Senior Backend Engineer (Go or Node.js)

We are currently seeking an experienced Senior Backend Engineer (Go or Node.js) to join our team in support of our US-based partner company. Our partner operates a diversified, M&A-driven platform spanning mobile apps, device licensing, media, and financial services. 

As a Senior Backend Engineer, you will take ownership of the newly acquired VPN product and the additional apps our partner company will be acquiring. Your initial focus will be understanding and stabilizing the existing backend and Go networking engine, closing technical and security gaps, and establishing the engineering foundations needed to evolve the product confidently to a consumer VPN with 10M+ installs, 1,000+ servers in 45+ countries, and users in some of the most restrictive network environments in the world. That engine, a Go library cross-compiled for Android and iOS that embeds a userspace TCP/IP stack and drives the Shadowsocks and WireGuard clients, is the core of the product, and you will be the engineer who understands it, hardens it, and extends it. 

Responsibilities:

• Build and maintain secure, reliable backend systems for private and unrestricted internet access
• Develop and optimize Go services across a polyglot stack including Go, Python, and Node.js
• Work with networking and low-level technologies, including IP packets, userspace networking, proxies, tunnels, and mobile cross-compilation
• Design and evolve mobile APIs with clear contracts, versioning, graceful degradation, and OpenAPI/Swagger documentation
• Improve existing systems through reverse engineering, refactoring, testing, and documentation
• Use AI coding agents to accelerate development, testing, and code review while validating their output
• Collaborate with Product and users to identify problems, validate ideas, and deliver impactful solutions
• Build strong unit and integration test coverage and continuously ship reliable changes to production
• Monitor and improve key metrics such as connection success, API performance, errors, conversion, and retention
• Apply security and privacy best practices across secrets, encryption, cryptographic keys, access controls, and user data
• Reference: Qdqc6J24xIIfCLHbg7IgpkJ5Mttg4kPMDuuqBMWnrsLIYmXTCpu5BmduopmMU8UR

Qualifications:

• 5+ years of professional senior backend engineering experience in an agile environment delivering services that support native mobile applications, with hands-on production experience using:
• Go as a primary language: concurrency (goroutines, channels), networking (net, netstack-style packet handling), cgo/gomobile or similar cross-compilation for Android (.aar) and iOS (.framework/XCFramework)
  
  • Python and Node.js for existing services, scripts, and integrations
  • PostgreSQL (schema design, migrations, performance) and MongoDB or another document store, plus Redis or similar caching
  • AWS: Lambda, S3, RDS, Route 53, IAM, and Docker-based services; familiarity with Terraform/Ansible-managed environments
  • REST API design and documentation (OpenAPI/Swagger), authentication (JWT/OAuth), and rate limiting
  • GitHub for version control and pull-request based workflows; SOLID, Clean Coding, Testing, and CI/CD (GitHub Actions or similar)
• VPN and networking expertise: working knowledge of WireGuard (peer/key management, configuration generation), Shadowsocks or other proxy/obfuscation protocols, OpenVPN, TCP/IP, DNS, TLS, and how packets flow from a mobile OS tunnel interface through a userspace stack (lwIP, gVisor netstack) to a VPN server.
• Experience integrating and operating third-party platforms: Stripe and in-app purchase validation (App Store Server API, Google Play Developer API), analytics and attribution (Amplitude, Firebase, AppsFlyer/Adjust or similar), and observability (Datadog)
• Applied security engineering: secrets management (Vault, AWS Secrets Manager/SSM), encryption of sensitive data at rest, safe cryptographic key generation and storage, dependency and vulnerability scanning, and remediating audit findings.
• Agentic AI proficiency: demonstrated day-to-day use of AI agents (e.g., Claude Code, Cursor, GitHub Copilot agents) to write and review infrastructure code, automate runbooks, and investigate incidents, with strong judgment on verifying AI-generated output before it touches production.
• You have exceptional organizational and analytical skills leading to confident independent delivery, but know when and how to include others and enjoys working in a startup environment
• You have experience building large-scale systems with some technical leadership skills.

Nice to Have:

• Experience building or maintaining a consumer VPN, proxy, or privacy backend, especially censorship-circumvention tooling (Shadowsocks plugins, V2Ray/Xray, obfs4) and server-selection / load-balancing logic across a global fleet  – strongly preferred
• Contributions to or deep familiarity with wireguard-go, gVisor netstack, lwIP, or Shadowsocks implementations in Go  – strongly preferred 
• Experience operating multi-provider infrastructure (AWS plus DigitalOcean, Vultr, Hetzner) and Cloudflare  – strongly preferred
• Event-driven and workflow systems (SQS, step functions, job queues) and building resilient integrations with dependency chains and fallbacks – strongly preferred
• Compliance and data-governance experience (GDPR, CCPA, SOC 2), including data retention policies and handling law-enforcement / data requests for a privacy product
• Kotlin or Swift literacy for pairing with mobile engineers on library integration
• Experience taking over and integrating acquired products or codebases

We offer:

• Full-time, remote work
• Working hours: Monday to Friday, earliest start at 11am CET
• Timely and organized performance reviews

If this seems like the right job for you, we invite you to submit your resume in English. Please keep in mind that resumes in other languages might not be considered.