Senior Backend Engineer

JustBacked; Warszawa; On-site; PLN 180,000 - 300,000; Full time

Job summary

AppsFlyer is seeking an exceptional Backend Software Engineer to join the Domain Team within SaaSLab. You will design, build, and operate backend systems powering accounts, apps, and users, with a focus on scalable data flows and onboarding experiences.

The role demands ownership from design through production in a distributed, cloud-based environment. As part of SaaSLab, you will collaborate across teams to evolve the domain model, adopt GraphQL Federation, and ensure high availability and

Qualifications

• 5+ years of software development experience expected.
• Experience building and operating production-grade distributed systems.
• Strong understanding of design, architecture and best practices.
• Experience with high-scale, cloud-based architectures.
• Ability to own problems from design to production.
• Excellent collaboration and communication across teams.
• Proficiency in written and verbal English.
• B.Sc. in Computer Science or equivalent practical experience.

Responsibilities

• Design, develop, and maintain scalable backend systems and data flows for core entities and onboarding.
• Decouple from legacy data stores and adopt modern patterns like GraphQL Federation.
• Write high-quality, thoroughly tested production code; own features end-to-end.
• Engage in architecture reviews and code reviews to raise the bar.
• Collaborate with product managers, team leads, and engineers to deliver roadmaps.
• Ensure high availability, security, and operational excellence for critical services.
• Troubleshoot production issues and contribute to on-call rotations.
• Stay curious about new tools and AI-powered SDLC practices.

Skills

Backend engineering

Distributed systems

Cloud architecture

English proficiency

Ownership mindset

Education

B.Sc. in Computer Science or equivalent

Tools

Node.js

GraphQL

Neo4j

Kafka

Redis

AWS

Job description

AppsFlyer is known for its massive backend production. At any given moment thousands of servers are consuming 200+ billion mobile app events daily, crunching our users' data, serving requests, and communicating on a massive scale. To achieve such scale, our data & microservice architecture is built with the best and latest cutting-edge technologies such as Node.js, Go, Kafka, GraphQL, Neo4j, Redis, BigQuery, AWS, and many more…

The SaaSLab group is part of the AFOS (AppsFlyer Operating System) unit which owns the SaaS platform and control plane of AppsFlyer — the foundational layer that manages users, accounts, billing, API gateway, authentication, permissions, and business integrations. SaaSLab's systems serve as the backbone for every product and feature at AppsFlyer, handling millions of API calls daily and supporting thousands of enterprise customers worldwide.

We are looking for an exceptional Software Engineer to join the Domain Team within SaaSLab. The Domain Team owns AppsFlyer's core entities — accounts, apps, and users — as well as the onboarding experience. This is a foundational domain that every other product and team at AppsFlyer depends on. You will design, build, and operate the backend systems that power these entities while contributing to the team's ongoing architectural evolution.

The position requires strong backend engineering skills, a solid understanding of distributed systems, and the ability to take ownership of complex technical problems from design through production.

What You'll Do

• Design, develop, and maintain scalable backend systems and data flows for AppsFlyer's core entities (accounts, apps, users) and onboarding flows
• Take part in decoupling from legacy data stores, building a resilient domain model, and adopting modern patterns like GraphQL Federation
• Write high-quality, well-tested, production-grade code and take ownership of your features from design through deployment and operation
• Participate in architecture discussions, design reviews, and code reviews, contributing ideas and raising the bar for the team
• Collaborate closely with product managers, team leads, and engineers across SaaSLab and AFOS to define and deliver on the team roadmap
• Help ensure high availability, security, and operational excellence for systems that underpin every AppsFlyer product
• Troubleshoot, debug, and resolve production issues, contributing to on-call rotations as needed
• Stay curious about new tools, technologies, and approaches, and help the team adopt AI-powered tools and modern SDLC practices
• Contribute to a strong engineering culture of ownership, collaboration, quality, and continuous improvement

What You Have

• 5+ years of software development experience, with strong backend engineering skills
• Experience building and operating production-grade distributed systems
• Strong understanding of software design, system architecture, and development best practices
• Experience working with high-scale, cloud-based architectures
• Ability to take ownership of problems and drive them from design through production
• Excellent collaboration and communication skills, with experience working across multiple functions and stakeholders
• Strong sense of ownership and the ability to work with clarity in ambiguous spaces
• Proficiency in written and verbal English
• B.Sc. in Computer Science or equivalent practical experience

Bonus Points

• Experience with Domain-Driven Design (DDD) principles and practices
• Experience with SaaS platform systems — identity, access management, billing, multi-tenancy, API gateways, or similar control-plane domains
• Experience working on core entity systems, identity/account management, or SaaS onboarding flows
• Experience with Node.js, GraphQL, or graph databases (Neo4j)
• Experience with platform/infrastructure teams that serve internal engineering customers
• Experience in the ad-tech ecosystem, preferably with hyper-scale systems
• Recommended by an AppsFlyer employee

As a global company operating from 25 offices across 19 countries, we reflect the human mosaic of the diverse and multicultural world in which we live. We ensure equal opportunities for all of our employees and promote the recruitment of diverse talents to our global teams without consideration of race, gender, culture, or sexual orientation. We value and encourage curiosity, diversity, and innovation from all our employees, customers, and partners.

“As a Customer Obsessed company, we must first be Employee Obsessed. We need to make sure that we provide the team with the tools and resources they need to go All-In.” Oren Kaniel, CEO