Senior Backend Engineer – Large-Scale Transaction Systems - 26/01/2026 08:16 EST -- 2

Engagement type: Freelance / Contract
Duration: Initial 3–6 months (extension possible)
Location: Remote
Start: ASAP

Project overview

We are looking for a senior, hands-on systems engineer to help design and build high-scale automation and simulation systems for transaction-heavy digital procurement workflows (simulated buying).

The core challenge is building distributed, resilient systems that can orchestrate large numbers of concurrent, human-like actors interacting with well-known web-based platforms in a realistic and reliable way.

This role is engineering-heavy and suited for someone who enjoys solving hard problems around scale, concurrency, reliability, and system behavior modeling.

What you’ll be working on

Designing and implementing distributed automation / simulation architectures

Orchestrating thousands of concurrent browser or API-based workflows

Building systems that model realistic user behavior patterns (timing, sequencing, variability)

Managing session state, retries, failures, and partial success scenarios

Implementing observability: logging, metrics, error tracking

Collaborating on architecture decisions and trade-offs (latency vs reliability, cost vs scale)

Required experience

5+ years of senior backend / systems engineering experience

Strong hands-on experience with Python (async), Go, or Node.js

Experience building high-concurrency, distributed systems

Solid understanding of:

Async processing

Queues / workers (e.g. SQS, Kafka, Redis)

State management at scale

Experience with browser automation frameworks (e.g. Playwright, Puppeteer) or complex API-driven workflows

Strong debugging and problem-solving skills under real-world constraints

Background in one or more of:

Trading systems

Marketplaces

AdTech / Fraud systems

Load testing or simulation platforms

Gaming or anti-cheat systems

Familiarity with behavioral modeling or synthetic user generation

Strong opinions on system design — and the ability to defend them

What this is not

Not a simple scraping task

Not a junior automation role

Not a basic CRUD application

This is a senior engineering role requiring architectural thinking and production-grade implementation.

Engagement details


How to apply

Please include:

A short description of similar systems you’ve built (focus on scale & complexity)

We need a full CV, without a CV your application will be rejected

Your preferred tech stack

Any relevant GitHub or project references (if shareable)

Contracting: You will be contracting with the client directly, and we will take a one-time introduction fee, but will not be responsible for any tasks or development efforts