Senior Software Engineer, Backend at Flex in San Francisco, CA

Summary: Flex is a growth-stage FinTech company headquartered in NYC that aims to enhance the rent payment experience. They are seeking a Senior Backend Engineer to design, build, and scale backend services and APIs while collaborating with cross-functional teams to deliver robust systems that impact renters and partners. Responsibilities: - Design, develop, test, and scale backend services and APIs that power Flex’s consumer products, partner integrations, risk management systems, and core platform services - Build and operate robust, fault-tolerant distributed systems with multiple external dependencies - Implement service APIs for web and mobile apps, simplifying complex rent payment processing - Work closely with Product, Design, Infrastructure, Sales, Partner, and Customer Success to deliver features and integrations that delight customers and partners - Translate feature requirements into technical specifications and lead the architecture and implementation of scalable solutions - Drive the full lifecycle of services and APIs you build, including deployment, monitoring, and optimization for high availability and performance - Contribute to evolving Flex’s service-oriented architecture, REST APIs, message queues, and scalable systems design - Develop risk management systems such as rules engines, ML-powered fraud detection, and high-scale event ingestion pipelines - Mentor junior engineers and help elevate the team’s engineering practices through code reviews, architecture discussions, and technical leadership - Ensure services are observable and reliable using monitoring tools and industry best practices - Collaborate on CI/CD improvements and automation to increase code quality and delivery velocity Required Qualifications: - A minimum of 4 years of experience with Java is required for this position - Strong computer science fundamentals with a proven track record of building scalable backend systems - 5–6+ years of professional software engineering experience with a focus on backend development - 4+ years of hands-on Java experience, with deep knowledge of the Java ecosystem - Proficient in Java frameworks and tools used at Flex: Spring (core/web/boot), Gradle, JUnit, JVM tuning and performance optimization - Experience operating services in distributed, service-oriented architectures at scale - Familiarity with REST API design, mobile API best practices, and message-driven architectures - Skilled at building robust, fault-tolerant systems and integrating with multiple external dependencies - Experience designing and maintaining data pipelines and working with big data platforms (bonus: Snowflake) - Hands-on experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB), containerization (Docker/Kubernetes), and Infrastructure as Code (CDK/Terraform) - Skilled in observability and monitoring tools (e.g., DataDog) to ensure high availability - Ability to write high-quality code that is testable, maintainable, scalable, and secure, using industry best practices throughout the SDLC (unit testing, build automation, CI/CD) - Excellent communicator, comfortable working with distributed teams and cross-functional stakeholders - Proven ability to mentor junior engineers and raise the technical bar through best practices Preferred Qualifications: - Experience in risk engineering, rules engine architecture, and implementing risk/fraud/credit policies in production systems is highly valued Required Skills: Java, Spring Framework, Gradle, JUnit, JVM tuning, performance optimization, Distributed systems, Service-oriented architecture, REST API design, Message-driven architecture, Data pipelines, Big data platforms, AWS, EKS, Aurora RDS, Elasticache, DynamoDB, Docker, Kubernetes, Infrastructure as Code, CDK, Terraform, Monitoring tools, DataDog, Unit testing, Build automation, CI/CD, Risk engineering, Rules engine architecture, Fraud detection, Credit policies, Machine learning Benefits: Competitive medical, dental, and vision, Company equity, 401(k) plan with company match, Unlimited paid time off + 13 company paid holidays, Parental leave, Flex Cares Program: Non-profit company match + pet adoption coverage, Free Flex subscription