Here are 14 essential design principles for microservices:

1. Interface Segregation: Different types of clients (e.g., mobile apps, web apps, CLI programs) should be able to interact with services through the contract that best suits their needs.

2. Deployability: In the microservice era, developers need to make critical design decisions and technology choices regarding packaging, deploying, and running microservices.

3. Event-Driven: Services should be modeled to be activated by asynchronous messages or events instead of synchronous calls.

4. Availability Over Consistency: End users often value the availability of the system over strong data consistency, and they are okay with eventual consistency.

5. Loose Coupling: Microservices should not have a tight dependency on each other to ensure scalability and ease of deployment.

6. Single Responsibility: Each microservice should have a single, well-defined responsibility and should only communicate with other microservices to accomplish tasks.

7. Decentralized Data Management: Each microservice should manage its data without relying on other microservices to ensure scalability and reliability.

8. API-Driven Design: Microservices should be designed around APIs, with each service exposing a well-defined set of APIs for communication with other services.

9. Statelessness: Microservices should be stateless, meaning they should not maintain any client-specific state between requests.

10. Independent and Autonomous/Self-Governing Services: Each microservice should be self-contained and operate independently of all other services in an application.

11. API Aggregation: Microservices should be designed to aggregate APIs for communication with other services.

12. Flexibility: Microservices should be designed to be flexible and adaptable to changing requirements.

13. Scalability: Microservices should be designed to scale independently and handle increased load.

14. Constant Monitoring and Failure Isolation/Resilience: Microservices should be constantly monitored and designed to isolate failures to ensure the overall system remains available and resilient.

These principles help ensure that microservices are designed to be scalable, reliable, and maintainable, making them essential for building robust and efficient microservices-based applications.