Senior Java Developer

Callisto Web Solutions B.V.; Amsterdam; On-site; EUR 90,000 - 130,000; Full time

Job summary

Callisto Web Solutions B.V. is seeking an experienced Senior Java & Azure Cloud Engineer to design and implement scalable, secure, cloud-native solutions.

You will work across the full project lifecycle, collaborating with clients and multidisciplinary teams to translate business requirements into robust technical designs. You will lead microservices architectures using Java 17/21, Spring Boot 3, Docker, Kubernetes, AKS, and event-driven patterns with Kafka and Azure Event Hubs.

Qualifications

• Extensive hands-on experience with Java 17/21 and Spring Boot 3.
• Proven ability to design microservices and distributed systems.
• Practical knowledge of Kafka or Azure Event Hubs.
• Experience with Docker, Kubernetes, and AKS.
• Knowledge of cloud security, RBAC, and compliant deployments.
• Strong collaboration and communication with clients and teams.

Responsibilities

• Design, plan, and implement microservices-based architectures across the lifecycle.
• Develop scalable apps with Java 17/21 and Spring Boot 3.
• Implement event-driven patterns using Kafka and Azure Event Hubs.
• Ensure secure apps with OAuth2/JWT and Spring Security.
• Work with SQL and NoSQL databases including Cosmos DB.
• Tune JVM performance and conduct profiling.
• Create unit and integration tests with Mockito and Testcontainers.
• Build and manage Docker containers and Kubernetes deployments.
• Set up CI/CD pipelines and IaC using Terraform or Bicep.
• Design and maintain Azure infrastructure and monitoring (Azure Monitor, Grafana).

Skills

Java

Spring Framework

Microservices

CI/CD

DevOps

Cloud security

Tools

Kafka

Azure Event Hubs

AKS

Docker

Kubernetes

Terraform

Bicep

Prometheus

Grafana

Azure Monitor

Mockito

Testcontainers

Rest Assured

Job description

We are looking for an experienced Senior Java & Azure Cloud Engineer to design and implement scalable, secure, and high-performing cloud-native solutions.

In this role, you will work across the full project lifecycle, from architecture and planning through implementation and optimisation. You will collaborate closely with clients and multidisciplinary teams to translate business requirements into robust technical solutions.

Key Responsibilities

• Design, plan, and implement microservices-based architectures across the full software development lifecycle.
• Develop scalable and maintainable applications using Java 17/21 and Spring Boot 3.
• Design and implement event-driven architectures using technologies such as Kafka and Azure Event Hubs.
• Develop secure applications using OAuth2, JWT, and Spring Security.
• Work with both SQL and NoSQL databases, including Azure Cosmos DB.
• Analyse and optimise application performance through JVM configuration, profiling, garbage collection, and performance tuning, including the use of JMeter.
• Develop and maintain comprehensive unit and integration testing using tools such as Mockito, Testcontainers, Rest Assured, and Cloud Contract.
• Build and manage containerised applications using Docker and Kubernetes, with a preference for Azure Kubernetes Service (AKS).
• Implement and maintain CI/CD pipelines and cloud-native deployment practices.
• Design and manage Azure infrastructure using Infrastructure as Code (Bicep/Terraform).
• Implement and maintain Azure security practices, including Identity Management, RBAC, and compliance.
• Develop monitoring and observability solutions using Azure Monitor, Prometheus, and Grafana.
• Identify opportunities to improve resource utilisation, performance, scalability, and cost efficiency.
• Stay up to date with emerging technologies and contribute to continuous technical improvement.

Required Expertise

• Extensive professional experience with Java 17 and/or Java 21.
• Strong experience with Spring Boot 3 and the Spring ecosystem, including Spring Core, Spring Security, Spring JPA, Transactions, and AOP.
• Strong understanding of microservices and distributed systems.
• Experience with SQL and NoSQL databases, preferably Cosmos DB.
• Hands-on experience with JVM performance tuning and memory management.
• Experience with OAuth2 and JWT.
• Practical experience with Kafka and/or Azure Event Hubs.
• Strong experience with Docker and Kubernetes, preferably AKS.
• Solid knowledge of Microsoft Azure, including Key Vault, Storage, VMs, Networking, and related services.
• Experience with Terraform and/or Bicep.
• Knowledge of cloud security, identity management, RBAC, and compliance.
• Experience with Azure monitoring, Prometheus, and Grafana.
• Strong understanding of CI/CD and DevOps practices.
• Excellent problem-solving, communication, and collaboration skills.
• Ability to work effectively with clients and multicultural, multidisciplinary teams.