We Let AI Agents Rewrite a 92M-Message-a-Day Service in Go (www.checklyhq.com)

Checkly announced the successful rewrite of its high-throughput Results Daemon, which processes around 92 million messages daily, transitioning from Node.js to Go with the assistance of AI agent Claude Code. This change is particularly significant for the AI/ML community, as it demonstrates the feasibility of employing AI for critical, production-level software development. The rewrite led to a remarkable 70% reduction in running pods and a lighter database load, showcasing Go's advantages, such as a stronger type system that enhances error detection and reduces potential regressions. The execution relied heavily on a meticulously designed test harness that ensured quality and correctness before any code was produced. Key developments included using Playwright for reliable testing, Docker Compose to manage environments, and Toxiproxy for simulating network conditions. The harness employed rigorous validation through golden files and comprehensive coverage of realistic input scenarios, further enabling the AI to produce a robust service architecture with 13,000 lines of code. Despite some initial challenges in production due to differences in local and production environments, the transition was methodically approached, utilizing feature flags for a staged migration to ensure stability and performance continuity.