Diagramming Microservices With the C4 Model

Here's a question I'm being asked more and more... how do you diagram a microservices architecture with the C4 software architecture model?

It's actually quite straightforward providing that you have a defined view of what a microservice is. If a typical modular monolithic application is a container with a number of components running inside it, a microservice is simply a container with a much smaller number of components running inside it. The actual number of components will depend on your implementation strategy. It could range from the very simple (i.e. one where a microservice is a container with a single component running inside) through to something like a mini-layered or hexagonal architecture. And by "container," I mean anything ranging from a traditional web server (e.g. Apache Tomcat, IIS, etc) through to something like a self-contained Spring Boot or Dropwizard application. In concrete terms:

• System context diagram: No changes ... you're still building a system with users (people) and other system dependencies.
• Containers diagram: If each of your microservices can be deployed individually, then that should be reflected on the containers diagram. In other words, each microservice is represented by a separate container.
• Component diagrams: Depending on the complexity of your microservices, I would question whether drawing a component diagram for every microservice is worth the effort. Of course, if each microservice is a mini-layered or hexagonal architecture then perhaps there's some value. I would certainly consider using something like Structurizr for doing this automatically from the code though.

So there you go, that's how I would approach diagramming a microservices architecture with the C4 model.