Jobs Java

Workload: full-time, remote
Start: asap
Duration: long-term
Location: any
English: B2

Technical requirements (general)
- 3+ years of production blockchain experience in BTC. Multi-protocol experience (strongly preferred).
- Java + Spring Boot + SQL
- Familiarity with test-driven development (TDD) and/or behaviour-driven development (BDD) as working practices, writing tests before or alongside implementation.
- Familiarity with Domain-Driven Design principles.
- Comfortable working in a monorepo structure with shared libraries, cross-squad code visibility, and coordinated CI/CD pipelines.
- Proactive communication, raising blockers, design concerns, and cross-squad dependencies.
- Written and verbal communication in English must be at a professional level.

Technical requirements (specific)
- Deep Bitcoin protocol expertise: PSBT format (BIP-174 and subsequent updates), UTXO management and coin selection algorithms, SegWit transaction structures, script types and descriptor formats (Taproot out of scope).
- Multi-signature coordination: BIP-48 (multi-sig derivation paths), BIP-67 (lexicographic key sorting), P2WSH script construction, PSBT combination and finalisation workflows.
- Fee estimation: Mempool analysis, RBF (Replace-By-Fee) and CPFP (Child-Pays-For-Parent) fee bumping strategies, fee rate prediction.
- Transaction construction: Witness data assembly, BIP-143 (SegWit sighash), DER signature encoding, low-S enforcement. Familiarity with sighash types. SIGHASH_ALL is the production default for custody; engineers should understand the full sighash taxonomy for validation and edge-case handling but implementation focuses on SIGHASH_ALL.
- Transaction lifecycle and remediation: Stuck transaction detection via mempool monitoring, RBF and CPFP execution for fee bumping, handling transactions that remain unconfirmed for extended periods, and managing the operational decision of when to replace vs wait.
- UTXO indexing and balance management: Experience with UTXO set tracking, balance computation from unspent outputs, UTXO consolidation strategies during low-fee windows, and address-level balance monitoring for deposit detection.
- Address management: Gap limit handling for HD wallets, change address allocation from internal derivation branch (m/84'/0'/0'/1/*), address reuse prevention, and descriptor-based address discovery for wallet import and recovery scenarios.
- Chain semantics and failure modes: Understanding of Bitcoin's probabilistic finality (confirmation depth vs settlement assurance), dust output limits and their implications for UTXO management, fee spike behaviour during congestion events (e.g. ordinals, inscription surges filling blocks for extended periods), double-spend detection for unconfirmed transactions, and the operational difference between a transaction that is "broadcast" vs "in mempool" vs "confirmed at depth N." Engineers must understand that Bitcoin has no concept of a "failed" transaction that consumes fees; a transaction either confirms or it doesn't, and unconfirmed transactions can be replaced or may eventually confirm unexpectedly.
- Production experience: Operating Bitcoin custody or wallet infrastructure at institutional scale, not testnet-only or personal wallet experience.

Candidate's responsibilities
Bitcoin wallet management, UTXO handling, transaction construction (PSBT, SegWit), multi-signature coordination, fee estimation.

About Flamingo

Flamingo is revolutionizing the Managed Service Provider (MSP) industry with an AI-driven, open-source platform for IT and security. Our goal is to empower MSPs with automation, optimization, and scalability tools to enhance their operations. 

Role Overview

As a Senior Back-end Engineer (Java) at Flamingo, you will design and develop scalable, high-performance back-end services and APIs using Java and Spring Boot. You will be responsible for implementing event-driven microservices, optimizing system performance, and ensuring high availability as we scale our platform. Your expertise in processing high-volume logs and integrating multiple data sources will be critical to building a robust and efficient system.

Key Responsibilities

• Design and develop scalable backend services and APIs using Java (Spring Boot).
• Architect and implement event-driven microservices with Kafka and RabbitMQ.
• Process and analyze high-volume logs efficiently to ensure scalability and real-time insights.
• Integrate and manage multiple data sources, including SQL, NoSQL, and streaming data.
• Optimize database performance using PostgreSQL, Redis, and Elasticsearch.
• Implement authentication and authorization mechanisms with OAuth, JWT, and Keycloak.
• Collaborate with front-end and DevOps teams to build a seamless and resilient system.
• Ensure code quality through automated testing, CI/CD pipelines, and best engineering practices.

Qualifications

Must-Have:

• 5+ years of experience in backend development with Java and Spring Boot.
• Experience in microservices architecture, including event-driven systems (Kafka, RabbitMQ).
• Strong knowledge of RESTful APIs, GraphQL, and WebSockets.
• Experience processing high-volume logs and working with log management tools (ELK stack, Loki, Fluentd, OpenTelemetry).
• Experience working with multiple data sources, including relational (PostgreSQL) and non-relational (Redis, Elasticsearch) databases
• Experience with containerization (Docker, Kubernetes) and cloud platforms (AWS/GCP).
• Understanding of security best practices in backend development.

Nice-to-Have:

• Experience with functional programming in Java or Scala.
• Familiarity with distributed tracing (e.g., Jaeger, Zipkin) for microservices.
• Knowledge of cloud-native architectures and serverless frameworks.
• Exposure to message queues and event sourcing.

Why Join Flamingo?

• High-impact role: As a back-end engineer, your contributions will directly shape Flamingo’s product and technology.
• Innovative Tech Stack: Work with cutting-edge open-source technologies in AI, automation, and security.
• Remote-first Culture: Flexibility to work from anywhere while collaborating with a top-tier team.
• Mission-Driven Company: Join a team passionate about disrupting the MSP industry and making enterprise-grade security and IT automation accessible to all.

🚀 AIMPROSOFT is looking for a Full-Stack Java Developer (ReactJS/Spring Boot)! 

Aimprosoft, a fast-growing IT company, is looking for a Full-Stack Java Developer (ReactJS/Spring Boot) on a contract basis (≈ 2+ months) for an international Telecom project. 

This is a hands-on backend role focused on building a Service Integration Layer for a UK broadband and telecom wholesale operator. The platform will orchestrate VOIP and hardware service fulfilment between the client’s commercial order management system and downstream suppliers. 

You will join the project at the MVP stage and contribute to an intensive 8-week Phase 0 proof of capability. The role is a strong fit for an engineer who is comfortable working with backend integrations, long-running workflows, AWS services, and evolving technical specifications. 

🎯 About the project & role: 

The Service Integration Layer will manage complex order journeys across the client’s wholesale carrier ecosystem. Its responsibilities include service qualification, VOIP ordering, supplier orchestration, inventory updates, status tracking, and reliable recovery of interrupted processes. 

You will: 

• Implement Service Qualification and Service Order APIs using Java and Spring Boot  
• Build an adapter for integration with an external VOIP and hardware supplier  
• Implement six supplier operations covering customer, subscription, user, and phone-number provisioning  
• Embed and configure a workflow engine such as Camunda, Flowable, jBPM, or a similar solution  
• Implement long-running workflows with timers, persisted state, retries, compensation, and recovery  
• Ensure reliable asynchronous processing through idempotency, correlation IDs, timeouts, and error handling  
• Build mocks and stubs for external systems to keep development independent of third-party sandbox availability  
• Implement a minimum read-only Service Inventory and catalogue configuration  
• Produce OpenAPI documentation and maintain a clear variance log for differences between the specification and implemented contracts  
• Demonstrate durable order persistence and clean workflow recovery after an intentional mid-process restart  
• Collaborate with the Architect, QA, DevOps, and Project Manager throughout implementation  

All development will take place inside the client’s AWS account, repositories, and CI/CD environment.  

🔥 What We Need From You: 

• 5+ years of commercial Java development experience  
• Strong hands-on experience with Spring Boot 
• Commercial experience with ReactJS and the ability to develop and maintain frontend components integrated with Java/Spring Boot APIs 
• Upper-Intermediate+ (B2+) English level 
• Experience building REST APIs and integration-heavy backend services  
• Solid understanding of REST and JSON API design and consumption 
• Experience integrating with at least one non-trivial third-party API  
• Practical knowledge of retry strategies, timeout handling, error processing, and idempotency  
• Experience with long-running or stateful business processes using workflow engines, sagas, or state machines  
• Understanding of asynchronous and event-driven integration patterns  
• Experience with microservice architecture  
• Familiarity with OAuth2-secured APIs  
• Practical AWS experience, particularly with services such as API Gateway, ECS/Fargate, Lambda, AWS OpenSearch, RDS, SQS, or EventBridge. 
• Basic understanding of infrastructure managed with Terraform  
• Ability to work effectively with evolving specifications, identify ambiguities, and raise them as tracked risks  

• Ability to deliver in a fast-paced, fixed-deadline environment  

   

📌 Nice to have: 

• Experience with TM Forum Open APIs  
• Background in telecom OSS/BSS integrations 
• Hands-on experience with Camunda 8 SaaS, Flowable, jBPM, or another BPM/workflow engine  
• Experience embedding or operating a workflow engine as part of a Java application  
• Understanding of process definitions, timers, compensation, and workflow state persistence  
• Understanding of telecom order lifecycle, service qualification, inventory, or provisioning processes  
• Experience with transactional outbox, idempotent consumers, correlation IDs, and recovery patterns  
• Experience working with Apache Kafka or RabbitMQ  
• Knowledge of AWS Secrets Manager  
• Experience working on fixed-scope or fixed-deadline delivery projects  
• Experience producing OpenAPI documentation and supporting Postman-based integration testing  
• Bachelor’s or Master’s degree in Computer Science or a related field  

💼 What We Offer: 

• Official military deferment (reservation); 
• A competitive salary that appreciates your skills and experience; 
• Opportunity to join a strategically important pilot team with long-term project prospects 
• Work on modern cloud-native products that deliver real-world impact 
• Exposure to AI-powered development practices and enterprise-scale engineering 
• Open environment where your ideas, technical expertise are valued 

PLEASE NOTE that we are searching for candidates who are located in Lviv and are able to visit office in Lviv.

About us:

EveryMatrix is a leading B2B SaaS provider delivering iGaming software, content and services. We provide casino, sports betting, platform and payments, and affiliate management to 200 customers worldwide.

But that's not all! We're not just about numbers, we're about people. With a team of over 1000 passionate individuals spread across twelve countries in Europe, Asia, and the US, we're all united by our love for innovation and teamwork.

EveryMatrix is a member of the World Lottery Association (WLA) and European Lotteries Association. In September 2023 it became the first iGaming supplier to receive WLA Safer Gambling Certification. EveryMatrix is proud of its commitment to safer gambling and player protection whilst producing market leading gaming solutions.

Join us on this exciting journey as we continue to redefine the iGaming landscape, one groundbreaking solution at a time.

We are looking for a passionate and dedicated Strong Junior Java Developer to join our team in Lviv!

About the job:
It is a part of EveryMatrix platform that is responsible for collecting, storing, processing and utilizing hundreds of millions of transactions from the whole platform every single day. We develop Business Intelligent solutions, reports, 3rd party integrations, data streaming and other products for both external and internal use. The team consists of 35 people and is located in Lviv. We are looking for motivated, proactive developers willing to learn modern technologies, working in a challenging and fast-paced environment. You will be working in small cross-functional Agile teams responsible for the end-to-end development and component support using the You Build It, You Run It principle.

What You'll get to do:

• Extend and optimize the Rules Engine.
• Collaborate with cross-functional teams to deliver innovative solutions.
• Participate in code reviews and contribute to team knowledge sharing.
• Troubleshoot, debug, and resolve software defects and issues.
• Assist in designing and implementing new features.
• Develop unit and integration tests to ensure software quality.
• Document code, processes, and technical specifications.
• Stay up-to-date with Java best practices and emerging technologies.
• Support deployment and maintenance of applications in development and production environments.
• Participate in Agile ceremonies and contribute to sprint planning and retrospectives.

What You need to know:

• Java Core: Deep understanding of collections, performance tuning, type systems, garbage collection, and exception handling.
• Multithreading & Concurrency: Expertise in managing asynchronous computations and ensuring thread safety.
• HTTP & RESTful Services: Strong experience in developing and consuming RESTful services.
• RDBMS & SQL: Proficiency in writing complex SQL queries and a solid understanding of RDBMS theory.
• Spring Boot: Practical experience with the Spring ecosystem, including a strong theoretical foundation.
• Apache Kafka: Proven experience with Kafka, including both practical application and theoretical knowledge.
• Unit/Integration Testing: Demonstrated ability to write testable code with adequate coverage.

Nice to Have:

• Experience with Docker & Kubernetes.
• Experience with the Google Cloud platform.
• Knowledge of Online Casino/Sports Systems.

Here's what we offer:

• Start with 22 days of annual leave, with 2 additional days added each year, up to 32 days by your fifth year with us.
• 3 sick leave days per year, no doctor's note required; 30 medical leave days with medical allowance
• Hybrid work schedule is available after the first three months of employment with 80/20 office/home format until the end of 2026. Starting from 2027, the policy will transition to primarily office-based work, with up to 10 work-from-home days per year with manager approval.
• Benefit from two Free Fridays each year, limited to one per quarter.
• Daily catered lunch or monthly lunch allowance. 
• Private Medical Subscription. 
• Access online learning platforms like Udemy for Business, LinkedIn Learning or O’Reilly, and a budget for external training.
• Gym allowance.
• Corporate English lessons.
• Support for New Parents:
• 21 weeks of paid maternity leave, with the flexibility to work from home full-time until your child turns 1 year old.
• 4 weeks of paternity leave, plus the flexibility to work from home full-time until your child is 13 weeks old.

Our office perks include on-site massages and frequent team-building activities in various locations.

At EveryMatrix, we're committed to creating a supportive and inclusive workplace where you can thrive both personally and professionally. Come join us and experience the difference!

👨‍💻We invite a Junior/Middle Java or Kotlin Developer to join our team for long-term cooperation. Gransoft develop an international health insurance portal. Our project has become especially important at this time.

▪️Office Location: Uzhhorod

Requirements:

— Strong and confident knowledge of Java or Kotlin, Hibernate, Spring, MySQL

— Experience with any software development 1-5 years

— Experience with Java/Kotlin provides a significant advantage

— An intermediate-level proficiency in English: reading, writing and speaking

— Responsible attitude to the tasks and deadlines

— Work from office only

We offer:

— Interesting and challenging project

— Creative and friendly atmosphere

— Our company policy is to welcome your ideas and suggestions

— An international team of experienced Java/Kotlin developers

— Paid vacations and days off during national holidays

— Flexible work schedule

— 8-hour workday

— Office in Uzhhorod or Gdansk

— Paid English language courses

— The company provides relocation support and, if needed, assists with the moving process and finding accommodation

More details could be given during an interview.

Please include your Telegram username in CV.

👨‍💻We invite a Junior/Middle Java or Kotlin Developer to join our team for long-term cooperation. Gransoft develop an international health insurance portal. Our project has become especially important at this time.

Office Location: Uzhhorod.
Please note: This is an on-site position only!
Hybrid and remote work arrangements are not available.

Requirements:

— Strong and confident knowledge of Java or Kotlin, Hibernate, Spring, MySQL

— Experience with any software development 1-5 years

— Experience with Java/Kotlin provides a significant advantage

— An intermediate-level proficiency in English: reading, writing and speaking

— Responsible attitude to the tasks and deadlines

— Work from office only

We offer:

— Interesting and challenging project

— Creative and friendly atmosphere

— Our company policy is to welcome your ideas and suggestions

— An international team of experienced Java/Kotlin developers

— Paid vacations and days off during national holidays

— Flexible work schedule

— 8-hour workday

— Office in Uzhhorod or Gdansk

— Paid English language courses

— The company provides relocation support and, if needed, assists with the moving process and finding accommodation

More details could be given during an interview.

Please include your Telegram username in CV.

Project description

A next-generation cross-asset data management platform to provide globally consistent data and innovative tools to support business strategy for trade/sales clients, which is built on big data architecture, highly scalable, and cloud-ready. The platform enables industry-leading analytics, client reporting, regulatory compliance, surveillance, supervisory reporting, and data science solutions (data flame). The project tech stack: Java, Scala, Spring, SQL, Kafka, Hadoop.

We are looking for a strong Senior Java Developer capable of being able to work within the team, being a mentor for team members, communicating with stakeholders, and being accountable for the outcomes of activities that are assigned.

The role of the involves working with strong development teams (2 Senior Java Developers), the opportunity to work with big data, improving knowledge in this domain, and utilizing the resources of an international bank.

Responsibilities

Design and build frameworks for ingesting/modeling the complex Risk data

Develop Low latency caching to service Front office risk systems

Setup monitoring and management for services

Provide SME support for development of automated QA scripts

Skills

Must have

Strong knowledge of Big Data technologies Hadoop Ecosystem (HDFS, Impala, HIVE, HBASE, etc.) and Apache Spark

At least 5 years of experience in software development, including professional backend software development experience;

Strong Knowledge of Java programming languages

Should be familiar with algorithms and design patterns

Familiarity with Linux environment, including scripting skills

Designing and building APIs (Java);

Java Server-side or Back-end development;

Core Java;

Java collections and multithreading;

Java Memory Management;

Database and SQL (writing stored procedures, designing table schemas).

Understanding of distributed systems.

Understanding of CI/CD workflow.

Ability to multi-task and work under pressure.

Ability to pick up new concepts and apply the knowledge.

Demonstrated problem-solving skills.

Enthusiastic and proactive approach with a willingness to learn.

The candidate is expected to be dynamic and flexible with a high energy level as this is a demanding and rapidly changing environment

Nice to have

Experience In-memory databases and caching

Job Orchestration tools like Autosys or Airflow

Apache Spark

Financial background (where possible)

Languages

English: C1 Advanced

About the Role 
We're looking for a  Backend Developer to design and build the backend of our products — REST APIs, services, and AI integrations from data model to production. You'll own features end-to-end, contribute to architectural decisions, and occasionally jump into the React frontend when it makes sense.

What You'll Do

• Design, build, and maintain backend services and REST APIs for our products – from data model through to production.
• Integrate AI / LLMs into product features.
• Design and implement clean, well-documented REST APIs (contract-first where it fits).
• Write maintainable, testable code with strong unit and integration test coverage.
• Take part in code reviews, both giving and receiving constructive feedback.
• Collaborate closely with product managers, designers, frontend engineers, and QA in an Agile team.
• Investigate and resolve bugs, and help improve performance and reliability.
• Contribute to technical and architectural decisions.
• (A plus) Occasionally contribute to the React frontend when a feature spans the stack.
   

What We're Looking For

Must-have (backend):

• 3+ years of commercial backend development experience in Java.
• Strong Java Core; hands-on experience with Spring Boot (Spring MVC, Spring Data JPA, Hibernate), Spring Security, and Spring AOP.
• Familiarity with MapStruct for entity-to-DTO mapping and Lombok.
• Practical experience designing and consuming RESTful services.
• Good SQL skills with a relational database (PostgreSQL); schema migrations with Flyway.
• Understanding of OAuth2 / JWT-based authentication and role-based access control.
• Comfortable with Docker and Docker Compose.
• Confident with Git and a standard branching workflow; familiarity with Gradle.
• Experience writing unit and integration tests (JUnit, Testcontainers).
• Genuine interest in integrating AI / LLMs into product features.
• Solid understanding of OOP, web fundamentals, and clean-code principles.
• English at Upper-Intermediate (B2) level — able to communicate in writing and on calls.
   

A big advantage:

• Frontend experience with React — JavaScript/TypeScript, HTML, CSS/SCSS, and the modern React ecosystem: client state (Zustand), server state / data fetching (TanStack Query), routing (React Router), and a modern build tool (Vite).
• Hands-on experience integrating AI / LLMs into real product features.
• Contract-first / OpenAPI workflow — OpenAPI 3 with code generation (openapi-generator).
• Experience integrating an identity provider such as Keycloak.
• AWS exposure (EC2, RDS, CloudWatch) and structured (JSON) logging.
• End-to-end testing with Playwright.

Our client is one of the leading companies on the market which provides Big Data, Data Integration, Data Preparation and Enterprise Application Integration software and services. Its products allow to build data integration process, migrate data safely, process big amount of data, cleanse data and check its quality.

Connector (aka Component) is a core element of the products, which allows to connect, extract data from a data source, transform data according to business needs and load data back to some storage. It is used in traditional software such as Studio for Data Integration as well as in the modern Cloud services.

Continuous emerging of new technologies and data repositories lead to demand growth of creating new connectors and adapting the existing ones.

For this reason, we are looking for a Junior Java developer to join the team to address the demand and provide our client with the best quality service.
 

Requirements:

• Good knowledge of Java Core 8
• Some experience with SQL (knowledge of JDBC is a huge plus)
• Understanding and some experience in testing techniques (JUnit)
• English (both spoken and written) at least at Intermediate level that allows communicating with an international team on a daily basis

 Optional but desirable:

• Pet projects on Java Core
• Knowledge of JSON, XML
• Knowledge or experience with development and CI tools: Git/GitHub, Maven, Docker

Job responsibilities:

• Design and implement Talend Connectors
• Unit and Integration testing
• Respond to feature requests, bug reports, performance issues and ad-hoc questions

Advantages:

• Smooth onboarding process
• Working under the supervision of a skilled teammate
• Chance to work with a great variety of technologies and DBs (both SQL and non-SQL such as Snowflake, PostgreSQL, Mongo, Cassandra, DynamoDB, Neo4j)
• Work collaboratively in a distributed international team (France, Germany, China)

Please provide your CV and LinkedIn profile. We demand your LinkedIn profile with actual working experience to move forward with your application!

Fundomate is looking for a Senior Java Back-End Developer to join our team. Fundomate is an innovative fintech company operating in the alternative lending space and providing both direct-to-business and white-label turnkey solutions.

You will be good match if:

- You have history of solving non trivial problems in one of your previous projects

- You have wide technology background (backend, frontend, devops, ops, mobile development, etc), so you will understand the connections between technologies and expand this knowledge with domain and business needs. 

- You have experience working in US fintech domain 

We will be good match if:

- You want to solve (or learn to solve) complex business problems

- You want to experiment with processes/development technics/tools

- You are interested in continuous improvement and automation of product and working process

Requirements:

- 6+ years of experience developing web applications

- 3+ years of experience in any IoC & DI framework (Spring, Quarkus, Micronaut, etc.)

- TDD experience in production is a must have

- Experienced in pair programming

- Good knowledge of MicroServices (Kubernetes knowledge is a plus)

- Experience working with tools like Git, Gradle, Jenkins or similar CI/CD

- Working experience in Industry Standard protocols related API Security including OAuth (KeyCloak is a plus)

- Working experience with RDBMs like Postgres/MySQL or any similar

- Understanding of asynchronous message-based communication like Kafka, GCP Pub/Sub, AWS SNS/SQS, etc. (Kafka as an advantage)

- Strong Agile/Scrum/Kanban development experience

- Experience in third party systems integration (XML or JSON api)

- Knowledge of any cloud provider (AWS as an advantage)

Our technical Stack:

- Java 25

- Microservices (Quarkus)

- Postgresql/MySQL

- Kafka

- Keycloak

- Kubernetes & Docker

- AWS (EKS, MSK, RDS, etc.)

- Gradle

- Bitbucket pipelines, gitops approach

- Lombok, MapStruct, Flyway

We offer:

- Innovative product with modern technology stack

- Competitive salary (paid in $)

- Social package (paid vacations, sick leaves and etc)

- PE accounting and support

- WFH and remote working mode possibility, Ukrainian working hours

- No bureaucracy, micromanagement and time-tracking

Project Description:

A next-generation cross-asset data management platform to provide globally consistent data and innovative tools to support business strategy for trade/sales clients, which is built on big data architecture, highly scalable, and cloud-ready. The platform enables industry-leading analytics, client reporting, regulatory compliance, surveillance, supervisory reporting, and data science solutions (data flame). The project tech stack: Java, Scala, Spring, SQL, Kafka, Hadoop.

We are looking for a strong Senior Java Developer capable of being able to work within the team, being a mentor for team members, communicating with stakeholders, and being accountable for the outcomes of activities that are assigned.

The role of the involves working with strong development teams (2 Senior Java Developers), the opportunity to work with big data, improving knowledge in this domain, and utilizing the resources of an international bank.

Responsibilities:

• Design and build frameworks for ingesting/modeling the complex Risk data
• Develop Low latency caching to service Front office risk systems
• Setup monitoring and management for services
• Provide SME support for development of automated QA scripts

Mandatory Skills Description:

• Strong knowledge of Big Data technologies: Hadoop Ecosystem (HDFS, Impala, HIVE, HBASE, etc.) and Apache Spark. Green flags: Spark, Hive, Hadoop.
• At least 5 years of experience in software development, including professional backend software development experience;
• Strong Knowledge of Java programming languages
• Should be familiar with algorithms and design patterns
• Familiarity with Linux environment, including scripting skills
• Designing and building APIs (Java);
• Java Server-side or Back-end development;
• Core Java;
• Java collections and multithreading;
• Java Memory Management;
• Database and SQL (writing stored procedures, designing table schemas).
• Understanding of distributed systems.
• Understanding of CI/CD workflow.

• Ability to multi-task and work under pressure.
• Ability to pick up new concepts and apply the knowledge.
• Demonstrated problem-solving skills.
• Enthusiastic and proactive approach with a willingness to learn.
• The candidate is expected to be dynamic and flexible with a high energy level as this is a demanding and rapidly changing environment

Nice-to-Have Skills Description:

• Experience In-memory databases and caching
• Job Orchestration tools like Autosys or Airflow
• Apache Spark
• Financial background (where possible)

On behalf of our Client from the US, Mobilunity is looking for a Senior Backend Architect (Java).
 

You will work on mission-critical backend systems powering a large-scale US e-commerce platform. The role involves designing and developing backend services, integrations, inventory synchronization, order processing, pricing logic, and marketplace integrations supporting a high-traffic online business.

This is not a typical feature-delivery role. You’ll participate in architectural discussions, solve complex engineering problems, and collaborate directly with technical and business stakeholders to deliver scalable solutions.
 

Candidates must be available to work primarily during US business hours, with a preferred schedule of 1:00 PM – 8:00 PM CET.

What we’re looking for:

We are not looking for someone who simply implements requirements.
 

We are looking for an engineer with a strong consultant mindset who:

• understands business goals before proposing technical solutions;
• is comfortable working with ambiguous requirements;
• asks the right questions instead of waiting for detailed specifications;
• evaluates architectural trade-offs between scalability, performance, operational complexity, and cost;
• independently designs scalable solutions;
• communicates technical decisions clearly to both engineering and business stakeholders;
• takes ownership of technical decisions and their business impact;
• leverages AI tools to improve engineering productivity while applying independent technical judgment.
   

Requirements:

• 8+ years of professional Java development experience.
• Strong expertise in Java SE and Spring Framework (Core, MVC, Spring Boot).
• Solid experience designing scalable backend systems and distributed architectures.
• Strong understanding of software architecture principles and design patterns.
• Experience with microservices and event-driven architecture.
• Experience with Kafka or similar messaging technologies.
• Strong SQL skills and experience with relational databases.
• Experience working with AWS or other cloud platforms.
• Strong analytical and problem-solving skills.
• Ability to evaluate scalability, performance, reliability and cost trade-offs.
• Experience participating in architectural discussions and technical decision-making.
• Experience communicating directly with business stakeholders.
• Excellent written and spoken English.
   

Responsibilities:

• Design scalable backend architecture for business-critical systems.
• Translate business requirements into technical solutions.
• Evaluate architectural alternatives and justify technical decisions.
• Improve platform scalability, performance and operational efficiency.
• Design integrations with internal systems and third-party services.
• Participate in technical strategy and long-term architecture planning.
• Collaborate directly with the CTO, Tech Lead and business stakeholders.
• Mentor engineers and contribute to engineering best practices.
• Promote AI-assisted engineering workflows across the development process.
• Take ownership of complex technical domains from design through delivery.
   

Nice to have:

• SAP Commerce (Hybris).
• Marketplace or e-commerce experience.
• High-load distributed systems.
• Automotive, retail or e-commerce background.
• Startup experience.
• Experience working directly with CTOs, founders or product leadership.
• Previous experience as a Tech Lead or Software Architect.
• Experience with AI-assisted software development (Cursor, Claude Code, ChatGPT, etc.).
   

In return we offer:

• The friendliest community of like-minded IT-people
• Open knowledge-sharing environment – exclusive access to a rich pool of colleagues willing to share their endless insights into the broadest variety of modern technologies
• Mobilunity Medical Insurance program designed to attend our teams’ needs
• Paid vacations and sick leaves, including 5 paid days per year that don’t require a sick note
• Perfect office location in the city-center (900m from Lukyanivska metro station with a green and spacious neighborhood) or remote mode engagement: you can choose a convenient one for you, with a possibility to fit together both
• No open-spaces setup – separate rooms for every team’s comfort and multiple lounge and gaming zones
• English classes in 1-to-1 & group modes with elements of gamification
• Neverending fun: sports events, tournaments, music band, multiple affinity groups
   

Come on board, and let’s grow together!

• Project Description:

  Our Client is a leading global financial markets infrastructure and data provider. Their purpose is driving financial stability, empowering economies and enabling customers to create sustainable growth.
  
  With capabilities in data, indices and analytics, capital formation, trade execution, clearing and risk management, they operate at the heart of the world's financial ecosystem and enable the sustainable growth and stability of their customers and their communities.
  
  We are seeking a highly motivated Software Engineer with hands-on experience in development and Cloud platform to join our team where your experience will make a significant impact on the world's leading financial markets infrastructure!

• Responsibilities:

  • Be responsible for the whole software process, including design, planning, coding, automated unit testing and CI/CD and deployment process.
  • Break down sophisticated problems into its essentials, design and implement features.
  • Build well-structured and maintainable code.
  • Participate in code review to ensure code quality and standard methodologies.
  • Act as an agile developer, flexible to play multiple roles in the team.
  • Be flexible to learn new technologies as required by the project and find opportunities for improvements.
  • Lead in identifying and solving software defects and issues.
  • Actively participate in project planning sessions with team members to analyze requirements and estimates of work.
  • Supply the documentation of software solutions.

• Mandatory Skills Description:

  • 8+ years of proven experience as a Senior Software Engineer with extensive experience in software development..
  • Expertise in Java (v11, v18). Strong understanding of object-oriented principles
  • Experience in OpenJDK (v18), Debian.
  • Experience in building Cloud Native application, preferably Amazon AWS or Microsoft Azure
  • Experience working with Relational databases and caching technologies like Redis
  • Expertise in version control software such as GIT etc.
  • Familiar with CI/CD like GitHub, GitLab, DevSecOps etc.
  • Experience in writing Shell/Bash/Python scripts
  • Strong technical foundation with expertise in backend technologies
  • Basic knowledge of frontend development technologies (JavaScript, HTML, CSS etc.)

• Nice-to-Have Skills Description:

  • BS/MS in Computer Science/Computer Engineering

• Languages:
  • English: C1 Advanced

We are looking for an experienced Senior Java Full Stack Engineer (Java+Python, React) to join our development team.

Our customer – integrated Shipping Services has set itself apart as an independent carrier with a fresh, unique approach. His strategy as a global niche carrier offers distinctive advantages to customers worldwide. We have created a smart, efficient network that ensures stable, reliable services, and we have made it our mission to focus on the needs of our customers, which stand at the heart of all our decisions. The main idea of our product operates in select trades, where it has a competitive advantage and where it can provide superior service. We maintain a flexible partnership approach with other major carriers, and our new line structure is a much-needed alternative to customers concerned about the current alliance-dominated market.

Responsibilities:

• Hands-on full-stack development of innovative applications
• Owning the entire development cycle, including design, architecture, development, and DevOps
• Working in XP with Remote pairing
• designing, developing, and deploying cloud/hybrid-based solutions

Requirements:

• BS degree in Computer Science or equivalent combination of education and experiencet
• 5-6+ years of experience with Java
• 1 year of experience with Python
• 1 year of experience in front-end development with React
• Experience with Functional Programming and Java Streams
• Experience with AI (Cloud is preferable)
• Experience in development in Kotlin – nice to have
• Familiarity with the following design concepts: micro-services, service discovery, circuit breaker
• Self-starter with the ability to appropriately prioritize and plan complex work in a rapidly changing environment
• Versatility and the capability to switch easily between different tasks and technologies
• Experience in assessing a broad range of information solutions and products
• Strong critical thinker with problem-solving aptitude
• Upper-intermediate English level - verbal and written

We offer*:

• Flexible working format - remote, office-based or flexible
• A competitive salary and good compensation package
• Personalized career growth
• Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more)
• Active tech communities with regular knowledge sharing
• Education reimbursement
• Memorable anniversary presents
• Corporate events and team buildings
• Other location-specific benefits

*not applicable for freelancers

Are you ready to take ownership of mission-critical backend systems in a high-load, transaction-heavy environment? 

We are looking for a Senior Java Developer to join our Payments Domain team in Warsaw.

This is a hybrid role with 3 days per week in the office, giving you the perfect balance between collaboration and flexibility. 

At Sigma Software, we value engineering excellence, multicultural teamwork, and delivering secure, high-performance solutions.

Why join us? You’ll work on a platform processing millions of transactions daily, contribute to architectural decisions, and be part of a company where innovation and ownership are encouraged.
 

Customer

Our customer is a well-established international company in the iGaming industry, known for its engineering-driven culture and multicultural team distributed across multiple countries. Operating multiple brands across various markets, the company delivers secure, high-performance digital platforms recognized for reliability and scalability.
 

Project

You will be part of the Payments Domain team, responsible for developing and maintaining a large-scale payments platform built on modern microservices architecture. The platform processes millions of secure transactions daily, supporting multiple brands and geographies. The work focuses on scalability, reliability, and performance in a high-load environment, covering everything from integration with payment providers to transaction monitoring and compliance.

Requirements:

• 5+ years of commercial experience with Java and Spring Boot
• Strong experience with MySQL and Kafka
• Proven track record working with microservices architecture in high-traffic, high-load systems
• Experience developing high-performance backend solutions for transaction-heavy platforms
• Ownership mindset with the ability to deliver services end-to-end
• Excellent communication skills in English (C1 level), both written and verbal
• Experience with Kotlin
   

Responsibilities:

• Design, develop, and maintain backend services for the payments platform using Java and Spring Boot
• Ensure high availability, scalability, and performance of transaction processing systems
• Collaborate with cross-functional teams to define technical requirements and deliver solutions end-to-end
• Implement integrations with payment service providers and internal systems
• Participate in architectural discussions and contribute to system evolution in a microservices environment
• Monitor, troubleshoot, and optimize services in production
• Ensure compliance with security, regulatory, and operational standards
• Drive continuous improvement in code quality, testing, and deployment practices

Чи готові ви взяти на себе відповідальність за критично важливі backend-системи у високонавантаженому середовищі з великою кількістю транзакцій?

Ми шукаємо Senior Java Developer до команди Payments Domain у Варшаві.

Це hybrid-роль із відвідуванням офісу 3 дні на тиждень, що забезпечує баланс між командною співпрацею та гнучкістю.

У Sigma Software ми цінуємо інженерну досконалість, мультикультурну командну роботу та створення безпечних високопродуктивних рішень.

Чому варто приєднатися? Ви працюватимете над платформою, яка щодня обробляє мільйони транзакцій, братимете участь у прийнятті архітектурних рішень та станете частиною компанії, де заохочуються інновації та відповідальність за результат.

Клієнт

Наш клієнт — міжнародна компанія у сфері iGaming із сильною engineering-культурою та мультикультурною командою, розподіленою між кількома країнами. Компанія керує кількома брендами на різних ринках і створює безпечні високопродуктивні цифрові платформи, відомі своєю надійністю та масштабованістю.

Проєкт

Ви станете частиною команди Payments Domain, відповідальної за розробку та підтримку масштабної платіжної платформи, побудованої на сучасній мікросервісній архітектурі. Платформа щодня обробляє мільйони безпечних транзакцій, підтримуючи різні бренди та географії. Робота зосереджена на масштабованості, надійності та продуктивності у високонавантаженому середовищі — від інтеграції з платіжними провайдерами до моніторингу транзакцій і забезпечення відповідності вимогам.

Вимоги:

• 5+ років комерційного досвіду з Java та Spring Boot 

• Впевнений досвід роботи з MySQL та Kafka 

• Підтверджений досвід роботи з мікросервісною архітектурою у високонавантажених системах 

• Досвід розробки високопродуктивних backend-рішень для платформ із великою кількістю транзакцій 

• Ownership mindset та здатність вести сервіси end-to-end 

• Відмінні комунікаційні навички англійською мовою (рівень C1), усно та письмово 

• Досвід роботи з Kotlin

Обов’язки:

• Проєктування, розробка та підтримка backend-сервісів платіжної платформи з використанням Java та Spring Boot 

• Забезпечення високої доступності, масштабованості та продуктивності систем обробки транзакцій 

• Співпраця з кросфункціональними командами для визначення технічних вимог і реалізації рішень end-to-end 

• Реалізація інтеграцій із платіжними провайдерами та внутрішніми системами 

• Участь в архітектурних обговореннях і розвиток системи в мікросервісному середовищі 

• Моніторинг, troubleshooting та оптимізація сервісів у production 

• Забезпечення відповідності вимогам безпеки, регуляторним та операційним стандартам 

• Постійне вдосконалення якості коду, тестування та процесів деплою