Backend Developer (Java)

Rakuten Viber; Warszawa; Hybrid; PLN 180,000 - 320,000; Full time

Job summary

Rakuten Viber, Warsaw-based, is seeking a Backend Developer to build and maintain high-traffic Java services. You will design scalable, low-latency systems, work on microservices in a cloud environment, and ensure security and performance across a billion daily messages.

The role requires 4+ years in backend development, strong Java expertise, and experience with Docker/Kubernetes, NoSQL databases and Agile practices. Hybrid work is available with in-office presence required several days a week.

Qualifications

• At least 4 years of Backend Development experience with Java.
• Experience with Async/Reactive Java frameworks (e.g., Vert.x, RxJava, Akka).
• Experience with NoSQL databases (e.g., Couchbase, MongoDB).
• Hands-on with Docker and Kubernetes in microservices.
• Knowledge of cloud technologies.
• Experience with unit testing and mocking frameworks.
• Familiarity with Agile methodologies.
• Fluent in written and spoken English.

Responsibilities

• Plan, design, and develop Java high-availability, low-latency applications.
• Define objectives and functionality for services.
• Ensure designs align with business goals and architecture.
• Contribute to architectural reviews and continuous improvement.
• Collaborate with Product and Architects on mission-critical systems.

Skills

Java

Async/Reactive Java

NoSQL databases

Docker & Kubernetes

Cloud technologies

Unit testing

Agile methodologies

English communication

AI tools for productivity

Microservices

Education

Higher technical education

Job description

Rakuten Viber is one of the most popular and downloaded apps in the world. Working with us provides a unique opportunity to influence hundreds of millions of our users and to be part of the journey that makes us a super-app. Our mission is to make people’s lives easier by enabling meaningful connections, from precious moments with family and friends, through managing business relationships to pursuing their passions.

We are a global team of engineers dedicated to creating the best tools to ensure safe, convenient, and fun communication for millions of users worldwide. Our culture is built on innovation, teamwork, and a commitment to excellence. We offer a unique opportunity to work with cutting-edge technologies, including microservices architecture, and influence the lives of millions of people.

As a Backend Developer at Viber, you will be involved in developing and maintaining high-traffic with over 1 billion messages a day and dozens of scalable services, ensuring the fast and reliable operation of our platform. Your tasks will include developing new features, optimizing performance, ensuring data security, and solving complex technical challenges within our microservices architecture, using a combination of Java, along with non-blocking and reactive approaches, Cloud services, and NoSQL databases.

Responsibilities

• Planning, designing, developing and maintaining Java high-availability applications that can be high-volume and low-latency.
• Define application objectives and functionality.
• Ensure application designs conform with business goals.
• Support continuous improvement, investigating alternatives and technologies, and presenting for architectural review.
• Work in a highly motivated team, closely with Product and Architects teams on large mission-critical systems.

Requirements

• At least 4 years of experience as a Backend Developer, with at least 2 years in Java.
• Advanced knowledge of Java, from frameworks to libraries. Experience in Async and/or reactive Java frameworks (such as Vertx, Rxjava, Akka).
• Advanced knowledge of unit testing frameworks and mocking.
• Knowledge of cloud technologies.
• Experience with using AI tools to increase productivity and quality.
• Experience with large scale NoSQL database (such as Couchbase, MongoDB).
• Experience with microservices development based on Docker and Kubernetes.
• Experience with Agile methodology.
• Striving for new knowledge and skill improvement.
• Fluent in written and spoken English (interviews are in English).
• Excellent oral and written communication skills.
• Higher technical education.
• Availability to work in a hybrid model - at least 3 days a week from the office.

Advantages

• Knowledge of Javascript and web ui technologies
• Experience with other server-side languages such as Python.
• Experience working with remote teams.