Senior Backend Engineer

About the role

Kasookoo is looking for a Senior Backend Engineer to own the Call Control Engine and Routing Module – the orchestration core of its cloud‑native contact‑center platform. You will design and implement the per‑call orchestration, multi‑leg routing logic and real‑time billing integration that power intelligent, AI‑driven voice interactions.

Key responsibilities

• Build the call‑control runtime that receives calls from the SBC and manages call state throughout the lifecycle.
• Invoke the live routing API with circuit breakers, caching and correlation‑ID tracking to resolve B‑legs.
• Coordinate with the Billing Module for pre‑call authorization, mid‑call timer management and periodic re‑authorization.
• Maintain an active‑call registry, leg correlation and timer management; trigger accurate CDR generation on hang‑up.
• Implement fallback mechanisms for routing API failures and enforce duration limits with graceful termination.
• Generate complete CDRs (metadata, timing, termination reason, billing pulses) and ensure reliable delivery to the customer CDR API with retries, ordering and audit guarantees.
• Develop an API Gateway that fronts all external integrations, applying resilience patterns such as retries, circuit breakers, rate limiting and authentication.
• Create admin and operational tooling, including configuration UIs/CLIs, debug endpoints and monitoring surfaces.

Required profile

• 6+ years of backend engineering experience in a high‑performance language (Java or Node.js) for concurrent, stateful systems.
• 5+ years of API engineering with solid REST and integration experience.
• Hands‑on experience with streaming platforms (Kafka or equivalent) and designing idempotent event producers/consumers.
• Direct experience programming call‑control or B2BUA logic (FreeSWITCH ESL, Kamailio, Asterisk ARI, or a custom SIP stack).
• Strong expertise in concurrency, state‑machine design and real‑time processing.

Required skills

• Java
• Node.js
• REST APIs
• Kafka (or equivalent streaming system)
• SIP
• FreeSWITCH ESL
• Kamailio
• Asterisk ARI
• Concurrency
• State machines