Middle/Senior Backend Engineer

* BFF Layer — Backend-for-Frontend services orchestrating complex Web3 operations

Tech Stack:

* Language: Go (go-ethereum, ethkit, idiomatic concurrency patterns)

* Databases: MongoDB, PostgreSQL, Redis

* Message Queue: NATS, RabbitMQ, Kafka

* API: REST, WebSocket, gRPC, OpenAPI (Swagger)

* Blockchain Infrastructure:

* ZK Stack / ZKsync Era: EraVM, zksolc/zkvyper compilers, system contracts, bootloader, native Account Abstraction on zkSync-family chains

* Account Abstraction (ERC-4337): EntryPoint (v0.6–v0.8), UserOperation lifecycle (prepare→sign→submit→confirm), bundler and paymaster roles, ERC-7562 validation rules, ERC-6492 signature validation for undeployed accounts

* Ethereum L1: go-ethereum, abigen for smart contract bindings, RPC and indexer semantics

* Smart Contracts: Solidity, ERC-20/721/1155, modular account standards (ERC-7579 / ERC-6900), session keys (ERC-7710 / ERC-7715)

* Signature Schemes: EIP-712 typed data, ERC-1271 contract signatures, WebAuthn/passkey (P-256)

* Infrastructure: Docker, Kubernetes, GitLab CI/CD, Graylog

Key Technical Challenges:

* ZK Stack Integration: Working with EraVM execution environment, native Account Abstraction on zkSync-family chains, double resource accounting (EE gas + native computational resources), L1↔L2 communication via ZKsync Gateway, finality and reorg behavior

* Account Abstraction Backend Services: Implementing the ERC-4337 UserOperation lifecycle, integrating with bundlers and paymasters, handling gas estimation failure modes and counterfactual deployment

* Smart Contract Interaction: Generating Go bindings via abigen, handling factory dependencies for contract deployment, implementing EIP-712 transaction signing and ERC-1271 signature verification

* Session Keys & Delegated Permissions: Supporting scoped, time-limited, contract-allowlisted authority (ERC-7710 / ERC-7715) for gasless, prompt-free gameplay transactions

* Event Processing: Building blockchain event scanners for multiple chains (Ethereum, Polygon, Xsolla ZK), implementing reorg handling and transaction finality tracking

* High-Availability Architecture: Designing resilient microservices for NFT marketplace and wallet backends with real-time WebSocket updates

Responsibilities
* Develop backend services using Go with ethkit and go-ethereum for Ethereum interactions and RPC integration

* Integrate with ZK Stack infrastructure: work with EraVM, system contracts, and L1↔L2 messaging

* Build and maintain wallet backend indexing integrations for real-time token balance tracking and webhooks (via internal indexer or third-party providers)

* Design and implement APIs for NFT marketplace and orderbook services, including on-chain order matching and settlement flows

* Implement smart contract interaction layer using abigen-generated Go bindings for ERC-20/721/1155 tokens

* Build Account Abstraction (ERC-4337) backend support: UserOperation submission and monitoring, paymaster gas-sponsorship logic, session-key issuance and revocation

* Develop blockchain event scanners with reorg handling for Ethereum, Polygon, and Xsolla ZK chains

* Implement BFF (Backend-for-Frontend) services orchestrating complex multi-chain operations

* Design efficient caching and indexing strategies for on-chain data using Redis and MongoDB

* Write comprehensive tests including integration tests with local ZKsync test environment

* Document APIs using OpenAPI/Swagger specification

* Monitor and troubleshoot production systems, handle blockchain-specific edge cases (stuck transactions, gas estimation)

Nice to Have
Required:

* 2+ years of commercial experience with Go

* Strong understanding of MongoDB and PostgreSQL (query optimization, indexing)

* Experience with Redis for caching and session management

* Knowledge of message queues (NATS, RabbitMQ, or similar)

* Experience designing and implementing REST APIs with OpenAPI/Swagger

* Understanding of microservices architecture patterns

* Experience with Docker and container orchestration basics

* Proficiency with Git and GitLab CI/CD

* Solid understanding of distributed systems concepts

Preferred:

* Experience with Ethereum/EVM blockchain integration:

* Working with go-ethereum library and RPC nodes

* Smart contract interaction via ABI bindings (abigen)

* Understanding of transaction lifecycle, gas estimation, nonce management

* Knowledge of ZK Stack / ZKsync Era:

* EraVM execution model and differences from EVM, including native Account Abstraction on zkSync-family chains

* System contracts (ContractDeployer, NonceHolder, etc.)

* L1↔L2 communication, bridging, and finality/reorg behavior

* Working knowledge of ERC-4337 Account Abstraction:

* EntryPoint contract and the UserOperation lifecycle

* Bundler and paymaster roles, gas estimation failure modes

* Session keys and delegated permissions (ERC-7710 / ERC-7715)

* Familiarity with signature schemes: EIP-712 typed data, ERC-1271 contract signatures, WebAuthn/passkey signers

* Exposure to AA infrastructure providers (any of: Sequence, thirdweb, Privy, Dynamic, Turnkey, Pimlico, Alchemy, Biconomy, ZeroDev, Safe{Core}) for wallet, indexer, or transaction-relay integrations

* Knowledge of token standards (ERC-20, ERC-721, ERC-1155) and their implementation details

* Experience with blockchain event processing: event scanning, reorg handling, finality

* Understanding of DeFi concepts and NFT marketplace mechanics

* Experience with Kubernetes for container orchestration