Senior Software Engineer

Join us in bringing joy to customer experience. Five9 is a leading provider of cloud contact center software, bringing the power of cloud innovation to customers worldwide. Living our values everyday results in our team-first culture and enables us to innovate, grow, and thrive while enjoying the journey together. We celebrate diversity and foster an inclusive environment, empowering our employees to be their authentic selves. Five9 is seeking a Senior Software Engineer to rapidly modernize our internal platform tooling and drive full-stack engineering maturity. This is primarily a hands-on developer role — you will own the transformation of existing internal tools to be 12-factor compliant, building polished front-end interfaces alongside robust back-end services, and embedding world-class telemetry (Grafana, Prometheus, Loki) throughout the platform. You will also provide architectural direction for software supporting our Infrastructure-as-a-Service (IaaS) platforms, orchestration systems, and platform engineering initiatives. You will champion modern 12-factor application design, transition legacy pipelines into Kubernetes-native GitOps workflows, and mentor mid-tier developers — all while keeping shipping velocity high. This is a private cloud/ on-premise infrastructure position. We build and manage our own bare-metal and virtualized data center footprint. Do not apply if your experience is exclusively in public cloud environments (AWS, GCP, or Azure). Candidates must have hands-on, practical experience with physical/ on-premise hardware orchestration, hypervisors, and managing Kubernetes on bare-metal/private-cloud layers. Key Responsibilities 12-Factor Application Modernization (Primary Focus) Rapidly audit and refactor existing internal tools and services to strictly comply with 12-factor application principles — configuration via environment, stateless processes, explicit dependency declarations, disposability, and dev/prod parity. Own end-to-end delivery o