Stateful applications require data persistence. A typical example is the deployment and management of containerized databases, a cornerstone for any robust cloud-native architecture. Usually, these use cases are more complex than stateless applications and require the simultaneous application of multiple YAML files, streamlining the configuration process in Kubernetes environments. Delving deeper, the chapter explores the cloud-native Software Development Lifecycle (SDLC), offering insights into the best practices and methodologies that underpin successful cloud-native deployments. Complex applications mark an increase in the realm of polyglot, multi-language cloud application development, highlighting the versatility and adaptability required in today's diverse technological landscape.