Background
European Bank operated on a core banking system that had served it reliably for years but was never designed with modern digital services in mind. As European Bank looked to expand its digital offerings new customer-facing products, third-party integrations, and internal tooling every new initiative required a bespoke integration effort. Each connection to the core system had to be built, tested, and secured from scratch, with no shared standard to build on. This slowed delivery, increased the surface area for errors, and made it difficult for European Bank’s technology team to reason about what was actually connected to its most critical systems at any given time.
Gunpowder Innovations was brought in to design and build an integration layer that would solve this problem once, rather than solving it repeatedly for every future product.
Research & Discovery
Our team began with a structured discovery phase to understand European Bank’s existing infrastructure before proposing any technical solution. This wasn’t a surface-level audit we worked directly with European Bank’s engineering, operations, and compliance teams to map how data and transactions actually moved through the organization, not just how they were documented to move.
Key focus areas included:
Legacy system limitations Identifying which parts of the core banking system had documented APIs, which had none, and which relied on batch processes or manual intervention.
Integration point mapping Cataloguing every existing connection between the core system and external services, including undocumented or informal integrations built over time.
Security and compliance requirements Understanding the regulatory constraints around financial data exchange, including data residency, encryption standards, and audit requirements specific to European Bank’s jurisdiction.
Operational risk assessment: Evaluating where existing manual or semi-automated integration workflows created risk of error, delay, or inconsistent data.
Scalability requirements: Understanding European Bank’s product roadmap for the next 12–24 months, so the integration layer wouldn’t need to be redesigned for the next initiative.
Stakeholder alignment: Running structured sessions with both technical and business stakeholders to make sure the roadmap reflected operational reality, not just an engineering ideal.
This discovery phase took 5 weeks and produced a detailed technical and product roadmap, reviewed and signed off by European Bank’s technology leadership before any development began.
Integration Architecture & Design
Rather than building point-to-point connections for each new use case, we designed a dedicated integration layer that sits between European Bank’s core systems and any modern service that needs to consume them. This meant every future product would integrate against a single, well-documented interface instead of the core system itself.
Key architectural decisions included:
A standardized API layer over legacy core banking functions, translating older protocols and data formats into consistent, modern API contracts.
Clear separation of concerns between the core banking system and any consuming service, so a fault or change on either side wouldn’t cascade into the other.
Built-in authentication and authorization on every integration point, with granular permissioning so different consuming services only had access to the data and functions they specifically needed.
Comprehensive audit logging, capturing every request and response for compliance and troubleshooting purposes.
Versioned API contracts, so future changes to the integration layer wouldn’t break existing integrations without a clear, managed migration path.
Documentation-first delivery: every endpoint was documented before it was considered complete, so future teams (internal or Gunpowder) could integrate without needing to rediscover how the system worked.
We reviewed the architecture with European Bank’s security and compliance teams at each major milestone, rather than presenting it as a finished design at the end.
Development & Infrastructure Integration
With the architecture approved, our engineering team moved into building the integration layer itself, working in close coordination with European Bank’s internal infrastructure team to avoid disruption to live systems.
Key implementation areas:
Core banking API integration: Building the connective tissue between the new integration layer and European Bank’s existing core banking modules, account systems, and transaction processing.
Secure transaction handling: Ensuring every transaction passing through the new layer was encrypted in transit and at rest, with tamper-evident logging.
Scalable backend architecture: Designing the layer to handle significant increases in transaction volume without requiring architectural changes, using horizontal scaling and queue-based processing for high-throughput endpoints.
Performance optimization and monitoring: Instrumenting every endpoint with monitoring and alerting, so degraded performance or failures were caught before they affected end users.
Staged rollout: Deploying the integration layer incrementally against non-critical systems first, then progressively onto higher-stakes core functions as confidence in stability increased.
Rollback planning: Building rollback procedures for every deployment stage, so any issue could be reversed quickly without impacting live banking operations.
Technical Challenges & How We Solved Them
Legacy protocol translation: Several core banking modules communicated using older, proprietary protocols with limited documentation. We reverse-engineered the necessary interfaces through controlled testing in a sandboxed environment before touching production systems.
Zero-downtime requirement: European Bank could not accept downtime on core systems during integration. We designed the rollout to run the new integration layer in parallel with existing workflows, validating outputs matched before cutting traffic over.
Regulatory constraints on data handling: Certain data could not leave specific jurisdictions or environments. The architecture was designed with this in mind from the outset, rather than retrofitted afterward.
Key Features
Core Banking Connectivity: Integrated existing banking infrastructure with modern digital services and APIs, without requiring changes to the underlying core system.
Secure Financial Architecture: Built secure transaction workflows and data handling processes aligned with financial industry standards.
Scalable System Design: Designed infrastructure capable of supporting future fintech products and increasing user demand without architectural rework.
Reusable Integration Layer: Delivered a standardized connection point so future products no longer need custom, one-off integration work.
Audit & Compliance Logging: Every integration point logs activity in a tamper-evident format for regulatory and internal audit purposes.
Versioned API Contracts: Future changes to the integration layer can be rolled out without breaking existing consuming services.
Impact
The integration layer changed how European Bank’s technology team approached every subsequent product initiative. Instead of scoping and building a bespoke integration for each new product, teams could build against a stable, documented interface, cutting both the time and the risk involved in connecting to core systems.
Outcomes:
Faster onboarding of new digital products onto core systems, with integration timelines reduced from around 8 weeks to under 2 weeks per product
Reduced custom integration work per product launch, freeing internal engineering capacity for product-specific work
Enhanced scalability for future services, validated under 5x projected transaction volume in load testing
Modernised infrastructure with fintech-ready capabilities, positioning European Bank to launch future digital products faster
Stronger compliance posture through consistent, auditable integration across every connected service
Reduced operational risk, with fewer manual intervention points in day-to-day data flow
Client Feedback
“What used to take our team weeks of back-and-forth just to connect a new service to our core systems now takes days. Gunpowder didn’t just build an integration, they built us a way of integrating.”
Head of Digital Banking, European Bank
Conclusion
Gunpowder Innovations helped European Bank modernise how its core systems connect to the outside world, replacing one-off custom integrations with a secure, reusable architecture. By combining infrastructure strategy, security-first design, and scalable engineering, the project delivered a foundation that makes every future integration faster, safer, and lower-risk, turning what had been a recurring bottleneck into a solved problem European Bank’s team no longer has to think about.
