Mercari's Platform Network team shares how they migrated a legacy image transformation pipeline to Cloudflare Images while keeping existing URLs intact. Key challenges included TLS/SSL issues with legacy S3 bucket naming conventions, egress cost estimation due to Cloudflare's different compression behavior (WebP files up to 50% larger), and zero-downtime rollout mechanics. They resolved S3 access via host-header-style routing with Terraform, validated image quality through pixel-level comparison and adjusted quality settings, estimated costs using 30-day APPROX_COUNT_DISTINCT queries on access logs, and rolled out traffic gradually using regex-based image ID matching (from 0.1% to 100%) with a three-phase cache rebuild strategy to avoid S3 rate limit overloads.
