Rust Backend Developer

Backend Developer (Rust) – 4connection Messenger Platform

THE 4CONNECTION PROJECT

4connection is a client-commissioned messenger platform combining secure group messaging, interest-based communities, and a serious dating and matching layer. The platform targets the DACH market with a planned launch in early 2027 and a clear commercial roadmap defined with the client, 4connection FlexKapG.

The backend is the proprietary core of the product. The clients (Android in Kotlin, iOS in Swift) will be released as open source. The backend remains closed source.

Architecture highlights:

• Three-layer architecture: Connection Gateway, Routing and Business Logic, Storage
• Cell-based horizontal scaling, approximately 500K users per autonomous cell
• Zero-knowledge server design: message content, keys, and sensitive metadata are not accessible to the server in plaintext
• Custom binary protocol with zero-copy deserialization, no JSON in hot paths
• Event-driven message routing over a NATS bus, no synchronous service waits
• Differentiated storage: Redis for hot state, ScyllaDB for cold history, S3-compatible object store for media

THE ROLE

You will work directly with the technical lead on the Rust backend. The architecture is defined, the stack is chosen, the client is committed, the first internal milestones are running. We are looking for an engineer who wants to take real ownership of significant backend subsystems and write code that will run in production for years.

This is not a Rust learning position. We expect you to be productive in Rust from week one and to bring opinions and experience to the table.

RESPONSIBILITIES

• Implementing backend subsystems in Rust against a clearly defined three-layer architecture
• Building and maintaining the WebSocket and HTTP connection layer (Axum, tokio-tungstenite)
• Implementing message routing and group fanout over NATS
• Implementing the persistence layer against Redis, ScyllaDB, and MinIO
• Implementing the custom binary protocol and zero-copy message handling (rkyv)
• Integrating push notification services (FCM, APNs) without compromising the zero-knowledge guarantees
• Close collaboration with the Android and iOS engineers on API and protocol design
• Writing testable, documented, idiomatic Rust that meets the standard of professional handover

REQUIRED QUALIFICATIONS

• 2+ years of practical Rust experience in non-trivial projects, professional or substantial personal work you can show us
• Solid systems programming background (Rust, C, C++, or comparable) and a real understanding of ownership, lifetimes, memory layout, and concurrency
• Working knowledge of async Rust and the Tokio ecosystem
• Solid network programming foundation: TCP/IP, TLS, WebSockets, HTTP
• Awareness of cryptographic principles relevant to end-to-end encrypted, zero-knowledge systems: key management, forward secrecy, authenticated encryption, secure key derivation. Practical experience is a strong plus.
• A serious commitment to clean, readable, maintainable code. This is non-negotiable.
• Confident with Git and Linux as a daily working environment
• English at B1 or better, written and spoken

DESIRABLE QUALIFICATIONS

• Production experience with Axum, Actix-Web, or comparable Rust web frameworks
• Experience with high-throughput WebSocket systems (tokio-tungstenite, fastwebsockets)
• Experience with zero-copy serialization (rkyv, Cap'n Proto, FlatBuffers) or designing custom binary protocols
• Experience with NATS, Kafka, or comparable message buses
• Experience with wide-column or distributed databases (ScyllaDB, Cassandra)
• Experience with S3-compatible object storage
• Familiarity with FCM and APNs integration
• Familiarity with secure messaging protocols such as Signal Protocol, Double Ratchet, X3DH, or MLS (RFC 9420)

TECHNOLOGY STACK

Rust, Tokio, Axum, tokio-tungstenite, rustls, rkyv, async-nats, Redis, ScyllaDB, MinIO, FCM, APNs, Linux, Git, Open Project, Nextcloud.

HOW WE WORK WITH AI

Claude is used as a language model in our development workflow, as a sparring partner for architecture discussions, code review, and documentation. Claude does not have file system access to our codebase, no agent integration, no automated commits. Source code remains exclusively under the control of the development team. We expect a professional, critical handling of AI tooling. It accelerates thinking, it does not replace engineering judgement.

WHAT WE OFFER

• Fully remote position with long-term collaboration perspective
• Direct mentorship from a technical lead with over four decades of professional software development experience
• A small, focused team without corporate overhead or management layers
• Open-source collaboration tooling (Open Project, Nextcloud)
• Visible work on the open-source client repositories
• Fair compensation aligned with seniority and responsibility

ABOUT WE wilke experience

At WE, we are more than just a service provider, we are a strategic partner. Our more than 40 years of experience in software development and the use of state-of-the-art software-supported processes guarantee the flexible and promising implementation of our projects.

The result of over four decades of experience is an in-depth knowledge of the industry, which enables us to always be at the cutting edge of technology. We are a reliable partner for the development of customized software solutions. We support our customers in turning their visions into reality.

You will always have a dedicated contact person at your side to provide you with advice and support.

With our innovative collaboration tool, WE Gate, we make communication and collaboration simple, transparent and truly agile.

Among other things, we work with collaboration tools, ticket systems, chats, Git, TeamCity, shared documents and further support for remote collaboration.

Company website: https://wilke-experience.de/

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