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 of modernized services: back-end APIs (Go/Python) paired with clean, functional front-end interfaces (React or Vue) that surface platform data and controls to internal users. Decompose monolithic or ad-hoc scripts into properly structured, independently deployable services with clearly defined interfaces.

Full-Stack Development Build and maintain internal web UIs using modern front-end frameworks (React or Vue) — dashboards, tooling consoles, and operational interfaces that teams actually want to use. Design and develop robust REST/gRPC back-end APIs in Go and Python following clean architecture patterns. Ensure front-end and back-end components are instrumented end-to-end with traces, metrics, and structured logs from day one.

Observability Telemetry Own the platform observability stack: design, implement, and continuously improve our Grafana, Prometheus, and Loki deployment for all internal services. Define and enforce instrumentation standards — every new or refactored service must ship with meaningful RED metrics, structured JSON logs forwarded to Loki, and distributed traces. Build and maintain Grafana dashboards and alerting rules that provide actionable signal for on-call engineers; define and manage SLIs/SLOs across critical platform services.

Implement Prometheus exporters for custom internal services and integrate alerting with PagerDuty or equivalent. Drive log aggregation strategy with Loki — label taxonomy, retention policies, and LogQL query libraries for common operational queries. Architecture API Development Design, develop, and support robust APIs and automation services from scratch using Go and Python.

Conduct architecture reviews and enforce design standards across the platform engineering team. Drive the modernization of legacy platform components with a bias toward simplicity and operational transparency. CI/CD GitOps Transformation Lead the refactoring of existing deployment pipelines to be fully Kubernetes-native.