Technical Lead & Software Engineer — Architecture · Technical ownership

I take ownership of technical problems, from architecture to production.

I design and build reliable software systems, lead technical decisions, and turn complex product problems into working products.

Illia Losiev

fig. 01 — Illia Losiev

Open to Senior, Lead and Staff roles, and to selected consulting work.

Who

An experienced software engineer with a long background in backend systems.

What

Backend systems, architecture, and technical leadership for product teams.

How

Owns problems end-to-end: understanding, decision, implementation, operation.

Why it matters

Turns ambiguous requirements into reliable software running in production.

01 — How I work

From problem to outcome

Every engagement follows the same arc. The work is not the code in the middle — it is carrying a difficult problem all the way to a measurable result.

  1. 01 Problem A hard technical problem exists.
  2. 02 Understanding Product and technical constraints, first.
  3. 03 Decision Options weighed, trade-offs made explicit.
  4. 04 Ownership Drives implementation through the hard parts.
  5. 05 Production Shipped, observed, operated for real.
  6. 06 Outcome A measurable change for product and team.

02 — Selected work

Systems I have built and owned

The problem and the outcome of each system; the full record — context, role, decisions, engineering — is on the work page.

AI Agent Platform

EasyLlama · 2025 – present

Architected and own the production AI agent platform inside a multi-tenant Rails SaaS product — the assistants, routing, tooling, conversation state and evaluation infrastructure that turn LLM calls into dependable product workflows.

problem
Isolated AI interactions do not compose. Each new capability meant re-solving routing, permissions, conversation state and quality, and LLM behaviour was hard to trust in a product where tenants must never see each other's data.
outcome
Customers build dashboards, query their data and produce, save and export reports through the assistants instead of waiting on engineering. New capabilities are added as tools on shared infrastructure, and regressions in agent behaviour are caught by the evaluation suites before release rather than by customers.

Ruby · Rails · PostgreSQL · Redis · Sidekiq · LLM APIs

Airbnb and PMS booking synchronisation

boomnow · 2024 – 2025

Owned the architecture and implementation of the Airbnb integration for a hospitality platform: keeping bookings consistent between the product and external property-management systems.

problem
Two systems each believe they own the booking. Synchronisation has to survive partial failures, late updates and multi-unit allocation, in a multi-tenant environment where a bug is visible to a guest standing at a door.
outcome
Bookings from Airbnb and third-party PMS platforms flow into the platform and are allocated across units through one set of workflows, and integration problems can be diagnosed from tenant state without an engineer reproducing them.

Ruby · Rails · PostgreSQL · Sidekiq · Airbnb API

SaaS payment platform

MobiDev · 2022 – 2023

Led the development of a SaaS payment platform from the ground up as Tech Lead — technical planning, engineering workflows and release coordination.

problem
Standing up a payments system from zero while keeping releases predictable for a team that was forming at the same time.
outcome
A platform delivered from an empty repository with a repeatable release process, and deployments about a quarter faster than the starting point.

Ruby · Rails · PostgreSQL · CI/CD

High-load crawling and exchange-data platform

DigitalBridges · 2016 – 2022

Core architecture, large-scale web crawlers and crypto-exchange integrations for a data-heavy platform, over five years of growth and production hardening.

problem
Crawling at volume without being blocked, keeping exchange data consistent, and making search over a large dataset fast enough — while a legacy frontend and long-standing production issues slowed the team down.
outcome
A platform that stayed stable and consistent as the dataset and load grew over five years, with the long-standing production issues resolved and a frontend the team could keep evolving.

Ruby · Rails · PostgreSQL · Redis · Vue.js · Web scraping

03 — Technical case study

From isolated AI features to a multi-agent platform

How a multi-tenant Rails SaaS product moved from one-off AI interactions to a platform of bounded assistants with routing, shared tools and evaluation infrastructure — and what was traded to get there.

Problem

AI features had started as isolated interactions. Every new capability meant re-solving routing, permissions, conversation state and quality — in a multi-tenant product where tenants must never see each other's data.

Decision

Bounded assistants on a shared platform: a routing layer, reusable tool abstractions where permissions are enforced, shared conversation state, and evaluation infrastructure so reliability is measured, not hoped for.

Read the full case study

04 — Technical leadership

How I lead technical work

Leadership shows up in engineering behaviour, not in titles.

Architecture

Design systems that can evolve without unnecessary complexity.

Technical decisions

Choose technologies and approaches based on constraints, not hype.

Ownership

Take responsibility for outcomes rather than just assigned tickets.

Delivery

Break complex technical problems into incremental, deliverable pieces.

Reliability

Think about failure modes, observability and operational behaviour.

Technical debt

Know when debt is acceptable and when it becomes a business risk.

Team enablement

Create systems, documentation and decisions that let other engineers move faster.

Product alignment

Technical decisions should serve product and business goals.

05 — Principles

How I think about engineering

  1. 01Understand the problem before designing the solution.
  2. 02Prefer simple architecture until complexity is justified.
  3. 03Make trade-offs explicit.
  4. 04Optimise for maintainability, not cleverness.
  5. 05Treat production behaviour as part of engineering.
  6. 06Build systems other engineers can understand.
  7. 07Technical decisions should serve product goals.
  8. 08Own outcomes, not just implementation.

06 — Work with me

Have a difficult technical problem?

I work with teams and founders who need senior technical ownership — from architecture and backend systems to technical rescue and product delivery.

01

Technical audit

Review an existing system and identify architectural, reliability and scalability problems — with a prioritised plan, not a report.

02

Architecture

Design the technical foundation for a new product or a major feature, including the decisions you will be living with for years.

03

Backend engineering

Build APIs, integrations, data processing and the core business systems the product depends on.

04

Technical rescue

Stabilise or restructure a system that has become slow, fragile or difficult to change.

05

MVP engineering

Turn a product idea into a production-ready technical foundation that will not need rewriting after the first customers.

06

Technical leadership

Senior technical ownership for startups that do not yet have a dedicated technical lead.

Let's talk

hello@illsv.com — a short description of the problem is enough to start.

07 — Tools

Technology

Supporting evidence, not identity.

Backend
Ruby · Rails · Go · Node.js
Data
PostgreSQL · Redis
Infrastructure
AWS · Docker · Kubernetes
Messaging
Kafka · RabbitMQ · NATS · Sidekiq
Frontend
TypeScript · React · Vue
Other
AI integrations · APIs · WebSockets · Web scraping

08 — About

Briefly

I'm a software engineer focused on backend systems, architecture and technical ownership.

Most of my work has involved taking complex product requirements, turning them into practical technical solutions, and carrying those solutions through implementation and production.

My background is strongly rooted in Ruby and Rails, but I care much more about solving the underlying engineering problem than about any particular technology.

Based in Kyiv, Ukraine.

Contact

Have a technical problem worth solving?