solid principles in microservices

When microservices encounter "hard bones": How SOLID can help you solve it

So someone asked, are there any principles that can make these scattered small services independent and reliable? There really is, and the answer is hidden in five capital letters: SOLID. This is not some trendy theory, but a time-tested core principle of programming. Applying it to microservice design is like finding a reliable servo motor for a complex mechanical system - each part has clear responsibilities and stable operation, and only when combined can it be precise and powerful.

What exactly is SOLID?

Simply put, it is the abbreviation of five design concepts that guide us to write code that is more maintainable and flexible. In the world of microservices, they become the "traffic rules" of service design.

• S - Single responsibility: one service, one big thing.This is like a steering gear that is only responsible for accurately controlling one angle of rotation. Don't let one user service take care of both logging in and sending emails, and still count points. If you do one thing well, you will know where to look if there is a problem.
• O - Open and closed: The service should be easy to expand, but don't change the core all the time.Imagine adding a new sensor to your robot without having to rewrite the main control board, just plug in the interface. Services should also be like this, by adding new modules to respond to new needs, rather than repeatedly modifying old code.
• L - Liskov replacement: The child service must be able to seamlessly replace the parent service.If you upgrade the version of a certain service, other services that call it should be completely innocuous, just like replacing more durable gears, and the machine will still run smoothly.
• I - Interface isolation: Don't force services to use things they don't need.Don't create a huge and bloated "universal interface". Only provide the connection points your customers really need. It's like providing the actuator with only the control signals it needs, rather than cramming the entire control cabinet drawing.
• D - Dependency Inversion: Rely on abstractions rather than concrete implementations.Higher-level services should not rely heavily on the specifics of lower-level services. They should be based on a stable "protocol" or "interface" conversation. This is like defining the grasping instruction standard of the robotic arm. As for whether to use a stepper motor or a servo motor to implement the following, the senior management does not need to care, so that you can replace more useful parts in the future.

Why bother with this in microservices?

Because microservices are inherently prone to chaos. Without these built-in disciplines, so-called “agility” can quickly turn into “fragility.” Following SOLID, you will feel some real changes:

Changes became localized. If you think about the order process, you usually only need to touch the order service itself, and you don't have to worry about checking whether users, inventory, and payment will crash. Testing is also easier because each service has clear boundaries and can be verified independently.

Team collaboration is smoother. The service interfaces are clearly isolated, and there is no need for excessive coordination between teams. As long as they abide by the agreed "contract", they can develop their own modules in parallel, just like assembling a sophisticated machine, and each is responsible for assembling their own components.

Technology selection can be bolder. Because it relies on abstract interfaces, if one day you feel that the database or programming language of a certain service should be changed, as long as the new implementation conforms to the old interface, it can be replaced smoothly without causing a chain earthquake.

How to "knead" these principles into design?

This is not copying a textbook, but a habit of thinking. When designing a new service, stop and ask yourself a few questions: What is its primary value? How is it most likely to change in the future? What is its minimum commitment to external exposure?

Start with a small practice. For example, check an existing service to see if it does more than two core things? Could it be split into two more focused services? Or, look at the calls between services. Are they too dependent on the table structure of the other party's database? Can a clear API contract be defined to decouple it?

This process is a bit like usingkpowerBuild an automation mechanism using precision components: You first plan the independent functions and interfaces of each motor and each steering gear, and then assemble them through a stable communication protocol. Each unit is reliable, and the combined system is both flexible and robust. SOLID principles are the language that helps you draw this reliable assembly blueprint.

Of course, theory is gray, but the tree of practice is evergreen. The real challenge always lies in the specific business logic and ever-changing requirements. But holding the SOLID tool set in your hand can at least give you a clear base map when dismantling a complex system. Knowing where to start can make the structure more stable instead of more chaotic. After all, a good architecture is not a miracle built once and for all, but a design that allows the system to remain sober after countless modifications and growth.

Established in 2005,kpowerhas been dedicated to a professional compact motion unit manufacturer, headquartered in Dongguan, Guangdong Province, China. Leveraging innovations in modular drive technology,kpowerintegrates high-performance motors, precision reducers, and multi-protocol control systems to provide efficient and customized smart drive system solutions. Kpower has delivered professional drive system solutions to over 500 enterprise clients globally with products covering various fields such as Smart Home Systems, Automatic Electronics, Robotics, Precision Agriculture, Drones, and Industrial Automation.