Java Engineer

Data & Backend Systems — SimX Platform

Full-Time | Remote | Contractor

About Telkoa

Telkoa builds SimX, a SIM and eSIM management platform for telecom operators. We process millions of SIM lifecycle events, network signaling messages, and usage records daily across multiple cloud environments (Hetzner K3s, AWS EKS, VMware on-prem), serving telecom operators in Europe, Latin America, and Southeast Asia.

SimX is a data-intensive platform at its core. Real-time Kafka event streaming, CDC pipelines, time-series aggregation, and geospatial analytics are central to everything we do. We are a small, senior team that ships fast. No layers of management, no ticket factories.

The Role

We are looking for a Java Engineer to join the Platform R&D team and work on the data-intensive systems that power SimX. You will work alongside a senior engineer on Kafka event pipelines, PostgreSQL data operations, aggregation jobs, and the Java Spring Boot microservices that serve telecom operators across three continents.

This is a hands-on engineering role focused on data at scale. You will work with CDC pipelines, write and optimise raw SQL against TimescaleDB hypertables, contribute to batch aggregation jobs, and build API features. What you build will handle millions of events daily in production.

What You Will Work On

Data Pipelines & Event Processing (~35%)

- Work with Kafka to process real-time SIM lifecycle events, IMSI swaps, and connectivity state changes across operator networks.

- Learn and contribute to the CDC pipeline (Debezium) that replicates PostgreSQL changes to Kafka topics for downstream enrichment.

- Contribute to Kafka Connect configurations — sink and source connectors that move data between Kafka and PostgreSQL.

- Implement data validation, transformation, and enrichment logic within pipelines.

- Work with Avro schemas and the Confluent Schema Registry to maintain data contracts across services.

Database & Analytics (~30%)

- Write and optimise raw SQL queries against PostgreSQL at scale. SimX does not use JPA/Hibernate — all database access is direct SQL via custom repository classes.

- Work with TimescaleDB hypertables for time-series event data — understand chunking, retention policies, and query patterns for time-series workloads.

- Contribute to aggregation pipelines (pg_cron scheduled jobs) that roll up raw telemetry into hourly and daily analytics for operator dashboards.

- Maintain database schemas and write migration scripts — SimX uses dated, idempotent SQL migrations.

- Gain exposure to PostGIS geospatial queries and Uber H3 hexagonal indexing used in location analytics.

Backend API Development (~25%)

- Build and maintain features across SimX's Java Spring Boot microservices — SIM lifecycle workflows, provisioning APIs, campaign management, and usage tracking.

- Implement and optimise REST API endpoints consumed by telecom operator dashboards and external integrations.

- Write unit and integration tests. Participate in code reviews — both giving and receiving feedback.

- Document your work — API specs, runbooks, and technical notes in the internal knowledge base (Outline).

Growth (~10%)

- Learn the telecom domain through hands-on work — SIM lifecycle, IMSI provisioning, eSIM profiles, OTA updates, network measurement reports.

- Develop deeper expertise in event-driven architecture, Confluent Kafka ecosystem, and data engineering patterns.

- Pair with the senior engineer on complex data pipeline and architecture problems.

Requirements

Must Have

- 2–3 years of production experience with Java and Spring Boot. You have built and maintained real services in production.

- Strong SQL skills — PostgreSQL preferred. Comfortable writing complex queries, designing schemas, optimising performance, and understanding query execution plans. Experience with raw SQL (not just ORM-generated queries) is important.

- Basic understanding of message brokers and event-driven patterns (Kafka, RabbitMQ, or similar). You do not need deep expertise, but you should understand how events flow through a system.

- Experience with or strong interest in data processing at scale — batch jobs, aggregation pipelines, large dataset operations.

- Familiarity with REST API design and implementation.

- Experience with Git-based workflows and code review processes.

- Comfortable working in a remote, async-first environment with communication primarily in English.

Strong Plus

- Hands-on experience with Apache Kafka in production.

- Experience with TimescaleDB, time-series databases, or PostgreSQL extensions.

- Experience with CDC tools (Debezium, Kafka Connect).

- Familiarity with Avro, Protobuf, or other schema-based serialisation.

- Experience with Docker and basic Kubernetes concepts.

- Proficiency with AI-assisted development tools (Claude Code, Cursor, GitHub Copilot) — we value engineers who use AI to multiply their output.

- Any telecom or SIM/eSIM domain knowledge.

- Familiarity with GitLab CI/CD pipelines.

How We Work

- Tools: Linear (project management), GitLab (code + CI/CD), Outline (knowledge base), Slack (communication).

- Process: Issues tracked in Linear. Agile but lightweight — no ceremonies for the sake of ceremonies.

- Cadence: Async-first. Weekly sync with the CEO/CTO.

- Compensation: Competitive monthly rate, contractor agreement, monthly invoicing.

Why This Role

Most mid-level roles at larger companies mean building CRUD endpoints in a small corner of a system. At Telkoa you will work across the full data stack — from Kafka CDC pipelines to TimescaleDB aggregation to raw SQL optimisation to REST APIs — and see your code handling millions of real events in production for telecom operators within days.

You will work alongside a senior engineer who can help you grow into a data engineering specialist, in a domain (telecom SIM/eSIM) that is technically demanding and commercially growing. The team is small enough that your contributions are visible and large enough that you are not carrying the platform alone.

To apply: careers@telkoa.com

Application Question(s):

• How many years of production experience do you have with Java and Spring Boot?
• Describe your SQL experience, ideally with PostgreSQL. How comfortable are you writing complex raw SQL (not just ORM-generated queries), designing schemas, optimising performance, and reading query execution plans?
• What is your experience with message brokers and event-driven systems (Kafka, RabbitMQ, or similar)? Describe how events flow through a system you've worked on, and any hands-on Kafka experience you have.
• Describe your experience with or interest in data processing at scale — batch jobs, aggregation pipelines, or large dataset operations. If you've built something handling high volumes, what was it and what challenges did you face?
• What tools do you use to multiply your engineering output? Do you use AI-assisted development tools like Claude Code, Cursor, or GitHub Copilot? If yes, describe how you use them in your workflow.
• Do you have any telecom or SIM/eSIM domain knowledge (e.g. SIM lifecycle, IMSI, eSIM profiles, OTA updates, network signaling)? This is a plus, not a requirement.
• What is your expected monthly compensation in EGP?
• What is your notice period at your current role?
• Are you comfortable working fully remote and async-first, communicating primarily in English with a globally distributed team?

Work Location: Remote