Java Software Engineer

Overview

The Java Software Engineer at APX (Now Aster) will architect and optimize backend systems for blockchain data processing, build high-performance APIs, implement off-chain logic for DeFi applications, and develop microservices to improve wallet interactions and transaction queuing.

Main Responsibilities

• Architect and optimize backend systems for blockchain data (indexing, RPC interactions, event streaming).
• Build high-performance APIs for frontends and smart contracts using REST, WebSocket, and GraphQL.
• Implement off-chain logic for DeFi apps including price oracles and risk engines.
• Develop microservices for wallet interactions, transaction queuing, and gas optimization.
• Ensure reliability of critical infrastructure through node management, load balancing, and failover systems.
• Collaborate with smart contract developers on protocol integrations.

Required Skills and Experience

• 3+ years of backend development using Java (also Rust, TypeScript, Go).
• Experience with blockchain technologies (JSON-RPC, ethers.js/web3.py, transaction lifecycle).
• Expertise in database optimization (PostgreSQL, TimescaleDB, Redis).
• Familiarity with asynchronous architectures (Kafka, RabbitMQ, Celery).
• Solid knowledge of the Web3 stack, including EVM and indexers.
• Understanding of security practices such as rate limiting, sanitization, and replay protection.
• Cloud deployment experience with AWS/GCP, containerization, and Infrastructure as Code (IaC).

Key skills/competency

Java, blockchain, backend, microservices, APIs, cloud, security, async, database, integration