Distributed architectures have become essential in the modern digital landscape, transitioning from traditional monolithic designs to more scalable, resilient, and high-availability systems. A distributed application consists of programs spread across multiple nodes, enhancing fault tolerance and enabling horizontal scaling. While these systems allow for improved scalability and resilience, they introduce complexity and operational overhead. Distributed computing involves dividing a problem into parts processed by different components, communicating through defined protocols. Various models, like client-server and service-oriented architectures, facilitate different aspects of distributed computing, while cloud computing and SaaS provide scalable infrastructure and software delivery models. The advantages of distributed applications include scalability, availability, transparency, and efficiency, although challenges like data consistency and management overhead persist. Application modernization, driven by the need to remain competitive, often involves refactoring monolithic applications into microservices, using strategies like the "strangler pattern" to transition methodically while leveraging cloud-native technologies.