Senior Backend Engineer

Castillians

Backend Engineer developing low-latency infrastructure for audio/video communications with AI services integration. Building scalable APIs and handling real-time session management for global team.

Posted 6/11/2026contractRemote • 🇮🇪 IrelandSeniorWebsite

Tech Stack

Tools & technologies

AWSAzureCloudDistributed SystemsFirewallsGoogle Cloud PlatformJavaScriptMicroservices.NETNode.jsPython

About the role

Key responsibilities & impact

Build, deploy, and manage the real-time communication backend to support live audio interactions
Orchestrate end-to-end sessions between end users and backend AI services
Integrate Azure Speech services (STT/TTS) and Azure OpenAI (LLMs) into real-time pipelines
Develop and maintain REST and WebSocket APIs consumed by mobile and web frontends
Handle session state, participant matching, reconnections, and failure recovery as the “traffic controller” for calls
Ensure low-latency, highly available, and scalable infrastructure using containerized microservices
Build backend logic to manage call lifecycle (start/end sessions)
Match participants and track call state
Implement reconnection and failure-handling mechanisms
Act as the system’s “traffic controller” for real-time media sessions
Support for microservices architecture and API scaling

Requirements

What you’ll need

5+ years of backend engineering experience
Strong background in distributed systems
Networking fundamentals (TCP/UDP, NAT, firewalls)
Cloud infrastructure (Azure preferred, but AWS/GCP experience considered)
Proven experience with WebRTC or similar real-time systems (e.g., SIP, RTMP, low-latency streaming)
Experience integrating AI/LLM services into production backends
Ability to work autonomously and mentor junior engineers as needed
Deep understanding of WebRTC connectivity (NAT traversal, firewalls, corporate networks)
Experience with TURN server deployment and management for media relaying
Proficiency in one or more of: Node.js, Python, .NET
Ability to handle audio routing, recording, and optional voice transformations
Hands-on experience with media servers such as: Janus, Kurento, mediasoup

Benefits

Comp & perks

Clear scope with no ambiguity over deliverables.
Opportunity for repeat engagements based on performance.

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills & Tools

backend engineeringdistributed systemsWebRTCREST APIsWebSocket APIsAzure Speech servicesAI/LLM integrationNode.jsPython.NET

Soft Skills

autonomous workmentoring