What are the best software architecture patterns for e-commerce and online marketplaces?

For e-commerce, leverage isomorphic rendering for faster page loads, ensuring a seamless user experience. Adopt headless commerce architecture to decouple frontend and backend, allowing flexibility. Embrace MACH principles (Microservices, API-first, Cloud-native, Headless) for scalable and adaptable backend systems. Apply Domain-Driven Design principles, defining clear boundaries, aggregates, and domain events for managing complexity effectively. These architecture patterns collectively enhance performance, flexibility, and scalability in e-commerce and online marketplaces.

Monoliths have the advantage of generally being easier to initially implement and they can perform and scale quite well up to a certain point. It can be tempting to go for more complex approaches such as microservices, but there is also a development cost in the form of solving harder issues such as data sync in the DB, maintenance of several apps, as well as managing communication among these microservices and testing. It is important to closely monitor your monolith and progressively mutate to another architecture, like microservices or EDA, when noticeable dips in performance or development speed are noted.

A microservices architecture breaks down the application into independent, self-contained services that communicate with each other through APIs. This pattern provides greater flexibility, scalability, and maintainability, making it well-suited for large and complex e-commerce platforms. Microservices is the widely used architecture. Most of the banking, healthcare, and Fortune companies use microservices as it makes the development easier through APIs.

I would argue that going full serverless for an e-commerce or marketplace platform is quite the technological challenge, but it's worth it if implemented right. On one end, serving the entire frontend as a Single Page Application (SPA) from an S3 bucket is a very popular serverless approach. It's usually served with a Content Delivery Network (CDN) to reduce costs and increase speed. The caveat here is that it can easily become bloated, increasing the Time To Interactive (TTI), thus affecting the user's experience. For the backend you can use AWS Lambda or another serverless solution, but the next problem that arises is the database. Even using DynamoDB it's very easy to bump into issues. I would suggest to use an extendable CMS instead.

There is no single best architecture pattern; it all depends on the scale and conditions. I have worked in an e-commerce company, and in the early stages, we used a monolithic architecture. As the company grew, it began to pose problems, and we decided to migrate to microservices, with some of the services utilizing an event-driven architecture. Each architecture is the best in some situations and bad in others.