While building a software startup you must carefully consider the architectural foundation on which your future multi-billion dollar business will be built. This will profoundly influence the trajectory and either set up you for success or a great failure. The software development landscape offers a rich variety of architectural paradigms it's worth examining the case of embracing a long-withstanding architectural marvel that is the Citadel.

The main purpose of Citadel is to stand as a guardian and a symbol of strength. The same attributes you look for in your software architecture. Your software needs to serve as a robust sentinel for your digital aspirations. Citadels originally were thought of as a singular structures housing numerous functions and providing a secure environment for inhabitants. In the realm of software, a monolithic architecture is often similarly designed to be cohesive, efficient, and secure.

So what can we learn from adopting a citadel design in software architecture? In this article, I will try to delve into the rationale for adopting citadel architecture for your software startup and explore how this approach aligns with the purpose of the Citadel: a resilient, all-encompassing fortress that stands as a beacon of stability and dependability. I will try to uncover the advantages of starting from monolithic architecture and how it can contribute to your startup's growth and success.

I will try to guide you through the whole journey, discuss the key principles, and bring some potential pitfalls and best practices to consider when crafting your digital citadel. After this article, you'll gain an appreciation for this design choice and you should be better equipped to make your software startup foundation solid so it can survive any earthquakes which you will experience while building your business. Just as the Citadel withstood the test of time, your software venture, architected with care and purpose, can also endure and thrive in the ever-evolving landscape of the digital world.

Citadel v1 (MVP phase)

You are in the most bumpy phase of the startup lifecycle. You will have to face multiple crossrosroads, changes are natural and should be welcomed. That's the moment when your visionary concepts and aspirations begin to materialize into tangible digital creations. MVP requires a strong architectural foundation. By embracing the approach proposed by me, you will be able to swiftly transform your ideas into functional realities, steering your product towards innovation and quick market validation. At this phase, you should think about your software citadel as a monolithic structure that is built using battle-tested frameworks. Below you can find my justification for why you should pursue this path (paved already by companies like Shopify).

1. Simplicity and Speed: MVP is all about quickly testing your product ideas in the wild and learning from usage data and customer feedback. Even though it might be tempting to create a simple lambda service for some functionalities maintaining a monolithic architecture is inherently simpler compared to any distributed architecture. Monolithic architecture offers speed and agility, allowing your development team to focus on building the core features and functionalities of your product without the overhead of managing multiple services, databases, and communication protocols. This streamlined approach can significantly accelerate development, reducing time to market. Additionally onboarding new engineers will be easier - stepping into a codebase in which you can easily trace data flow will pay off in shorter onboarding periods and fewer overheads on training of a proprietary split of microservices.

2. Cost-Effectiveness: Startups always operate with limited budgets, the monolithic approach is always much more cost-effective in the early stages. Fewer engineers will be required to deploying and maintain a product. Which means you will be able to focus your engineers towards feature development which is crucial for startups seeking to validate their business model and attract initial customers. On top of that, a monolith app can be deployed to a single instance which is always cheaper than any serverless solution.

3. Ease of Iteration: Your team will have to rapidly iterate over user feedback and market insights. In a monolithic architecture, changes can be implemented more swiftly, as there's a single codebase to modify. This ease of iteration enables your business to respond quickly to user needs and evolving market conditions, fostering a truly agile development process.

4. Reduced Complexity: In the early stage of lifecycle your application feature set will be relatively simple. A monolithic architecture minimizes this complexity, making it easier for developers to understand and work with the codebase. This simplicity is beneficial as it makes debugging and troubleshooting easier. Additionally, monitoring of distributed systems is complex and requires a ton of expensive tools to do it properly.

5. Resource Efficiency: Monolith architecture will keep your operational overhead to a minimum, allowing your team to focus on validating an MVP. Managing and monitoring a distributed architecture, as well as ensuring communication and data consistency between services, can be resource-intensive.

6. Easier Testing: During MVP phase usually you do not have a quality assurance team. Making sure that your software is reliable will require extensive testing. The cohesiveness of a single code base makes end-to-end testing easier and will result in much faster resolution of detected issues.

Citadel v2 (Growth phase)

Citadels throughout history have shown an impressive ability to adapt and evolve in response to changing threats and requirements. Similarly, your software startup can take inspiration from this adaptability when evolving initial monolithic architecture to accommodate growth. Here's how a startup's architecture can evolve, much like citadels:

1. Fortification and Expansion: Because you found a product market fit you will be noticed by others (competition, more customers, and bad actors). While constantly facing changing threats, you will have to fortify and expand your software. In the early stages, a monolithic architecture may suffice for an MVP. Still, as the startup gains traction and user numbers increase, it becomes necessary to fortify the infrastructure. This can be achieved through the following steps:

   • Standalone services: When you find a product market fit your software should be battle-tested. Right now team already identified which modules of the system have clear boundaries and single responsibility. Usually, those modules do not require access to the full data model and communication with other modules is clear. Those are perfect candidates for smaller standalone services.

   • Scaling for Performance: Hopefully, when user loads increase, scaling your software becomes critical. Leveraging cloud services and containerization will make horizontal scaling a breeze, ensuring that the system can handle more users and higher workloads. With modern tools like Docker and K8s, this will be a no-brainer for any DevOps engineer and will allow to effectively use resources bought from cloud providers.

   • Data Partitioning and Replication: When your database grows and you are not able to scale app your DB instance vertically (but only when this happens) you will have to think about data partitioning (splitting one DB into smaller ones) and replication strategies (maybe different instance for reading and different for writing). This ensures data availability and performance as your user base expands.

   • Load Balancing and Redundancy: Implement load balancers and redundancy to improve reliability and fault tolerance on any level.

2. Improved Security Measures: You will have to start threatening security very seriously and as citadels reinforce their defences against evolving warfare techniques, your team must bolster their security measures to protect against cyber threats. As the user base and data grow, invest in robust security practices and technologies, such as penetration testing, encryption, authentication, and regular security audits.

3. Resource Allocation: Citadels strategically allocated resources to critical areas based on changing needs. Similarly, you as a company should allocate resources wisely. As the application evolves, it's critical that you can easily allocate engineering efforts and resources to the most critical areas, such as performance optimization, user experience enhancements, and feature development.

4. Optimizing for User Experience: You will have to put a lot of focus into user experience and provide them comfort and shelter similar to Citadels. Gather user feedback and continually improve the application's usability, performance, and responsiveness to ensure customer satisfaction.

5. Disaster Recovery and Resilience: Citadels were often built to withstand sieges and disasters. Similarly, startups should invest in disaster recovery plans and resilience measures to ensure business continuity in the face of unexpected outages or failures.

Final thoughts

In conclusion, the monolithic approach offers a compelling choice for software startups seeking to establish a solid foundation for their digital aspirations. Its simplicity, speed, and cost-effectiveness make it an ideal option for startups in the early stages of development.

As startups mature and their needs evolve, they may eventually need to migrate to a more distributed architectural approach. However, the foundations laid by a monolithic architecture can provide a valuable starting point, enabling startups to build upon their successes and achieve even greater heights.

So, as you embark on the journey of building your software startup, carefully consider the merits of the monolithic approach. Just as the Citadel stood as a bastion of strength and resilience, a monolithic architecture can provide the foundation upon which you can build a thriving and enduring digital enterprise.

Remember, the choice of software architecture is not a permanent one. As your startup grows, you may need to adapt your approach. But for the early stages, the monolithic citadel offers an unyielding foundation upon which to build your dreams.