Open to opportunities

Kevin O'Neill

@kevinoneill

Message

Senior backend engineer specializing in high-scale APIs, event-driven systems, and cloud-native platforms.

Ireland

Message

What I'm looking for

I seek senior/backend roles at companies valuing reliability, scalable APIs, and observability, where I can lead migrations, mentor engineers, and deliver high-impact systems.

I am a senior backend engineer with 7+ years building high-scale APIs, event-driven systems, and cloud-native platforms across EU and US product teams.

I have led monolith-to-microservice migrations, hardened reliability and observability, and shipped revenue-critical features for enterprise customers, improving availability and reducing operational costs.

My technical depth includes Go, C#/.NET, Node/TypeScript, Ruby on Rails, Postgres, and AWS/Azure/GCP, with strong skills in system design, data modeling, and performance tuning.

I prioritize secure, observable systems and mentor engineering teams to adopt best practices like CQRS, DDD, idempotent processing, and SLO-driven operations to deliver resilient, scalable products.

Experience

Work history, roles, and key accomplishments

Current

Staff-Track Backend Engineer

Current

Stedi

Nov 2024 - Present (1 year 3 months)

Building event-driven EDI translation services for healthcare on AWS serverless architecture, implementing CQRS and HIPAA-compliant security controls to ensure reliable, observable processing of X12 claims and remittances.

Go AWS Lambda API Gateway DynamoDB CQRS OpenAPI OAUTH2 Terraform

Senior Backend Engineer

Talon.One GmbH

Apr 2022 - Oct 2024 (2 years 6 months)

Built a real-time promotion evaluation engine in Go serving 10K+ RPS with <50ms p99, implemented DDD/CQRS, outbox/idempotency patterns to eliminate duplicate awards, and optimized Postgres/Redis to reduce DB CPU from 85% to 35%.

Go Kafka Postgres Redis CQRS DDD OpenAPI Prometheus Grafana

Senior Backend Engineer

Mews

Jan 2021 - Mar 2022 (1 year 2 months)

Led decomposition of a 500K+ LOC .NET monolith into 12 microservices, implemented Azure Service Bus event-driven workflows and OpenAPI contract testing, reducing synchronous cross-service calls 80% and enabling daily deployments.

C++.NET Azure Azure Service Bus OpenAPI Redis Kubernetes OAUTH2 Azure Key Vault

Backend Engineer

Fishbrain AB

Oct 2019 - Dec 2020 (1 year 2 months)

Developed GraphQL/REST APIs in Rails serving 5M+ users, migrated high-throughput ingestion to Go microservices reducing memory footprint 40%, and improved onboarding performance contributing to +12% user activation.

Ruby on Rails Go GraphQL Postgres Redis S3 Cloudfront Sidekiq Observability

Backend Engineer

Toggl OÜ

Jul 2018 - Sep 2019 (1 year 2 months)

Built Go microservices and gRPC internals for a 3M+ user platform, designed CDC pipelines to BigQuery for real-time analytics, and led GKE migration achieving zero-downtime deployments and faster incident recovery.

Go gRPC Postgres BigQuery Terraform GCP Docker GKE OpenTelemetry

Software Engineer Intern

Storyblok

Feb 2018 - Jun 2018 (4 months)

Developed TypeScript/Node.js microservices for headless CMS workflows, extended GraphQL/REST APIs with field-level auth and rate limiting, and improved CI test coverage with Jest to prevent regressions.