Site Reliability Engineer - Senior

The opportunity

The Core Foundation & Integration Tribe (CFI) implements and delivers the Card Issuing core applications, from Card Issuing lifecycle to Transactions clearing & settlement to hundred of banks. With over 150 million cards and 1.16 billion monthly transactions, our platforms operate at the forefront of capacity and performance.

We are looking for an engineer to be the architect and guardian of our Card issuing solutions performance and reliability.

This is a strategic, hands-on engineering role for someone obsessed with making large-scale distributed systems fast, resilient, and efficient by design. You will be the technical cornerstone of our platform's stability, with the mandate to influence architecture, write code, and solve the most complex performance puzzles.

Day-to-day responsibilities

• Review critical solution designs and veto architectures that present unmitigated performance or reliability risks.
• Architect and operate our centralized performance and load testing platform, providing it as a self-service to our development squads.
• Design and lead our most critical end-to-end performance tests and Chaos Engineering to find system weaknesses before our customers do.
• Analyze long-term performance metrics (SLOs) to identify slow regressions and silent bottlenecks, and drive their resolution before they become incidents
• Lead war rooms for performance incidents, using advanced tools (profilers, distributed tracing) to diagnose systemic root causes.
• Recommend solution and prototype fixes, optimize critical code paths, and demonstrate the solution to development teams
• Liaise with the SRE and operations teams of our internal and external clients, building deep technical credibility.

Who are we looking for

We look for people who can drive positive change, step up and show what’s next – people with passion, can-do attitude and a hunger to learn and grow. In practice this means:

• 5+ years of proven experience with deep, hands-on expertise in a language like Java, or Python, legacy and public cloud (GCP, AWS) knowledge.
• You are obsessed with how large-scale distributed systems interact. You think in terms of concurrency, queuing, caching, consistency, and failure modes.
• Your expertise covers the full spectrum of modern communication patterns: from synchronous, high-throughput API-driven interactions, to decoupled and resilient event-driven architectures (Kafka), and the reliability of large-scale batch processing
• Crucially, you know precisely when to use each pattern to trade off speed, consistency, and throughput
• Expertise in technical domains : Application Performance Monitoring, Databasee performance optimization (Oracle, PostgreSQL), network analysis, low-level system performance
• Your arguments are backed by metrics, traces, and logs. Your motto is "Data over opinions." You are an expert in monitoring tools like Prometheus, Grafana, and distributed tracing
• You lead through your technical credibility and your ability to dive deep into the code to solve the most complex problems. This is not a PowerPoint-and-meetings role
• You excel at explaining complex technical concepts in simple terms and have a proven ability to mentor and influence senior engineers across multiple teams.
• You have a strong sense of ownership and accountability, with a bias for action and a focus on delivering measurable improvements in reliability and performance
• Full professional proficiency in English is required for our international environment.

Perks & Benefits

At Worldline you’ll get the chance to be at the heart of the global payments technology industry and shape how the world pays and gets paid. On top of that, you will also:

• Be part of a company guided by a strong purpose to do good and recognized as top 1% of the most sustainable companies in all sectors worldwide.
• Work with inspiring colleagues and be empowered to learn, grow and accelerate your career.