Senior Backend Engineer | Java

ILIAS Solutions; Diegem; Hybrid; EUR 90,000 - 125,000; Full time

Benefits offered by this job

Security-clearance support

Hybrid work model (2 days on-site)

Job summary

ILIAS Solutions in Diegem, Belgium, is seeking a senior backend engineer to design and maintain Java backend services and APIs for offline, air-gapped NATO environments. You will influence coding standards, guide architecture, and mentor engineers across the Backend Engineers chapter, with a focus on stability, versioning, and reproducible deployments.

You will work across REST, SOAP, batch, Kafka, Kubernetes packaging, and security practices, collaborating with product owners and analytics

Qualifications

• 6+ years of professional backend engineering experience with Java as your primary language.
• Expert-level Java 17+ with deep knowledge of Spring Boot or Quarkus, and strong JVM internals: garbage collection tuning, memory profiling, heap and thread dump analysis.
• Production Kafka experience at depth: producers, consumers, idempotency handling and schema evolution, not familiarity, but real operational ownership.
• REST API design with OpenAPI, including versioning strategy and backward compatibility across release cycles; strong JPA/Hibernate, JDBC and database migration tooling (Flyway or Liquibase); PostgreSQL query optimisation, indexing, partitioning and large-table migrations.
• Docker, Kubernetes and Helm in production packaging contexts, not only local development; CI/CD pipelines (Jenkins or GitHub Actions); security and quality tooling including SonarQube, dependency scanning, SBOMs and image signing used in a real delivery pipeline.
• OIDC and Keycloak at the integration and usage level for authentication and authorisation; secrets management, TLS and RBAC; structured logging, metrics and observability tooling (Grafana, OpenSearch or equivalent).
• Clear written and verbal communication in English with both engineering and product stakeholders; a degree in computer science or software engineering, or equivalent professional experience that demonstrates the same capability.
• Eligibility to obtain and maintain the required national or NATO security clearance for this role (we support candidates through the clearance process).

Responsibilities

• Design and maintain Java backend services and APIs so they remain stable and versioned across releases, allowing customers in offline environments to upgrade on their own schedule.
• Build and own complex business logic and integration layers connecting to legacy and customer systems, working across REST, SOAP, batch file exchange and event-driven patterns with Kafka.
• Package and deliver services for Kubernetes deployments including offline customer installations, applying reproducible build, image signing and SBOM practices throughout.
• Define and embed Java coding standards, dependency policies, security defaults and testing practices across the chapter, reducing bus-factor risk through shared ownership.
• Contribute to build-or-not decisions alongside product owners, translating technical constraints and integration complexity into options the product team can act on.
• Collaborate with analytics engineers on Python and Spark integrations, and review technical design documents to raise the quality bar across the team.

Skills

Java backend

Spring Boot / Quarkus

Kafka

OpenAPI REST design

Docker / Kubernetes

CI/CD pipelines

SBOM tooling

English communication

NATO security clearance eligibility

Education

Degree in Computer Science or Software Engineering

Tools

Jenkins

GitHub Actions

Flyway or Liquibase

PostgreSQL

Grafana/OpenSearch

Keycloak

SonarQube

Job description

Opportunity

Hybrid (2 days on-site) · Permanent, full-timeAbout the roleOffline, air-gapped installations for NATO customers mean yourAPI versioning and backward-compatibility decisions are not technical hygiene, they are the difference between a fleet that can operate and one that cannot. The backend services you design and maintain run in constrained, version-locked environments where an incompatible release cannot simply be rolled back over a network connection. Beyond feature delivery, this role carries real technical leadership weight: you will help set Java coding standards, guide architectural decisions, and mentor engineers across the Backend Engineers chapter, with an explicit goal of distributing knowledge rather than concentrating it.

Your Mission

What you'll do

• Design and maintain Java backend services and APIs so they remain stable and versioned across releases, allowing customers in offline environments to upgrade on their own schedule.
• Build and own complex business logic and integration layers connecting to legacy and customer systems, working across REST, SOAP, batch file exchange and event-driven patterns with Kafka.
• Package and deliver services for Kubernetes deployments including offline customer installations, applying reproducible build, image signing and SBOM practices throughout.
• Define and embed Java coding standards, dependency policies, security defaults and testing practices across the chapter, reducing bus-factor risk through shared ownership.
• Contribute to build-or-not decisions alongside product owners, translating technical constraints and integration complexity into options the product team can act on.
• Collaborate with analytics engineers on Python and Spark integrations, and review technical design documents to raise the quality bar across the team.

What success looks likeOver time, the backend services you own become the most dependable part of the platform: APIs hold their contracts across releases, new engineers can read and extend the codebase without escalating to you, and offline deployments ship with a clear, reproducible packaging trail. As your ownership grows, the chapter's standards documents reflect decisions you have driven and stress-tested with domain experts, and build-or-not conversations happen earlier because the team trusts your technical reading of complexity and risk.

What you bring

• 6+ years of professional backend engineering experience with Java as your primary language, and a solid track record across complex, production-grade systems.
• Expert-level Java 17+ with deep knowledge of Spring Boot or Quarkus, and strong JVM internals: garbage collection tuning, memory profiling, heap and thread dump analysis.
• Production Kafka experience at depth: producers, consumers, idempotency handling and schema evolution, not familiarity, but real operational ownership.
• REST API design with OpenAPI, including versioning strategy and backward compatibility across release cycles; strong JPA/Hibernate, JDBC and database migration tooling (Flyway or Liquibase); PostgreSQL query optimisation, indexing, partitioning and large-table migrations.
• Docker, Kubernetes and Helm in production packaging contexts, not only local development; CI/CD pipelines (Jenkins or GitHub Actions); security and quality tooling including SonarQube, dependency scanning, SBOMs and image signing used in a real delivery pipeline.
• OIDC and Keycloak at the integration and usage level for authentication and authorisation; secrets management, TLS and RBAC; structured logging, metrics and observability tooling (Grafana, OpenSearch or equivalent).
• Clear written and verbal communication in English with both engineering and product stakeholders; a degree in computer science or software engineering, or equivalent professional experience that demonstrates the same capability.
• Eligibility to obtain and maintain the required national orNATO security clearance for this role(we support candidates through the clearance process).

If you meet most of these criteria, we encourage you to apply. The eligibility requirement for the required security clearance is not flexible.

Nice to have

• Legacy integration depth: Oracle, SQL Server, PL/SQL, SOAP or batch file exchange in production contexts.
• Air-gapped or offline software delivery experience, particularly using signed bundles or tooling such as Zarf; experience with FIPS mode or STIG-hardened environments is especially relevant given our deployment constraints.
• Advanced Keycloak administration and fine-grained authorisation configuration; reactive or async Java patterns using virtual threads or Project Reactor.
• Experience in regulated or defence-adjacent industries; working knowledge of Dutch or French.

Build Your Future with ILIAS

Why ILIAS SolutionsILIAS Solutions is part of the Patria Group and builds software that defence operators depend on to plan and execute missions. The platform runs in the environments where failure is not recoverable with a hotfix: offline, air-gapped, version-locked. That context makes correctness and compatibility genuinely consequential, and it makes the engineering choices here matter beyond the sprint.This is a role for an engineer who finds legacy integration intellectually interesting rather than career-limiting, who wants to set standards rather than just meet them, and who values a codebase they can be proud of over one they are the only person who understands. The working language is English; Dutch or French is useful but not required to do the job well.EligibilityBecause of the nature of our work, this role may require eligibility under applicable export-control regulations and the ability to obtain national or NATO security clearance. We assess eligibility lawfully and on a role-by-role basis; specific requirements are discussed during the selection process. We do not exclude candidates on the basis of nationality except where mandated by applicable export-control or security-clearance law.