API & Middleware Integration

Your systems should behave like a well-run service: predictable outcomes, and the freedom to evolve without breaking everything else. We build open-source-first integration layers that turn complexity into capability - securely, transparently, and on your terms.

Whether you are bridging legacy platforms, enabling near real-time events, or standardising data across teams, we will design something bespoke that fits how you actually operate - and hand you the control to keep it moving.

What Is API & Middleware Integration?

API and middleware integration is how modern businesses connect applications so data and actions move automatically between systems. Instead of teams re-entering information or reconciling mismatched records, integrations create reliable pathways for information exchange - securely and in near real time.

  • APIs (Application Programming Interfaces) provide structured, controlled access to data and services between applications (for example, syncing customer updates from a CRM into billing).
  • Middleware sits between systems and manages orchestration, transformation, routing, and reliability - especially when workflows span multiple platforms, formats, or legacy tools.

Together, APIs and middleware form the backbone of automation: they reduce duplication, improve service responsiveness, and support consistent operations across departments and locations.

Platforms & Technologies We Work With

Non-exhaustive - depends on requirements.

  • API Design & Delivery

    REST, GraphQL, gRPC, OpenAPI/Swagger

  • Eventing & Messaging

    Kafka, RabbitMQ, NATS

  • API Gateways & Edge

    Kong, NGINX, Traefik, Envoy, Caddy

  • Identity & Security

    OAuth2, OIDC, Keycloak, JWT, mTLS

  • Data & Transformation

    JSON, XML, CSV, XSLT, schema validation, mapping pipelines

  • Observability & Reliability

    Prometheus, Grafana, ELK/OpenSearch, OpenTelemetry

When Systems Don't Line Up

Integration projects often stall when critical systems were never designed to cooperate: legacy interfaces behave unpredictably, data meaning differs between platforms, and operational workflows depend on manual checks to prevent costly mistakes. The result is fragile automation, inconsistent reporting, and change that feels riskier than it should.

We tackle this by designing an integration layer that matches your real-world workflows, not vendor diagrams: we define canonical data models, implement transformation and validation where it actually matters, and choose the right patterns (API-led, event-driven, or orchestrated middleware) to balance speed, resilience, and governance. Every integration is built with security, observability, and safe change built in from day one.

Legacy Interfaces

Ageing platforms expose limited or inconsistent endpoints and behaviours. We wrap them with adapters and stable contracts, then modernise safely without forcing a full rewrite.

Conflicting Data Definitions

The same entity is represented differently across systems, creating mismatches downstream. We establish a clear canonical model with mapping, validation, and reconciliation rules.

Human-Driven Handoffs

Key steps rely on people to move data between tools, increasing delay and error rates. We orchestrate end-to-end flows so actions trigger automatically with auditability.

Growth and Change Pressure

Point-to-point links multiply and become brittle as volume and complexity rise. We implement scalable patterns and clear boundaries that make new connections predictable.

Integration Built Around Your World

API and middleware integration delivers the most value when aligned to real operational workflows - billing, provisioning, fulfilment, scheduling, compliance, and support. We build integrations that reduce friction across teams while improving reliability and scale.

Telecoms

Automate provisioning, billing triggers, and service lifecycle actions to reduce delays and improve customer response times.

E-commerce

Keep inventory, orders, payments, and customer data synchronised across platforms for accurate fulfilment and smoother shopping journeys.

Healthcare

Enable secure, auditable data exchange between clinical and admin systems while supporting compliance requirements.

Education

Connect student systems, learning platforms, and admin tools to simplify enrolment, reporting, and operational workflows.

Logistics

Integrate fleet, shipment, and warehouse systems to improve visibility, reduce delays, and support real-time coordination.

Manufacturing

Link production, supply chain, and sales systems to minimise downtime, improve forecasting, and maintain consistent data flows.

Built for Change, Designed for Control

Our integration services are designed to be dependable today and adaptable tomorrow. We focus on clarity, stability, and operational control - so integrations don't become fragile dependencies.

From Discovery to Go-Live, Done Properly

We don't “just connect systems.” We design integration as an operational capability - documented, supportable, and built to evolve as your business changes.

  • 1

    Discovery & Technical Due Diligence

    We run structured workshops with technical and operational stakeholders to map systems, workflows, data ownership, and failure points. You get a clear view of constraints, risks, and a recommended integration approach that matches how you actually operate.

  • 2

    Solution Blueprint & Delivery Plan

    We design the target architecture and choose the right patterns (API-led, event-driven, or orchestrated middleware) with security and governance built in. We also define data contracts, testing strategy, environments, and a staged rollout plan with clear milestones.

  • 3

    Build, Test & Release

    We develop APIs, connectors, middleware routes, and automation logic with version control, repeatable deployments, and peer review. We validate behaviour in staging, prove resilience and performance, then release with controlled cutovers to minimise disruption.

  • 4

    Handover, Training & Ongoing Options

    We provide documentation, runbooks, and practical training so your team can operate and extend the integration with confidence. If you want us on hand, we agree support pathways that fit your operating model, from ad-hoc help to fully defined support coverage.

Why Choose OnyxSis?

Open-Source Craft, Done Seriously

We are an open-source-first engineering team that values clarity, quality, and long-term maintainability over quick fixes. Our work is built to be understood, owned, and evolved - by you, not locked behind us.

A Team That Treats Complexity as the Job

We take on difficult integration challenges because that is where thoughtful engineering delivers the biggest impact. You will work directly with people who listen carefully, communicate transparently, and stay accountable to outcomes.

Evidence That It Works in the Real World

In our Issue Diagnosis & Evaluation Suite case study, we built a unified diagnostic platform for a UK telecoms provider to eliminate fragmentation across back-end systems. The solution enabled multi-system diagnostics and automated discrepancy correction across previously disconnected tools.

The results were measurable: a 61% increase in first-contact resolutions and a 24% uplift in successful subscription provisioning. It is a strong example of how disciplined integration can improve operational performance, not just technical architecture.

Support That Stays With You

After go-live, we stay available to keep integrations stable, monitored, and improving as priorities evolve.

For guaranteed coverage and clear response expectations, we offer SLA-Based Technical Support, and for hands-on engineering help, Dedicated Support Hours provides access to the team that built the solution.

When you're ready to reduce manual effort, improve data confidence, and make change easier, we'll meet you and help teams trust integration.

Talk to Our Team

Frequently Asked Questions

Still have questions? Contact us - our team is here to help.

From Friction to Flow

When data definitions clash and handoffs slow teams down, we design APIs and middleware that make automation consistent, auditable, and resilient.

Plan Your Integration