Monolithic applications are mostly developed and enhanced based on the technologies primarily used during the initial development of a project or a product. This makes it very difficult to introduce new technology at a later stage of development or once the product is in a mature state (for example, after a few years). In addition, different modules in the same project that depend on different versions of the same library make this more challenging.

Technology is improving year on year. For example, your system might be designed in Java and then, a few years later, you may want to develop a new service in Ruby on Rails or Node.js because of a business need or to utilize the advantages of new technologies. It would be very difficult to utilize the new technology in an existing monolithic application.

It is not just about code-level integration, but also about testing and deployment. It is possible to adopt a new technology by rewriting the entire application, but it is a time-consuming and risky thing to do.

On the other hand, because of its component-based development and design, microservices architectures give us the flexibility to use any technology, new or old, for development. They do not restrict you to using specific technologies, and give you a new paradigm for your development and engineering activities. You can use Ruby on Rails, Node.js, or any other technology at any time.