We present a cloud-native threat hunting architecture built on open-source technologies. The security architecture integrates SysFlow and Kestrel to provide connected endpoint observability, edge analytics, and a cyber-reasoning stack that enables threat hunters to quickly and uniformly perform threat hunting and investigation across cloud and premise environments. This facilitates a new threat discovery methodology in which declarative hunting flows automate the search for behavioral attack patterns and indicators of compromise in telemetry data streams that are automatically tagged with attack TTPs. We show how these two open-source frameworks can deploy and scale natively on cloud environments to discover attacks and security breaches against cloud services and container infrastructures. SysFlow is an open observability framework that lifts and normalizes the representation of system activities into a compact entity-relational format that records workload behaviors by connecting single-event and volumetric flow representations of process control flows, file interactions, and network communications. It drastically reduces data footprints over existing approaches and is particularly suitable for large scale cloud-wide monitoring and forensic investigation of sophisticated cyber-attacks that may not be discovered for long periods of time. Kestrel is a threat hunting language for creating composable, reusable, and shareable hunt flows. It brings two key innovations to the security community: (i) a composable way of expressing hunting knowledge for threat hypothesis development and reasoning over entity-relational data abstractions, and (ii) an open-source language runtime to compute how to perform hunting steps and execute them in a distributed fashion at the local hunting site, remote data sources, and in the cloud. We will demonstrate through live threat hunting scenarios how the two open-source projects can help create a powerful open platform for gaining operational awareness and alleviating key pain points in integrating security solutions into a "single-pane-of-glass" for effective and shareable threat hunting in the cloud.