Ciarán Doyle
Senior Backend Engineer | Go, PostgreSQL, Kafka | Payments and High-Volume APIs
Summary
Backend engineer with 6 years building APIs and data pipelines, the last three in card payments. Designs services in Go and Python on PostgreSQL and Kafka, and cares about the unglamorous parts: idempotency, migrations that do not lock tables, and alerts that mean something. Currently owns the authorisation service at a Dublin payments company.
Experience
Senior Backend EngineerJan 2023 - Present
Lanyard Payments
- Own the card authorisation service in Go, which handles peaks of 2,000 requests per second at a p99 latency of 85 ms.
- Uptime of 99.95% over the last 12 months, up from 99.7%, after I added idempotency keys and retried writes through an outbox pattern.
- Split a 400,000-line monolith's ledger module into 3 services over 9 months with zero customer-facing downtime.
- Cut the monthly AWS bill for the team's services by €11,000 by right-sizing RDS instances and moving cold data to S3.
- Run the backend interview loop and have hired 5 engineers since 2024.
Backend EngineerAug 2020 - Dec 2022
Quayside Analytics
- Built REST and gRPC APIs in Python (FastAPI) serving dashboards to 180 retail customers.
- Rewrote the nightly import pipeline on Kafka; data freshness went from 24 hours to under 15 minutes.
- Wrote the zero-downtime migration guide the team still uses for PostgreSQL schema changes.
- Raised test coverage on the core API from 41% to 78%.
Skills
- Go
- Python (FastAPI)
- PostgreSQL
- Kafka
- REST and gRPC API Design
- AWS (ECS, RDS, S3, SQS)
- Docker and Terraform
- Distributed Systems
- Observability (Prometheus, Grafana)
- PCI DSS Awareness
Certifications
- AWS Certified Developer, Associate (2023)
Education
BSc (Hons) Computer Science, University College Dublin, 2020