As federal and defense organizations increasingly adopt open-source geospatial technologies, the need for robust, secure, and enterprise-ready solutions has never been greater. This presentation shares real-world lessons from supporting CoreSpatial—a modular geospatial platform built entirely on open standards and open-source components—in mission-critical environments. Drawing on operational deployments across DoD and civilian agencies, we'll explore strategies for achieving scalability, security, and long-term maintainability with software like GeoServer, GDAL, PostGIS, OpenLayers, Cesium, and MapStore2. Attendees will gain actionable insights on avoiding common pitfalls, establishing sustainable support models, and tailoring open-source stacks for high-stakes federal use cases.