Principal Engineer – Software Architecture and Modernization-3

ABC Financial; Poland; On-site; PLN 460,000 - 470,000; Full time

Benefits offered by this job

Open PTO / Time Off policy

Parental & Pawternity Leave

Fitness reimbursement

Medical/Dental/Vision coverage

Job summary

ABC Fitness is seeking a Principal Engineer to lead the architecture and modernization of critical software systems. You will set engineering direction while remaining hands-on and close to implementation, working across Java/Springboot, Golang, and Node/TypeScript ecosystems.

You’ll shape domain models, APIs, and data access while maintaining production reliability. The role emphasizes cross-team collaboration, architectural judgment, and practical refactoring to keep large systems releasable

Qualifications

• Deep backend and distributed-systems engineering experience.
• Ability to move from architecture into code, configuration, instrumentation, and diagnosis.
• Strong testing and code-quality discipline.

Responsibilities

• Lead software architecture and modernization.
• Define target architecture, module boundaries, and migration paths.
• Stay hands-on in code and contribute to critical implementations and production fixes.
• Design domain models and APIs; improve data access and persistence.

Skills

Backend engineering

Distributed systems

Hands-on implementation

AI-assisted engineering

Tools

Java/Springboot

Golang

Node/Typescript

Job description

Join ABC Fitness and become part of a culture that’s as ambitious as it is authentic. Let’s transform the future of fitness—together! Our Values Best Life We believe great work begins with great people. That’s why our culture is built on respect, trust, and belonging. We create an inclusive environment where every team member can bring their authentic self to work—because diverse perspectives drive innovation and meaningful impact. Growth Mindset We are doers, thinkers, and dreamers. At ABC Fitness, your growth is our investment. Through continuous learning, mentorship, and professional development opportunities, we empower you to reach new heights—personally and professionally. One Team From day one, you’ll be part of a team that collaborates, celebrates, and cares. We move fast, support one another, and have fun along the way. Because when you thrive, we all thrive.

Lead the architecture and hands‑on modernization of critical software systems. ABC Fitness is modernizing critical technology from legacy, database‑centric applications toward well‑designed, domain‑oriented software. This role will provide principal‑level technical leadership for that transformation while protecting compatibility, correctness, and business continuity. As a Principal Engineer, you will set software architecture and engineering direction and remain close to implementation. You will work across application code, domain models, APIs, data access, messaging, runtime behavior, and tests to turn complex technical risk into durable software. This is a hands‑on individual‑contributor role. You will influence teams through technical judgment, clear architecture, working software, production insight, and partnership not through direct people management.

WHAT YOU'LL DO

• Lead software architecture and modernization
• Shape the evolution of legacy applications into well‑structured, domain‑oriented software.
• Define target architecture, module and service boundaries, migration seams, compatibility strategies, and incremental paths that teams can implement safely.
• Stay deeply hands‑on in code
• Contribute directly to critical implementations, prototypes, refactoring, code reviews, and production fixes.
• Work comfortably in backend code and frameworks such as Java/Springboot, Golang, Node/TypeScript, or similar backend ecosystems, and help teams improve application structure, runtime behavior, and maintainability.
• Design strong domain models and APIs
• Create clear domain abstractions, ownership boundaries, service contracts, and APIs.
• Improve how business rules are represented in code and keep consumers insulated from legacy storage and implementation details.
• Modernize application foundations
• Guide framework and runtime upgrades, dependency modernization, concurrency and lifecycle improvements, and the decomposition of tightly coupled code.
• Use practical refactoring strategies that keep large systems releasable throughout the work.
• Engineer for correctness, performance, and reliability
• Diagnose difficult behavior through code, runtime evidence, database interactions, and dependency flows.
• Fix root causes in implementation and design, including concurrency defects, inefficient data access, resource contention, failure propagation, and recovery behavior.
• Improve data access and integration design
• Move business logic out of database‑centric implementations and into testable application code.
• Design effective persistence, transaction, caching, messaging, and event‑consumer patterns while preserving historical, reporting, and audit needs.
• Raise the bar for code quality and testing
• Establish strong practices for unit, integration, contract, and functional testing.
• Improve code review, static analysis, dependency management, feature controls, and validation so teams can change complex software with confidence.
• Create reusable engineering patterns
• Turn successful designs into clear patterns, reference implementations, libraries, and architecture decisions that help teams solve recurring software problems consistently.
• Turn technical strategy into cross‑team execution
• Translate architectural risk into clear code‑level priorities, decisions, ownership, and sequenced implementation plans.
• Partner with engineering, product, security, and data teams to move complex software initiatives from design through working code.

WHAT THIS IS NOT

This is not a people‑management or architecture‑only role. The engineer is expected to contribute directly to implementation and production outcomes. This is not limited to greenfield design or modernization for its own sake. Decisions must balance long‑term software quality with migration safety, business value, and the realities of changing production applications.

WHAT YOU BRING

• Deep backend and distributed‑systems engineering
• Credible hands‑on implementation depth You can move from architecture into code, configuration, instrumentation, and diagnosis. Exact experience with Java/Springboot or Golang or Node/Typescript is relevant, but the key here is moving ideas into shippable software solutions and not on the technology.
• Service transformation and architecture judgment You can define service boundaries, domain ownership, migration strategies, integration patterns, and practical architecture decisions for complex existing environments.
• Production reliability and performance expertise You can trace difficult behavior through application code, runtime state, database interactions, and dependency flows, then implement fixes that improve correctness, concurrency, performance, and recovery behavior.
• Software design and refactoring depth You can improve large codebases through domain modeling, modular design, dependency management, incremental refactoring, and carefully chosen abstractions. You know how to create better seams without forcing risky rewrites.
• Data and integration depth You understand relational databases, SQL behavior, messaging, event consumers, data movement, caching, and the tradeoffs involved in separating applications from legacy data dependencies.
• Strong testing and code‑quality discipline You treat automated testing, code review, static analysis, dependency health, secure coding, and production validation as essential parts of software design—not downstream concerns.
• Principal‑level technical leadership You create clarity across teams, challenge weak assumptions constructively, communicate risk in business terms, and help groups converge on decisions they can execute.
• An opportunity‑focused approach to AI‑assisted engineering You actively look for ways AI can expand engineering leverage across code comprehension, design exploration, implementation, refactoring, test generation, debugging, documentation, and planning. You help turn promising uses into repeatable practices that make strong engineers more effective.

BONUS POINTS

• Experience modernizing large complex software systems, including runtime and framework upgrades.
• Experience decomposing monoliths, extracting services, or establishing modular boundaries within large existing applications.
• Experience with Oracle or other enterprise relational databases, Kafka or similar messaging systems, and complex data migration or reporting dependencies.
• Experience with profiling, runtime instrumentation, concurrency analysis, database‑performance diagnosis, or tuning.
• Experience applying AI coding agents for codebase analysis, implementation, testing, and software modernization.

WHAT SUCCESS LOOKS LIKE

• Modernization advances without destabilizing the business ; Critical migrations have clear boundaries, sequencing, ownership, and safety controls. Teams retire legacy constraints while maintaining compatibility and operational continuity.
• Critical software becomes easier to change; Codebases have clearer boundaries, stronger tests, healthier dependencies, and fewer hidden couplings. Teams can add capabilities and modernize incrementally without destabilizing unrelated behavior.
• Architecture decisions become executable; Teams understand the target state, the next practical step, and the tradeoffs behind key decisions. Cross‑team dependencies and risks are surfaced early and actively managed;
• Engineering quality improves across the lifecycle; Test coverage, code review, static analysis, dependency health, and production validation become stronger and more consistent across the software in scope;
• AI expands engineering leverage; AI becomes an effective part of how teams understand code, explore designs, implement changes, generate tests, diagnose problems, and document systems.

Why This Matters

ABC Fitness depends on critical software and data flows that must evolve without compromising the businesses and members they support. Strong architecture is valuable only when it produces clearer code, better behavior, and software that teams can continue to change. This role connects long‑term technical direction with hands‑on software engineering. Done well, it will help teams reduce codebase complexity, modernize with confidence, resolve production problems at their source, and build a stronger foundation for future product development.

Compensation for this role

Compensation for this role will be determined based on a variety of factors, including relevant experience, qualifications, skills, geographic location, and market considerations. The anticipated compensation range for this position is - PLN 460,000.00 - 470,000.00- annually. In addition to base compensation, eligible employees may be offered other forms of compensation, such as bonuses, commissions, equity, or other incentive programs, where applicable. Compensation and benefits may vary by location and are subject to applicable legal, business, and market requirements.

WHAT’S IN IT FOR YOU:

• Purpose led company with a Values focused culture – Best Life, One Team, Growth Mindset
• Time Off – with our open PTO policy, you pick when you want time off when it’s best for you!
• Days of Disconnect – once a quarter, we take a collective breather and enjoy a day off together around the globe. #oneteam
• Parental & Pawternity Leave – we offer leave for when your family grows by two feet or four paws!
• Fitness Perk – we are committed to meeting you wherever you are in your fitness journey with a quarterly reimbursement.
• Discounts – access to discounts with our partners, such as Dell, Microsoft & many more.
• Medical/Dental/Vision coverage.
• EAP – we get you help when you need it. Period.
• Calm App +4 – enjoy tranquility with a Calm App subscription for you and up to 4 dependents over the age of 16.
• And more! – so many benefits we couldn’t even fit them all here!

ABC’S COMMITMENT TO DIVERSITY, EQUALITY, BELONGING AND INCLUSION:

ABC is an equal opportunity employer committed to diversity, equity, and inclusion. We strive to create a workplace where every employee, client, and partner feels valued, inspired, and empowered to reach their full potential. For us, inclusion isn’t just the right thing to do—it’s a business imperative. Learn more at abcfitness.com.

About ABC Fitness

ABC Fitness is the #1 software provider for fitness businesses of any size, all around the world. Supporting 30K clubs, 650K coaches, 40M members, and processing more than $12B in payments every year, ABC Fitness provides scalable, data‑driven solutions to simplify club management and engage members and clients. From personal trainers, boutique studios, and gyms, to international franchise health clubs, ABC Fitness will move your business forward through technology and industry insights. Innovation is at the center of everything we do, across ABC Glofox, ABC Ignite, ABC Trainerize, and ABC Evo. Let’s make your fitness vision a seamless reality, together. Learn more at abcfitness.com #LI-REMOTE We have achieved this through constant pursuit of new developments and innovations in an exciting team environment. Likewise, ABC contributes to our employees’ futures. In addition to our outstanding employee benefits, employees also receive training on an on‑going basis allowing them to develop their strengths and move up in the company.