Senior Backend Engineer: Java, Kafka & Offline Deployments

ILIAS Solutions; Diegem; Hybrid; EUR 90,000 - 130,000; 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

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