Reliability design patterns - not SOLID but?

by Marina Novikova (masenovikova@edu.hse.ru)

Reliability is a crucial aspect of software design, ensuring that a system consistently performs as expected under various conditions. While SOLID principles have long been touted as the foundation for creating robust and maintainable code, there exists another realm of design patterns specifically tailored to enhance the reliability of software systems. In this essay, we delve into reliability design patterns and explore how they differ from the well-known SOLID principles.

Reliability design patterns focus on mitigating the risks associated with system failures, downtime, and unpredictable behavior. Unlike SOLID, which primarily addresses issues of code maintainability and flexibility, reliability design patterns tackle challenges related to fault tolerance, resilience, and system stability. These patterns encompass a diverse set of strategies aimed at ensuring that a software system remains dependable in the face of adversity. Some of patterns are:

• Replication

Replication is a design pattern that involves creating multiple copies of data or services to provide redundancy and increase availability. By distributing the workload across multiple instances, replication improves the system's reliability by reducing the single point of failure. The pattern also enables load balancing and can enhance performance in addition to reliability.

• Retry

The retry pattern addresses transient failures by automatically retrying failed operations with exponential backoff. Transient failures can occur due to network issues, temporary unavailability of resources, or other intermittent problems. By incorporating the retry pattern, applications can recover from these failures and improve reliability [1].

• Circuit Breaker

The circuit breaker pattern is a design pattern that prevents a cascade of failures in a distributed system by monitoring the health of external services and breaking the connection if they are unhealthy. The pattern is inspired by the electrical circuit breaker, which cuts off the power when there is a short circuit or an overload. The circuit breaker pattern can improve the availability and performance of your system by avoiding unnecessary requests to failed or slow services, and by allowing them to recover [2].

• Monitoring and Logging

Monitoring and logging are essential aspects of a reliable system. These design patterns involve capturing relevant system metrics and logging events to facilitate troubleshooting and analysis. By monitoring system performance and gathering log data, developers can identify and address potential issues proactively, leading to a more reliable system.

• Timeouts

Timeouts provide a mechanism for setting a maximum allowed duration for an operation. By defining a timeout for various operations, developers can prevent the system from getting stuck indefinitely and improve overall reliability. Timeouts enable systems to fail fast, allowing for more efficient resource utilization and better user experience.

While SOLID principles lay the groundwork for writing maintainable and extensible code, reliability design patterns extend the focus to operational aspects. SOLID emphasizes principles like Single Responsibility and Open/Closed, promoting modular and adaptable code. In contrast, reliability design patterns, such as the Retry Mechanism, address concerns like transient failures in external dependencies.

One key distinction lies in the intent: SOLID is primarily concerned with the internal structure of code [3], while reliability design patterns prioritize the external behavior and resilience of a system. Achieving reliability often involves making trade-offs, such as introducing redundancy, implementing fallback mechanisms, or employing graceful degradation strategies – considerations that go beyond the scope of SOLID principles.

Rather than being mutually exclusive, SOLID principles and reliability design patterns can coexist harmoniously. SOLID provides a solid foundation for writing maintainable and readable code, fostering a codebase that is easier to reason about and modify. Reliability design patterns, on the other hand, add an extra layer of robustness to the system, ensuring that it remains operational in the face of unforeseen challenges.

Consider a scenario where a well-architected system following SOLID principles encounters an external service outage. Here, reliability design patterns, like Circuit Breaker, can be employed to gracefully handle the failure, preventing cascading issues and providing a more resilient user experience. In this way, these two sets of principles complement each other, contributing to the overall health and dependability of a software system.

In conclusion, while SOLID principles provide a solid foundation for writing maintainable and extensible code, they do not directly address the challenges associated with system reliability. Reliability design patterns fill this gap by offering a set of strategies focused on ensuring consistent and dependable system behavior, particularly in the face of unexpected failures. Rather than viewing these principles as conflicting, it is more productive to see them as complementary, with each contributing to the overall resilience and reliability of a software system. By embracing both SOLID and reliability design patterns, developers can strike a balance between code maintainability and system dependability, ultimately delivering robust and trustworthy software solutions.

1. Retry with backoff pattern. AWS. Accessed online: December 24, 2023.
2. Natig Madarov. What are the best practices for implementing the circuit breaker pattern in a microservices architecture?. Linkedin. Accessed online: December 24, 2023.
3. Rubem Vasconcelos. SOLID: The concept behind the code. Dev. Accessed online: December 24, 2023.
4. Eric Freeman, Elisabeth Robson. Head First Design Patterns: Building Extensible and Maintainable Object-Oriented Software 2nd Edition. — ISBN: 978-1-4920-7800-5.
5. Jennifer Boothroyd. What Is a Solid? — ISBN: 978-0-8225-6816-2.