should favor integration at the UI layer. Microservices typically focus on integration at the logic layer. (Again, some definitions of microservices also allow for integration at the UI layer.)

Of course it is possible to split an SCS even further so it consists of microservices — in particular for the business logic. In this case, this can be seen as a particular micro-architecture approach.

SCS clearly focus on larger projects and a split into multiple teams. Microservices can be used for other purposes: Often small teams or even single developers use them e.g. to use Continuous Delivery more easy, to build more robust systems or to scale each microservice independently. So microservices are more versatile while SCS solve problems specifically with the architecture and organisation of large projects.