Principal Engineer, Architecture & Modernization (Hands-on)

abcfinancial; Poland; On-site; PLN 260,000 - 420,000; Full time

Job summary

ABC Fitness is seeking a Principal Engineer to lead the architecture and hands-on modernization of critical software systems. You will steer the transformation from legacy, database-centric apps to domain-oriented software while keeping compatibility and business continuity intact.

This is a hands-on individual-contributor role, where you’ll influence teams through architecture, production-ready code, and strategic collaboration across engineering, product, security, and data teams.

Qualifications

• Extensive experience designing, building, and operating production backend systems.
• Proven ability to implement and ship features with tangible impact.
• Experience with distributed architectures, scalability, and reliability.

Responsibilities

• Lead software architecture and modernization for legacy systems.
• Contribute hands-on in backend coding across Java, Go, or Node/TS.
• Define domain models, APIs, and service contracts with clear boundaries.
• Guide framework and runtime upgrades, modernization of dependencies.
• Diagnose performance, concurrency, and data-access issues in production.
• Improve data access, persistence strategies, and messaging patterns.
• Establish rigorous testing and code-quality practices.
• Translate architectural risk into prioritized, team-wide execution plans.

Skills

Backend systems

Distributed systems

Hands-on implementation

Tools

Java/Spring Boot

Go (Golang)

Node.js/TypeScript

Job description

ABC Fitness is seeking a Principal Engineer to lead the architecture and hands-on modernization of critical software systems. You will steer the transformation from legacy, database-centric apps to domain-oriented software while keeping compatibility and business continuity intact.

This is a hands-on individual-contributor role, where you’ll influence teams through architecture, production-ready code, and strategic collaboration across engineering, product, security, and data teams.