Senior Java Engineer at La Fosse Associates, London, £400 per day

We're currently working with our client to seek an Integration Engineer to design and build the middleware layer connecting Shopify with enterprise backend systems such as OMS, ERP, and WMS. This role focuses on technical integration and data flow rather than front-end or theme development. You’ll work closely with their backend engineers (primarily Java-based) to ensure robust, scalable, and observable data exchange between Shopify and other platforms.

This is a 6+ month contract position paying £400 per day outside IR35 with 3 days onsite in Paddington, London

Responsibilities:

• Develop and maintain custom Shopify app logic and middleware services for system-to-system integration.
• Design and implement data flows using REST/GraphQL APIs, webhooks, and event-driven patterns (e.g. Kafka).
• Define and manage data contracts, schema mappings, and transformation logic between Shopify and backend systems.
• Collaborate with backend engineers to design integration endpoints, manage authentication, and handle errors.
• Implement observability and monitoring for integration APIs (using tools like Dynatrace, New Relic, or Azure Monitor).
• Troubleshoot and optimise data exchange processes across multiple systems.
• Support testing, validation, and refinement of end-to-end integration flows.

Experience required:

• Focus: Architecture, API design, mentoring, delivery - Shopify experience
• Core Skills: Backend Development (Micronaut preferred): Java, Gradle, REST & Kafka scaffolding, Health checks
• API Design & Integration: OpenAPI / AsyncAPI specs, Shopify integration patterns
• Testing & Quality: Unit tests, code coverage, mocking strategie, Contract testing, test data generation
• Architecture & Patterns: Domain-driven design, event-driven architecture, Reusable components (e.g., Catalogue Validator)
• Dev Standards & Governance: Linting, formatting, secure coding practices.