Elasticsearch, now part of Elastic Cloud, is a highly modular and extensible search engine built upon numerous Guice Module components that facilitate configuration and interface implementation. With over 100 modules, Elasticsearch employs a sophisticated dependency injection system that simplifies the creation and management of class instances, promoting a composable and maintainable architecture. This modular structure allows for flexibility in extending or replacing built-in functionalities through plugins, as seen in the HTTP server component, which can switch implementations by altering configuration settings. Key modules, such as the AnalysisModule, enable developers to easily augment Elasticsearch's capabilities by integrating additional analyzers, tokenizers, and filters compatible with Lucene. This design not only supports the seamless addition of new features but also accommodates customization to meet specific deployment needs, demonstrating the system's dynamic and adaptable nature.