You can implement microservices-based design on both new and existing products and services. Contrary to the belief that it is easier to develop and design a new system from scratch rather than making changes to an existing one that is already live, each approach has its own respective challenges and advantages.

For example, since there is no existing system design for a new product or service, you have freedom and flexibility to design the system without giving any thought to its impact. However, you don't have the clarity on both functional and system requirements for a new system, as these mature and take shape over time. On the other hand, for mature products and services, you have detailed knowledge and information of the functional and system requirements. Nevertheless, you have a challenge to mitigate the risk of impact that design change brings to the table. Therefore, when it comes to updating a production system from monolithic to microservices, you will need to plan better than if you were building a system from scratch.

Experienced and successful software design experts and architects always evaluate the pros and cons and take a cautious approach to making any change to existing live systems. One should not make changes to existing live system design simply because it may be cool or trendy. Therefore, if you would like to update the design of your existing production system to microservices, you need to evaluate all the pros and cons before making this call.

I believe that monolithic systems provide a great platform to upgrade to a successful microservices-based design. Obviously, we are not discussing cost here. You have ample knowledge of the existing system and functionality, which enables you to divide the existing system and build microservices based on functionalities and how those would interact with each other. Also, if your monolithic product is already modularized in some way, then directly transforming microservices by exposing an API instead of Application Binary Interface (ABI) is possibly the easiest way of achieving a microservice architecture. A successful microservices-based system is more dependent on microservices and their interaction protocol rather than anything else.

Having said that, it does not mean that you cannot have a successful microservices-based system if you are starting from scratch. However, it is recommended to start a new project based on monolithic design that gives you perspective and understanding of the system and functionality. It allows you to find bottlenecks quickly and guides you to identify any potential feature that can be developed using microservices. Here, we have not discussed the size of the project, which is another important factor. We'll discuss this in the next section.

In today's cloud age and agile development world, it takes an hour between making any change and the change going live. In today's competitive environment, every organization would like to have an edge for quickly delivering features to the user. Continuous development, integration, and deployment are part of the production delivery process, a completely automatic process.

It makes more sense if you are offering cloud-based products or services. Then, a microservices-based system enables the team to respond with agility to fix any issue or provide a new feature to the user.

Therefore, you need to evaluate all pros and cons before you make a call for starting a new microservices-based project from scratch or planning to upgrade the design of an existing monolithic system to a microservices-based system. You have to listen to and understand the different ideas and perspectives shared across your team, and you need to take a cautious approach.

Finally, I would like to share the importance of having better processes and an efficient system in place for a successful production system. Having a microservices-based system does not guarantee a successful production system, and monolithic application does not mean you cannot have a successful production system in today's age. Netflix, a microservices-based cloud video rental service, and Etsy, a monolithic e-commerce platform, are both examples of successful live production systems (see an interesting Twitter discussion link in the Reference section later in the chapter). Therefore, processes and agility are also key to a successful production system.